Backhoe Bucket

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The use of farming tractors, at home and commercially, has become more popular since it was first manufactured in 1868. First used as a type of hauling method for timber over roads, it then became more widely used when gasoline powered tractors were introduced. Since then there has been a wide range of available models from the simple lawn tractor for homeowners to larger scale farming tractors for large farmers.

When someone thinks of farming tractors the first name they think of is John Deere. While they started out with just one tractor they have quickly grown and now offer many options in tractors. Anywhere from riding mowers, push mowers, large and small tractors, sales, service, and repair. John Deere has made a household name for themselves with quality farming equipment for either residential or commercial use.

John Deere made their first product, a steel made plow to make it easier to dig through the hard soil in 1837. Adding retailing to their business in 1842 they continued building their empire over the years until it’s the company everyone knows now.

When selecting a tractor, it’s best to figure what you need it for. If you are looking for one that you can just mow your lawn at home you would do best with one of the John Deere riding mowers. Offered in a multitude of sizes and options you’re sure to find one that would best suite your needs. However, if you own a lot of land or own a farm, a larger tractor would be best for you. There’re tractors with backhoe attachments, tractors for crop building, leveling, etc. They also offer a wide range of used or pre-owned tractors.

If you are just looking for attachments for a tractor you already own, John Deere offers a large list of equipment available. Anywhere from rake attachments and backhoe attachments to skid steers. John Deer also carries a wide assortment of other farming equipment. They have loaders, skidders, walk behind mowers, balers, corn pickers, utility tractors, etc. No matter what your needs are you are sure to find it at John Deere.

Going back to about 25 years before today, Peugeot might be a brand that came with quite a high prestige to offer those who own one. This was possible thanks to the manufacturer’s 205 GTI which was considerably amazing back then. However, unfortunately, it seems that Peugeot has not been able to really amaze car enthusiasts any longer for decades. Yet, things are about to change for the manufacturer thanks to their new Peugeot RCZ which is a coupe one of its kind and has a lot to offer. After hearing all that, the next thing that may sound more interesting is often what the car can probably offer for real.

Well, to get things started, car enthusiasts worldwide may think of this Peugeot RCZ as a rival to the Audi TT. Every car enthusiast knows how Audi TT performs and what it can give to the drivers. With that being said, the car enthusiasts out there may have acquired the big picture of the coupe offered by Peugeot. However, it may turn out quite unfair just to look at the big picture instead of paying attention to every detail of the coupe. Therefore, it is wise to read on.

First of all, what Peugeot may offer to the car owners – and the one that may turn out the most innovative feature – is the so-called double bubble curving shape applied to the roof as well as the glass rear window of the RCZ coupe. This is one of the key factors that make Peugeot RCZ stand out from the rest of coupes from the other brands in existence. Peugeot has managed to lengthen this roof in such a way that it forms a fluid, single and streamlined envelope with the coupe’s rear window. As a result, optimized aerodynamics is something the driver of this coupe can expect. Also, the overall visual style of this particular coupe is an eye-catching one that will freeze the eyes of the surrounding crowd. It seems that people will not get tired of looking at this RCZ over and over again.

Then, the next item of innovation is the coupe’s aluminum roof arches which are meant to maximize the dynamism of the coupe. Viewed from the side, this particular coupe will proudly display the taut and firm contours supported by the coupe’s rear wings with generous curves, sides that are deeply sculpted and the coupe’s front wings which are very prominent.

Yet, another feature offered with the Peugeot RCZ is an enveloping bonnet. Thanks to such a bonnet, it has been possible for the manufacturer Peugeot to reduce the size that the front wings may have taken. Also, with its wide opening, accessing the engine as well as the front wheel arches becomes a lot easier.

In terms of performance, Peugeot offers 3 engine options for this outstanding coupe of theirs. First, there is the 1.6 THP 16V 200 bhp engine option. Then, there is the 1.6 THP 16V 156 bhp engine option. Those are for the petrol engines. Now, for the diesel engine, there is the 2.0 HDi FAP 16V 163 bhp engine option. And, when it comes to steering, this coupe is equipped with hydraulic power steering feature. Thanks to such a steering feature, this coupe can easily be driven through corners without the coupe losing its stability. And, the RCZ coupe responds very well to the steering in most occasions.

The braking system on the Peugeot RCZ is also a powerful one. With front ventilated discs measuring 302 millimeters in diameter and with a thickness of up to 26 millimeters, the braking system is a hard-wearing one. Meanwhile, for the rear braking system, this coupe comes offered for sale with brake discs measuring 290×12 millimeters. Yet, there are more to the braking system. The owners of this coupe may well expect the presence of EBA – which stands for Emergency Brake Assist – and EBD – which stands for Electronic Brake force Distribution. With these features, the brake pressure on each wheel is very likely to be pretty efficient.

To add to the driver’s driving pleasure, this particular coupe grasps the road perfectly. The coupe features an inverted type of pseudo McPherson assembly as its front suspension. The RCZ that comes with the 200 bhp engine option even features an anti-roll bar that is uncoupled. On the other hand, the rear suspension is a trailing-arm type featuring rigid arm joints. The base and the gravity center of the coupe have even been lowered as well for the sake of the driver’s pleasure.

However, what have been revealed so far with concerns to the coupe are all about the visual and technical aspects. What about the comfort that the Peugeot RCZ may offer? Well, in terms of comfort, Peugeot offers pretty smooth and high quality upholstery. Better yet, it is even possible for the RCZ owners to upgrade the upholstery to the superior Nappa leather. Yet, the seats inside the coupe are sports car typical. The position is low yet ergonomic providing a great level of comfort to the passengers inside.

Yet, when it comes to entertainment, this RCZ features a set of high technology equipments that may well include Peugeot’s new multimedia systems, JBL Hi-Fi systems, USB sockets and so on. And, unlike the other cars, there is an analog clock instead of a digital one in the center of the instrument panel. And, in order to reflect how a sports car may feel, the background of the instrument panel is made of genuinely pressed metal.

The steering wheel is also of fine quality. It is covered with fine leather. Better yet, it is even equipped with collar as well as thumb rests that are covered with chrome finishing. And, for easy readings for the driver, the dial backs come with carbon tone which is enhanced even further by making use of back-lit and laser cut readings.

Now, it seems that the least discussed item here is safety of the Peugeot RCZ coupe. Well, the coupe features driver and front passenger airbags along with 2 neck airbags built into its seats. Of course, the airbags are not the only items available when it comes to safety. Taking into consideration the new protocol of the Euro NCAP, Peugeot has equipped their RCZ coupe by means of a pyrotechnic pop-up bonnet. This bonnet is designed to minimize the impact pedestrians may experience should a collision takes place in the front side of the coupe.

Another safety feature is a spoiler. Peugeot RCZ comes with a self-adjustable spoiler that works accordingly to the speed of the coupe. The spoiler works in two positions. It will first open when the RCZ coupe reaches 53 mph. Then, the spoiler will extend even further if the coupe reaches a speed of up to 96 mph. By means of such a spoiler, this top-notch coupe will obtain an even higher aerodynamic efficiency.

After all being said, it may well be true that Peugeot may not have shown what it can do for decades. However, with the presence of Peugeot RCZ, those car enthusiasts or those who are perhaps intending to buy a sports car or a coupe may need to consider buying an RCZ. Yet, they need to keep in mind that there is a pretty good chance they can still find even more options available right from Peugeot.

One item that every farmer is familiar with is the backhoes. Many people rely on these get a tough job done, and there are many affordable versions available. They can be used in landscaping, farming, light construction, at nurseries, at golf courses, at cemeteries, and any other location that need a backhoe to get the job done.

What types of jobs can backhoes perform? The pieces of heavy machinery can dig holes, move heavy items, excavate, and much more! These tractors also go by many other names including JCB, rear actor, and back actor. Many companies make this heavy equipment tractor including John Deere, Caterpillar, Case, and New Holland. These really get a tough job done quickly. They typically have a digging bucket on the front of a two-part arm. This part of the vehicle is often referred to as the boom and dipper, or boom and dipper stick. These terms are interchangeable, and farmers and contraction workers referred to them either way. They are typically powered by hydraulics. Some people call the metal bar that is like a hinge attached the scoop the thumb.

This piece of heavy machinery was originally produced by the JCB Company. They are in English company, that started manufacturing this piece in 1953. The first American version was created in 1959, by the Hy-Dynamic company. A humorous part of this invention’s history is known as the backhoe fade. This term refers to damage done by backhoes. If a phone line gets dug up or cut, this is the term used to describe this occurrence. It is more of an inside joke between those who work with this equipment.

If you work in construction you are probably familiar with this helpful piece of equipment. If you have never worked with these before, and have no idea what it is, hopefully you have a better understanding of the product now. You have learned and nicknames, the uses, and who uses them. You even read a funny fact. Visit your local contraction site or farmer to try out one of these heavy pieces equipment for yourself. They are fun and easy to use once you learn how to run them.

Dave Gorski writes about backhoes at: http://www.backhoefacts.com

20 years ago, the United States, small Construction Machinery Just officially entered the horizon; 20 years after the United States, average Sell 3 sets of engineering Machinery Products, there is a platform for small construction machinery. At the global, annual skid steer loaders and backhoe loader sales have reached 10 million units, adjacent to China, India, every year two busy (ie backhoe loader) sold 2.5 million units … … Is one such industry in China has almost not been started. Currently, several existing small construction machinery manufacturing enterprises, each year the vast majority of products manufactured for export. But with the growing domestic infrastructure improvement and continuous improvement of living standards, and facilities maintenance and the rising demands of mechanized operations, small construction machinery market in China seems to have a real sniff of spring. China started a small construction machinery market has faint sound of horns could be heard. One machine can Alternative manpower, it is the user’s use of small construction machinery most intuitive impression. However, the mainstream view is that China’s current labor costs are very low, the use of small construction machinery products, the cost is much higher than labor costs. The short term, small construction machinery in China seems to be woeful. Even so, Vice President Liugong closed with Paula on small construction machinery market in China is expected to locate or not polite at 1 million units. He said, not replace human primary purpose of small construction machinery, in fact, the biggest advantage of small construction machinery is more than one machine can. Is equipped with different tools by small engineering machinery can be used in a variety of jobs. Western mainstream markets, small construction machinery users to buy products, matching the case with an average of 2 to 3; high cost of land in Japan, demand for small construction machinery is very large, but their small mining machine technology is more mature, skid steer loaders and backhoe loaders is the use of compression, the largest application is in northern Hokkaido, snow removal and other operations, so they are not much with the demand, generally 1 to 2; In Australia, as the market is more mature, this data is very high, by 4 ~ 5. In the actual construction, the small scale of operations involved in actually operating the form of a more trivial and complex, a job form obviously can not meet all the needs. Replacement of high cost multiple devices is unrealistic things, that the only solution is to replace the product is a. Therefore, for small manufacturers of construction machinery is different from other engineering machinery products, they must be committed to host R & D at the same time, put more energy into research and development is up with. As the pioneer of small-scale engineering machinery, Jiangsu Liugong has developed more than 100 species can be used in skid steer loaders and backhoe loader is a. Currently on the market mainstream skid steer loader, the user can without using any Tool , Is replaced within a minute of hand tools, to achieve an efficient operation possible. A real problem is that a small construction machinery is expensive, to some extent beyond the current capacity of the domestic customers. With the continuous development of Chinese enterprises, through a variety of ways to achieve and the host is a price reduction, the rapid rise of the market will be catalytic.

Between diminishing factory orders and increasing labor and energy costs, companies that use plate metal in their fabricating processes are finding their profit margins increasingly pinched.

Yet, manufacturers must still invest in new production equipment — whether to replace obsolete equipment or to take advantage of new business opportunities — in order to remain competitive.

Manufacturers must make careful assessments when evaluating the addition of new plate-rolling equipment. Debt capital is still available to purchase new machinery, but paying back the loan will not yield a satisfactory return on investment unless the equipment adds value to the production. Unfortunately, many buyers end up purchasing equipment that lacks the capability and flexibility to meet production volumes and tolerances, simply because they don’t understand all available options and considerations.

In an effort to help manufacturers optimize plate rolling operations, 5 key considerations are offered in order to choose a proper plate bending machine.

1. Factor in the properties of the material to be rolled

Even though drawings call for a plate to be rolled down to the same dimensions, a tougher material will require a much higher-rated rolling machine. In absence of such considerations, defects will result and the manufacturer will end up with excessive scrap.

Today’s steel is much stronger and requires more strength to bend. Thanks to detailed classifications by the American Society of Mechanical Engineers, countless varieties of steel abound: A36, A516 grade 70, Hardox 400/500 series and AR 200/300 series, for example. And these different steels require varying pressures to roll.

A metal’s temper and yield strength must be matched with the customer’s application to correctly determine the specifications of the plate roller. This is especially important since steel characteristics have changed drastically over the past couple of decades. What was once known as mild steel no longer exists.

2. Work with an equipment dealer that is willing to discuss your specific plate-rolling needs

Customers must know the correct questions to ask, in order to get the correct answers. Each manufacturer faces unique challenges, and through systematic querying an astute sales representative can determine exactly what equipment will work best for their process.

Manufacturers must also carefully consider whether they wish to roll conical or parabolic shapes to take advantage of a broader market. Hydraulically operated four-roll machines are ideal for this type of work by eliminating surface scarring, thereby decreasing the need for grinding the lamination (bullnosing) on the minor diameter edge of a cone.

Accurate conical rolling is further achieved through features such as torsion bar parallelism, as opposed to electronic systems or proportional value systems that merely maintain a theoretical balance. Finite parallelism allows the machine to be adjusted to its full conical tilt and back to parallel in only five seconds.

Customers need to discuss issues such as inside diameters, material type, tolerances and the desired shape of the finished product. As an example, some products, such as those found in the pressure vessel industry, demand a maximum of 1 percent out-of-round on their diameters or they are considered defective. By using an underpowered plate roller, too much of a barrel effect can render such a product useless and quickly erase any potential profit margin.

Matching plate-rolling equipment to the specific needs of a manufacturer requires attention to detail. It is imperative that the dealer you work with is willing to sit down with you and discuss the specific needs of your business. There are many issues that need to be addressed, many of which a purchasing manager may not initially foresee.

3. Stay within ideal operating parameters of the machine

It is recommended that manufactures identify what material and what thickness represent their highest volume of work. Then (a company) can deliver a machine that will camber to that specification, thus conserving valuable production hours and eliminating large amounts of scrap.

Quality rolling machines are usually cambered at 50 percent of the full-rated value of the machine. Hence, a 1-inch machine is cambered to roll 1/2-inch plate at a nearly perfect edge.
Disregarding this important fact can result in out-of-spec product that the customer will not accept. Problems most commonly arise when rollers attempt to push the upper limits of their plate roll. If 5/8-inch plate is rolled through a 1-inch-rated machine, a small degree of barrel effect will likely occur. This may or may not be an acceptable margin for error.
However, when plate thickness approaches the upper end of a machine’s rating, then severe defects can occur. Unless corrected with a shim, it will not be sellable. Conversely, when very thin material is rolled through a machine rated for very thick plate, the finished product may come out tighter in the center than at the ends. Again, time consuming shimming is necessitated to correct for this “hourglass” effect.

4. Carefully consider bending diameters

The tighter the diameter, the more bend pressure required. For instances where thick material must be rolled into tight inside diameters (ID), the diameter of the top roll and the layout of the machine can make the difference between a product whose cylindrical edges meet and one that won’t close.

As a rule of thumb, most machines can roll plate at 1 1/2 times the upper roll diameter. Hence, given a 10-inch-diameter top roll, inside diameters as tight as 15 inches can be obtained. However, new machines that incorporate planetary guides are able to keep approximately 50 percent more area of the plate under bend-pressure during the rolling operation, thereby achieving ratios of 1.1 times the upper roll diameter. This creates a 30 percent advantage on tight diameters.

All machines achieve precise measurements at 50 percent of the full-rated value. Therefore, given a 1.1 roll geometry, a 3/8-inch machine with a 10-inch top roller can consistently roll 3/16-inch plate to 11-inch ID without any barrel defect.

5. Incorporate both side and vertical supports to prevent unwanted bends

Adequate support requires both side and vertical roller-supports, as designed by the manufacturer of the plate-rolling machine. Once employed, plate rolling becomes a one-man job instead of two. This frees up valuable manpower that can be re-routed to other jobs.

When rolling a cylinder, once the inside diameter is more than 200 times greater than the thickness of the material, the weight of the material becomes sufficient to bend the cylinder as it exits the top roll and gets further away from the machine. Without proper support, unwanted radii result.
Purchasing a machine with both side and vertical roller supports easily solves this problem.Some manufacturers attempt to skimp on this ancillary equipment by resorting to “makeshift” support such as a forklift or overhead crane. However, this shortcut ties up the use of equipment that can best be utilized elsewhere. Because it cannot adequately support the material, unforeseen bends can still appear.

The world is facing a global crisis and during these tough times, all you need to do in order to survive is to be wise when it comes to making your decisions that involves a certain amount of money. You must know how to budget your money wisely especially when you have your own business. Through this you will still be able to survive in the industry and of course progress in whatever you are doing.

If you are into landscaping industry, you must be wise in utilizing what you have in order to survive with the tough times and of course succeed in your business. As a contractor, you will be offered with some projects and it can involve different tasks. When this happens, you must be prepared especially in making cost estimates for the whole project, how many workers you will need and of course what machines you will use.

Skid steer loaders are considered to be very versatile equipments used in the field of landscaping. There are heavy and compact sizes for this kind of equipment which makes it very useful in different kind of projects. During the tough times today, as a contractor, you must appreciate the benefits that this kind of equipment can do for you and your business in general. Once you know what you can do with it, you will realize how important it is to have in your business.

The Compact Track Loader is considered very versatile due to the various attachments that can be applied to it. You must have the knowledge of what you can purchase for the different tasks that you have in your landscaping project. There are many in the market that is why you will not encounter any problem as long as the attachment will match the type and size of your machine. With the different applications that you can use, you can experience a lot of advantages.

First of all, you are able to do a lot of specific jobs with the use of one machine which is your best Compact Track Loader. For instance, with the use of a bucket attachment, you can dig and excavate most especially if you are creating ponds to landscape a specific location. Aside from that, you can remove the attachment and use other applications like backhoe, fork, and a lot more. Specific tasks are efficiently done with the help of the different applications.

Another great advantage which makes it very helpful during the tough times today is that it helps in reducing your costs for your business. You do not have to buy a lot of equipments because with just one machine you are able to do the tasks that you needed. Instead of buying another whole landscaping machine, all you need to purchase are the different attachment needed.

The compact track loader is indeed very helpful especially for landscaping contractors who need to survive in the global crises today. Multiple tasks performed by just one equipment is what you will need in your business.

Skid steer loaders are very versatile equipments especially if you are going to use it for landscaping. They can be used with different kinds of attachments doing specific jobs. More can be read about this useful equipment at http://compact-track-loader.org/blog/.

Overview

The M60 is a belt-fed machine gun that fires the 7.62 mm NATO cartridge commonly used in larger rifles. It is generally used as crew-served weapon and operated by a team of two or three men. The team consists of the gunner, the assistant gunner (A-gunner in military slang), and the ammunition bearer. The gun’s weight and the amount of ammunition it consumes when fired make it difficult for a single soldier to carry and operate. The gunner carries the weapon and, depending on his strength and stamina, anywhere from 200 to 1000 rounds of ammunition. The assistant carries a spare barrel and extra ammunition, and reloads and spots targets for the gunner. The ammunition bearer carries additional ammunition and the tripod with associated traversing and elevation mechanism, if issued, and fetches more ammunition as needed during firing.

Firing an M60 machine gun from the standing position during the DEFENDER CHALLENGE ’88 competition

The basic ammunition load carried by the crew is 600 to 900 rounds and theoretically allows approximately two minutes of continuous firing at the maximum rate of fire. All crews carry more than the basic load, sometimes three or more times the basic amount.[citation needed]

The M60 can be accurately fired at short ranges from the shoulder due to its design. This was an initial requirement for the design and a hold-over in concept from the M1918 Browning Automatic Rifle. It may also be fired from the integral bipod, M122 tripod, and some other mounts.

M60 ammunition comes in a cloth bandolier containing a cardboard box of 100 pre-linked rounds. The M60 changed from M1 link to the different M13 link, a change from the older link system with which it was not compatible. The cloth bandoleer is reinforced to allow it to be hung from the current version of the feed tray. Historically, units in Vietnam used B3A cans from C-rations packs locked into the ammunition box attachment system to roll the ammunition belts over for a straighter and smoother feed to the loading port to enhance reliability of feed. The later models changed the ammunition box attachment point and made this adaptation unnecessary.

History

The M60 machine gun began development in the late 1940s as a program for a new, lighter 7.62 mm machine gun. The design included features that had been successful on earlier designs (most notably the German MG 42 and FG 42), as well as improvements of its own. It was intended to replace the M1918 Browning Automatic Rifle and M1919A6 Browning machine gun in the squad automatic weapon role. It was also to replace the M1919 family in the medium machine gun role. One of the weapons tested against it during its procurement process was the FN MAG.

The experimental T-44 machine gun developed from the German FG 42 and MG 42 machine guns.

The U.S. Army officially adopted the M60 in 1957. It later served in the Vietnam War as a squad automatic weapon with many U.S. units. Every soldier in the rifle squad would carry an additional 200 linked rounds of ammunition for the M60, a spare barrel, or both. The up-gunned M113 armored personnel carrier ACAV added two M60 gunners beside the main .50 gun, and the Patrol Boat, River had one in addition to two 50 cal mounts.

This section requires expansion with:

Fill in M60 history, including Vietnam War info.

M60 in Vietnam 1966.

In the 1980s, it was partially replaced by the M249 Squad Automatic Weapon within the Infantry squad. The M60 was retained in the vehicle mounted role and the general-purpose role due to its greater power and range compared to the 5.56 mm M249. In USMC service, concerns about the M60′s reliability, the system’s weight, and high round counts of many M60s in service prompted the adoption of the M60E3 to replace most original M60s in Infantry units.

A 19th Special Forces Group soldier mans an M60 machine gun on a HMMWV in Afghanistan, in March 2004. An AT4 anti-tank launcher can be seen in the foreground.

Starting with Ranger Battalions, the US Army began adopting and modifying M240 variants for replacing their remaining M60s in the early 1990s. By comparison, the M240 is several pounds heavier than the M60, and has a longer barrel and overall length, but is more reliable in use and testing.[citation needed] However, the M60 uses a much simpler gas system that is, when care is taken during reassembly, easier to clean. This advantage is obviated by the fact that, in practice, the gas tube is wired shut with lockwire to prevent the gun from disassembling itself due to vibration in hard use.

A sailor fires an M60E3 machine gun during a live-fire exercise at the Mobile Inshore Underwater Warfare Site (MIUW) at Guantanamo Bay, Cuba.

The M60 continues to be used by U.S. Navy SEALs and as a door gun on U.S. Army helicopters into the 21st century, and as the main 7.62 mm machine gun by some U.S. special operations forces into the late 1990s. As of 2005, it is used by the Coast Guard, Navy, and a number of reserve forces, though it is being phased out in favor of the M240 7.62 mm medium machine gun. The use as an Army helicopter door gun will soon be tapering off, as an improved M240 version has been adopted for this role.

Design

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The M60 is a gas-operated, air-cooled, belt-fed, automatic machine gun that fires from the open-bolt position and is chambered for the 7.62 mm NATO cartridge. Ammunition is usually fed into the weapon from a 100-round bandolier containing a disintegrating, metallic split-link belt.

An Airwoman of the UK’s Royal Air Force handles an M60 during a demonstration for Combined Joint Task Force Exercise (CJTFEX) in 2004

The design drew on many common concepts in firearms manufacture of the period, such as stamped sheet metal construction, belt feed (a modified mechanism for belt feed from the MG42 with a single pawl), quick barrel replacement, a pistol grip and stock, and a semi-bull pup design similar to the FG42 (much of the action occupies the weapon’s stock). The M60′s operating system of an operating rod turning a rotating bolt was inspired by the FG42, which was based on the much earlier Lewis Gun. The M60′s gas operation is unique, and drew on technical advances of the period, particularly the White “gas expansion and cutoff” principle also exploited by the M14 rifle. The M60′s gas system was simpler than other gas systems and easier to clean.

The straight-line layout allowed the operating rod and buffer to run directly back into the buttstock and reduce the overall length of the weapon.

As with all such weapons, it can be fired from the shoulder, hip, or underarm position. However, to achieve the maximum effective range, it is recommended that a bipod-steadied position or a tripod-mounted position be used and fired in bursts of 35 rounds. The weapon is heavy and difficult to aim when firing without support, though the weight helps reduce the felt recoil. The large grip also allowed the weapon to be conveniently carried at the hip. The gun can be stripped using a live round of ammunition as a tool. However, this is highly discouraged, as doing so can damage that round and increase the chance of a misfire.

The M60 is often used with its own integrated bipod or with the M122 tripod. The M60 is considered effective up to 1,100 meters when firing at an area target and mounted on a tripod; up to 800 meters when firing at an area target using the integral bipod; up to 600 meters when firing at a point target; and up to 200 meters when firing at a moving point target. United States Marine Corps doctrine holds that the M60 and other weapons in its class are capable of suppressive fire on area targets out to 1,500 meters if the gunner is sufficiently skilled.

Originally an experimental M91 tripod was developed for the M60, but an updated M2 tripod design was selected over it which became the M122. The M122 would be itself replaced in the 2000s by a new mount, in time for the M60 to also be used with it.

Ammunition

M60 machine gun fired during a small arms familiarization exercise aboard USS Blue Ridge (LCC-19); November 2004

810th Military Police Company, mans a 7.62 mm M60 machine gun atop an M998 High-Mobility Multipurpose Wheeled Vehicle (HMMWV) during Operation Desert Shield.

The M60 family of weapons are capable of firing standard NATO rounds of the appropriate caliber. Most common in U.S. use are M61 Armor piercing, M62 Tracer, and M80 Ball. For training purposes, M63 Dummy and M82 Blanks are used. The new tungsten cored M993 Armor-piercing rounds may also be fired in the M60 as well, though they did not enter the inventory until after the M60 was withdrawn from service in active-duty units.

When firing blanks, the M13 or M13A1 blank-firing adaptor (BFA) is necessary in order to produce enough gas pressure to cycle the weapon with blanks. All ammunition must be fixed in a NATO standard M13 disintegrating metallic split-link belt to feed into the weapon.

The standard combat ammunition mix for the M60 consists of four ball (M80) cartridges and one tracer (M62) in belts of 100 rounds. The four to one ratio theoretically allows the gunner to accurately “walk” the fire into the enemy. Tracer bullets do not fly quite the same trajectory as ball and weapon’s sights must be used for accurate firearticularly at ranges in excess of 800 meters, where 7.62x51mm NATO tracer bullets usually burn out and are no longer visible. This is a problem for all weapons in this caliber using this tracer round.

Design flaws

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An M60 machine gun aboard a Navy patrol craft. The USS Constellation (CV-64) is visible in the background.

When tested in the field, the M60 was fairly effective, but in the jungles of Southeast Asia in which it was soon used, the initial versions displayed several potential problems when used on the ground. A common complaint was the weapon’s weight, though M60 was among the lightest 7.62 mm machine guns of the era.

For units in Vietnam, the single most common complaint was that the M60 was comparatively unreliable and prone to jamming and other malfunctions, especially when it was dirty. Fine sand and dust in the mechanism could bring the M60 to a halt. This was a major factor in the Israeli Defense Force declining to adopt the M60. The weapon was more difficult to clean and maintain than the M1918A2 Browning Automatic Rifle (BAR) it replaced in the squad. In normal conditions it would often fire thousands of rounds without a serious jam while field conditions tended to reduce reliability without proper maintenance.

The safety was awkward to operate and worked the “wrong way” for soldiers who were trained with the M16 rifle and M1911A1 pistolhat is, it required an upward movement of the thumb on the safety catch to make the gun ready to fire, rather than a downward movement as with the other weapons. Additionally, it is possible to install some of the fire control mechanism incorrectly, causing a “runaway gun”eaning that it would keep firing until empty even if the operator took his finger off the trigger. The gas system of the original model could be assembled incorrectly causing failure to function and could unscrew and come apart if not safety wired in place.

A Gunner Mate 3rd Class in the process of preventative maintenance and cleaning on an M60 machine on the USS Constellation (CV-64); December 2002

The M60 sometimes (depending on the version) tore rims off of fired cartridge cases during the extraction cycle, resulting in failure to remove the empty case, causing a jam that could take time to clear. The barrel latch mechanism (a swinging lever) could catch on the gunner’s equipment and accidentally unlatch, causing the barrel to fall out of the gun. The lever was replaced with a pushbutton mechanism that was less likely to be accidentally released, but many of the swinging-lever latches are still on guns in inventory, forty years after this problem was discovered.

The grip/trigger housing assembly is held in place with a rather fragile leaf spring clip instead of the captive pins used in other designs. The spring clip has been known to be prone to breakage since the first trials at Aberdeen Proving Ground. Duct tape and cable ties have been seen on M60s in the field, placed there by their crews in case the spring clip breaks. The sear in the trigger mechanism gained a reputation for wearing down and a malfunction could cause the gun to “run away”. A second sear notch was eventually added to the operating rod to reduce the chance of this happening.

Several critical parts of early production M60s, such as the receiver cover and feed tray, were made from very thin sheet metal stampings and prone to bending or breaking; sturdier parts were eventually available in the early 1970s. Early M60s also had driving spring guides and operating rods that were too thin and gas pistons that were too narrow behind the piston head (part of an attempt to save weight), leading to problems with breakage. Metallurgical problems also played a part, (blamed by some on low-bid contractors), but after 1970 a slightly heavier part was designed and slowly put into the supply chain. High round count weapons were also susceptible to stretching of the receiver and other parts.

An M60 machine gun team changes barrels before engaging their last target during the DEFENDER CHALLENGE ’88 competition.

Another criticism with some versions of the M60 is that the barrel was heavy. The bipod was a permanent fixture to the barrel as well as the gas chamber of the gas system; the latter was a result of using a piston design with a fixed regulator design. The advantage of the fixed regulator was no adjustment was required, though it risked the ability to compensate for fouling of the gas system, leading to insufficient power to operate the action, including lifting the ammunition belt. The non-adjustable front sight is fixed to the barrel and adjustments for “zeroing” the sights could only be made at the rear sight requiring readjustment when the barrel is changedot ideal for combat situations.

There was no handle to hold the barrel by for changes. A large asbestos glove was part of the standard issue to allow the crew to handle hot barrels during barrel change. Loss of the glove was always a problem.

U.S. Marines especially disliked the M60, and many Marine units held onto their BARs until 196768 officially, and longer unofficially. The M60E3 variant designed in the mid-1980s for the U.S. Marine Corps, reduced the design’s weight to 18.9 lb (8.61 kg) unloaded and slightly improved reliability. Users complained about the quickly-overheating barrel, a common problem with the original M60. This problem was aggravated in the M60E3, which uses a lighter barrel, which required changing every 100 rounds instead of every 200. The M60E3′s barrel used a wire and plastic handle near the breech end and could be changed safely without the use of heat-resistant mittens.

The U.S. Navy special operations forces continued to use and upgrade the M60E3 for years because of its portability and low weight for its caliber requiring many modifications, including a change in feed system and barrel configuration. Additional required changes were the addition of rails for optical sights and other modern accessories.

The reliability problem with the M60 machine gun was even more evident when the gun was compared to the successful and reliable PK machine gun used by Warsaw Pact forces and Soviet client states.

Variants

A member of the 101st Airborne Division, armed with an M60 machine gun, participates in a field exercise in 1972.

The nomenclature M60 describes either the first adopted version or, generically, the family of weapons derived from it.

Major variations include the M60E1 (an improved version that did not enter production), the M60E2 (a version designed to be used from fixed mounts as a co-axial for armored vehicles or in helicopter armament systems), the M60E3 (a lightweight version) and the M60E4 (another improved version, designated Mk 43 Mod 0 by the U.S. Navy).

The M60C was adopted for use on fixed mounts on aircraft. It was characterized by the use of an electric solenoid to operate the trigger and a hydraulic system to charge the weapon. The M60D differed from the base model by employing spade grips, a different sighting system, and lacking a forearm. It was typically employed as a door gun on helicopters or as a pintle mounted weapon as on the Type 88 K1 tank.

There are many smaller variants among each type, between makers of the firearm, and over time.

Variant summary

T161: The M60′s developmental designation before it was type-classified in the 1950s.

M60: The basic model, type-classified in 1957.

M60E1: An improved version that did not enter production. The primary difference was the handle fixed to the barrel and the removal of the gas cylinder and bipod from the barrel assembly.

M60E2: Used in vehicles as a coaxial machine gun; electrically fired.

M60B: Used in helicopters in the 1960s and 1970s; unmounted.

M60C: Used in fixed mounts in aircraft in the 1960s and 1970s; electrically fired and hydraulically charged.

M60D: Replaced the M60B; a pintle-mounted version used especially in armament subsystem for helicopters, but also some other roles.

M60E3: An updated, lightweight version adopted in the 1980s.

M60E4 (Mk 43 Mod 0/1): An improved model of the 1990s that looks similar to the E3, but has many improvements. It has subvariants of its own, and is also used by the U.S. Navy (as the Mk 43 Mod 0/1). The Mk 43 Mod 1 is a specialized version with additions such as extra rails for mounting accessories.

M60

M60 on the deck of USS Theodore Roosevelt (CVN-71) in 2006.

The initial version was officially adopted by the U.S. Army in the late 1950s, though at this time it was only intended for the infantry. It was known as the T161 before it was adopted (specifically the T161E3), and was chosen over the competing T52 during testing in the 1950s. They both used a similar feed and were both gas-operated, but the T161 was easier to produce and its different internals performed better. The model that won the competition was the T161E3.

The model was type-classified in 1957, and entered production. It saw its first heavy use in the 1960s. The basic design has undergone some smaller changes, and has been produced by different manufacturers.

M60E1

The M60E1 was the first major variant of the original M60. It did not go into full-scale production, though many of its features were included into the later E3 and E4 variants. Some of its features were also incorporated into the existing M60 production. This mainly changed how the gas cylinder, the barrel, and the bipod were connected; in the first iteration. The M60 and the M60E1 are two different versions. Opinions are varied on whether the M60E1 was officially adopted or not.

A camouflaged infantryman armed with an M60 machine gun.

One of the more noticeable changes on the M60E1 is that the bipod attachment point was moved to the gas tube rather than the barrel (like on the later M60E3). It did not, however, have a forward pistol grip, as was added on the E3.

M60E2

M60E2, intended for co-axial use. Note gas tube extension and no grip.

The M60E2 is used on armored fighting vehicles, such as the M48A5, later M60 Patton versions and the K1 Type 88. It lacks many of the external components of the standard M60, including stock and grips. The M60E2 was electrically fired, but had a manual trigger as a backup, as well as a metal loop at the back for charging. The gas tube below the barrel was extended to the full length of the weapon to vent the gas outside the vehicle. This version achieved a mean time between failures of 1,669 during testing in the 1970s, more frequent than the FN MAG, which was adopted in 1977 as a co-axial vehicle gun and designated the M240.

The M60E2 is used on the South Korea’s K1 Type 88 tank as a co-axial weapon, along with an M60D on a pintle mount.

M60B

The M60B was a short-lived version designed to be fired from helicopters, with limited deployment made in the 1960s and 1970s. It was not mounted, just held, and was soon replaced by the pintle-mounted M60D. The ‘B’ model differed most noticeably in that it had no bipod and featured a different rear stock than the regular model. It still had a pistol grip (as opposed to spade grips). The M60B’s advantage over pintle-mounted variants was that it had a wider and much less restricted field of fire.

M60C

The M60C machine gun.

The M60C is a variant of the standard M60 for aircraft-mounting, such as in helicopter armament subsystems. It lacks things like the bipod, pistol grip, and iron sights. The main difference between the standard M60 and the “C” variant is the electronic control system and the hydraulic swivel system used. It could be fired from the cockpit by the pilot or co-pilot. It is an electronically-controlled, hydraulic-powered, air-cooled, gas-operated, belt-fed weapon system. It used the M2, M6, and M16 armament subsystems and was mounted on the OH-13 Sioux, the OH-23 Raven, the UH-1B Huey, and comprised the standard fixed armament of the OV-10 Bronco. M60C production was on the order of several hundred. It was also used in the XM19 gun pod.

See also: US Helicopter Armament Subsystems

M60D

The M60D on the M23 Armament Subsystem.

The M60D is a mounted version of the standard M60. It can be mounted on boats, vehicles and as a pintle-mounted door gun in helicopters. When used in aircraft, it differs from the M60C in that it is not controlled by the pilotather, it is mounted in a door and operated by a member of the crew. Like the rest of the M60 family, it is an air-cooled, gas-operated, belt-fed weapon. Unlike other models, however, the M60D normally has spade grips and an aircraft ring-type sight or similar, as well as an improved ammunition feed system. A canvas bag is also affixed to the gun to capture ejected casings and links, preventing them from being sucked into the rotor blades or into an engine intake. The M60D was equipped on the UH-1B Huey (using the M23, XM29, M59, and the Sagami mounts), the CH-47 Chinook (using the M24 and M41 mounts) in both door and ramp locations, the ACH-47A “Guns-A-Go-Go” variant of the Chinook (using the XM32 and XM33 mounts), and on the UH-60 Black Hawk (using the M144 mount). The M60D is also used by the British on Royal Air Force Chinooks. In US service, the M60D are being replaced, primarily by the M240H.

See also: US Helicopter Armament Subsystems

M60E3

Navy SEAL team member fires an M60E3 from the shoulder during a field training exercise in 1987.

The M60E3 was fielded circa 1986 in an attempt to remedy problems with earlier versions of the M60 for infantry use. It is a lightweight, “improved” version intended to reduce the load carried by the gunner. Unlike its predecessors, the M60E3 has several updated modern features. It has a bipod (attached to the receiver) for improved stability, ambidextrous safety, universal sling attachments, a carrying handle on the barrel, and a simplified gas system. However, these features also caused almost as many problems for the weapon as they fixed. There were different types of barrels used, but the lightweight barrel was not as safe for sustained fire at 200 rounds per minute as heavier types. However, some personnel claim to have witnessed successful prolonged firing of the weapon. The stellite superalloy barrel liner makes it possible, but the excessive heat generated by this process can quickly make the gun unusable. There were two main barrels, a lightweight barrel and another heavier typehe former for when lighter weight was desired, and the latter for situations where more sustained fire was required.

M60E3.

The reduced-weight components also reduced the durability of the weapon, making it more prone to rapid wear and parts breakage than the original. Most infantry units in the U.S. Army and Marine Corps have now switched over to the M240 as their general-purpose machine gun, which is more reliable (particularly when dirty) and seems to be well-liked by the troops for its ruggedness, despite the fact that it weighs 27.6lb (12.5kg) compared to the standard M60 at 23.15lb (10.5kg).

The U.S. Air Force Security Forces received the M60E3 from 1988 to 1989. All USAF M60E3s were withdrawn from general issue by 1990, because it did not meet the vehicle mount requirements of the Cadillac Gage Ranger and due to overheating problems. The M60E3 did remain in the Air Force as an emergency issue weapon only. Still in service on Ohio Class ballistic missile submarines as a more reliable weapon has not even been considered for reissue.

M60E4 and Mk 43 Mod 0/1

This firearm is the latest generation of the M60 family and incorporates a number of improvements over other versions. Externally, it looks somewhat like the M60E3, but it has other internal changes and improvements. It features a different forward grip and is also a more reliable weapon than the other M60s. The M60E4/Mk 43 has higher pull for the belt, and is available in a variety of configurations. It is also possible to convert some older models to this standard. The M60E4 and Mk 43 were primarily developed in the 1990s. First the E4, and soon after the Mk 43hese early Mk 43s had some distinct differences from the E4 (such as a duckbill flash suppressor), though by the 2000s these distinctions seemed to have ended.

A mounted Mk 43 Mod 0 (M60E4) (later model) is crewed by a Seabee of NMCB-15 (Naval Mobile Construction Battalion), on a convoy in Iraq in May 2003.

This version also has another designation under the Navy, Mk 43 Mod 0. The Mk 43 Mod 0 was developed for the U.S. Navy SEALs to replace their existing stock of M60E3 machine guns fitted with shorter “assault barrels”. These weapons are identical to standard M60E4s, with the exception of the barrel length, and can be used either as suppressive fire or direct fire weapons, at least in terms of theory and training. The Mk 43 Mod 1 adds significantly more rail attachment points to the weapon’s receiver cover and handguard.

The M60E4 and Mk 43 versions are roughly similar, although they are only part of the same family. While it might be fair to say that the Mk 43s are a type of M60E4, there are technical differences between any given M60E4 model. Early Mk 43s have certain differences over M60E4 from the same period, the most obvious being the duck-bill flash hider and different handguard. Current Mk 43s do not have these differences however, and the U.S. Ordnance website states in their FAQ, as of 2005, that the “M60E4 and the Mk43 are the same weapon system”.

The M60E4 was pitted against the (then called) M240E4 in Army trials during the 1990s for new medium machine gun for the infantry, in a competition to replace the decades-old M60s. The M240E4 won, and was then classified as the M240B. This led to 1,000 existing M240s being sent to Fabrique Nationale for an overhaul and a special kit that modified them for use on ground (such as a stock, a rail, etc.). Afterwards, procurement contracts were let in the late 1990s for all-new M240B models. However, a new feature was added: a hydraulic buffer system to reduce the felt recoilimilar to that of the M60as incorporated. While the M240B had been more reliable in the tests, it was a few pounds heavier than the M60E4.

The M60E4 is not just another version, but a whole update to the series, that is also available in many of the previous configurations, such as a co-axial weapon. Kits are also offered to convert older models to the E4 standard.

M60E4 (Light machine gun):

Short barrel: weight: 22.5 lb (10.2 kg); length: 37.7 in (95.8 cm)

Long barrel: weight: 23.1 lb (10.5 kg); length: 42.4 in (108 cm)

Assault barrel: weight: 21.3 lb (9.66 kg); length: 37.0 in (94.0 cm)

Width: 4.8 in (12.2 cm)

M60E4 (mounted):

Length: 43.5 in (110 cm)

Width: 5.9 in (15.0 cm)

Weight: 22.7 lb (10.3 kg)

M60E4 (co-axial):

Length: 42.3 in (107 cm)

Width: 4.8 in (12.2 cm)

Weight: 21.2 lb (9.62 kg)

Civilian versions

A number of semi-automatic versions for the civilian market have been produced in the United States. The internals must be extensively modified to make it essentially impossible to convert them to fully-automatic weapons. If the design is approved by the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives (BATFE), they are treated as belt-fed semi-automatic rifles; however, individual state and local regulations still apply.

The U.S. Ordnance company is the current maker authorized by Saco to produce mil-spec M60s and M60 parts. However, U.S. Ordnance put its civilian semi-auto sales on hold until 2006 because its production capacity is required for government orders. The company had charged $8000 for a new semi-automatic M60.

The Desert Ordnance company is a current maker of M60s and M60 parts. The company charges between $13000-$14000 for a new semi-automatic M60, depending on the model.

Various makes of older fully-automatic versions are on the market as well, but there are many legal requirements to be met before purchasing them, and they cost upwards of U.S. $20,00030,000. This is largely due to the restriction on the production of fully-automatic firearms in the U.S. for the general civilian market since 1986. The combination of banning production and importation has led many to think it is illegal to own a machine gun, when, in fact, it is legal to own and use a fully-automatic M60 machine gun in the United States (unless prohibited by other state or local laws).

Users

Republic of Korea soldiers with an M60 conduct combined amphibious landing during Foal Eagle 07.

Moro Islamic Liberation Front militant laying prone with an M60.

Portuguese Army V-150 Commando armed with an M60.

 Australia

 Colombia

 Czech Republic: The M60E4 is used in small numbers by specialized units of the Czech Army.

 Egypt

 Greece

 Jordan

 Panama

 Peru

 Philippines

 Portugal: Portuguese Army uses M60E and D mounted on V-150 Commando.[citation needed]

 Republic of Korea

 Taiwan

 Thailand

 Tunisia

 United States: Used by the US Army and the US Navy SEALs.

See also

Military of the United States portal

Airman with M60, assigned to the 52nd Security Forces Squadron (SFS), at Spangdahlem Air Base (AB), Germany.

PK machine gun, M60′s Warsaw Pact counterpart.

List of individual weapons of the U.S. Armed Forces

List of crew-served weapons of the U.S. Armed Forces

References

^ a b The M60. Federation of American Scientists.

^ Weapons: An International Encyclopedia From 5000 B.C. To 2000 A.D. Diagram Visual, p. 217. ISBN 0-312-03950-6.

^ “Gun Control : Machine Guns”. Guncite.com. 2005-02-19. http://www.guncite.com/gun_control_gcfullau.html. Retrieved 2009-07-06. 

^ a b c d e f g h i j k {{cite web |url=http://www.worldpolicy.org/projects/arms/reports/smallarms.htm |title=Profiling the Small Arms Industry

^ http://www.army.cz/assets/files/9334/zbrane_definit.pdf

^ http://www.timawa.net/pmc.htm

^ Miller, David (2001). The Illustrated Directory of 20th Century Guns. Salamander Books Ltd. ISBN 1-84065-245-4.

^ M60E3 & Mk43 Mod 0

Global Security: the M60E3

Modern Firearms & Ammunition: the M60

Department of the Army Field Manual No. 3-22.68

U.S. Army TACOM Rock Island

MCWP 3-15.1 United States Marine Corps: “Machine Guns and Machine Gun Gunnery”

Navy SEALs

M60E4

External links

Wikimedia Commons has media related to:

M60 (machine gun) (category)

US Ordnance Website (Current maker of M60s)

Military Factory Small Arms

Belt-Fed FG42: Predecessor to the M60

US Army manual: Operator’s Manual For M60, M122, M60D

Video links

Nazarian`s Gun`s Recognition Guide (FILM) M60 Presentation (.MPEG)

v  d  e

General Purpose Machine Guns (GPMG)

AA-52  AEK-999  FN MAG  M60  Heckler & Koch HK21  Kucher Model K1  MG 34  MG 42  MG 3  Type 67  Type 80  SIG MG 50  MG 51  SIG MG 710-3  PK  Pecheneg  Sumitomo NTK-62  Uk vz. 59  UKM-2000  Vektor SS-77  Zastava M84

v  d  e

Current U.S. infantry weapons and cartridges

Handguns

M9  M11  MEU(SOC)  Mk 23  Mk 24

Rifles

Assault and Battle

M16  Mk 14  Mk 16

Carbine

HK416  M4  Mk 18

Designated Marksman

DMR  M14  M39  Mk 12  SAM-R  SDM-R  SEAL Recon Rifle

Sniper

M24  M40  M107  M110  Mk 11  Mk 15

Shotguns

M26  M590  M870  M1014

Submachine guns

MP5N  P90

Machine guns

M2HB  M240B  M249 and Mk 46  Mk 43

Grenade launchers

M203  M32  M320  M79  Mk 19  Mk 47

Mortars

M120  M224  M252

Rockets

M3  M72 series  M136  M141  M202A1  Mk 153

Missiles

FGM-172  FGM-148  FIM-92

Cartridges

12-gauge  5.7x28mm  9x19mm NATO  .45 ACP  5.56x45mm NATO  7.62x51mm NATO  12.7x99mm NATO

v  d  e

Current equipment of the United States Air Force

Aircraft

Attack

A/OA-10A/C Thunderbolt II  AC-130H/U Spectre/Spooky II

Bomber

B-1B Lancer  B-2A Spirit  B-52H Stratofortress

Electronic Warfare

E-3B/C Sentry  E-4B  E-8C Joint STARS  E-9A  EC-130J Commando Solo

Fighter

F-15C/D Eagle  F-15E Strike Eagle  F-16C/D Fighting Falcon  F-22A Raptor

Reconnaissance

OC-135B Open Skies  RC-26B  RC-135S/U/V/W  RQ-4A Global Hawk  RQ-11B Raven  RQ-170 Sentinel  U-2R/S Dragon Lady  WC-130J Super Hercules  WC-135C/W Constant Phoenix  Scan Eagle  Wasp III

Search and Rescue

HH-60G/MH-60G Pave Hawk   HC-130P/N

Tanker

KC-10A Extender  KC-135E/R/T Stratotanker

Trainer

T-1A Jayhawk  T-6A Texan II  (A)T-38A/B/C Talon  T-43A  TG-10B/C/D  TG-15A/B

Transport

C-5A/B/C/M Galaxy  VC-9C  C-12C/D/F Huron  C-17A Globemaster III  C-20A/B/C Gulfstream III  C-20G/H Gulfstream IV  C-21A Learjet  CV-22 Osprey  VC-25A  C-32A/B  C-37A Gulfstream V  C-37B Gulfstream V  C-38 Courier  C-40B Clipper  C-41A Aviocar  C-130E/H/J Hercules

Utility/Multi-Mission

LC-130H  MC-130 Combat Talon I,II/Combat Spear/Combat Shadow  MQ-1B Predator  MQ-9 Reaper  U-28A  UH-1H/N/V Huey  UV-18A/B Twin Otter  YAL-1

Space Systems

Launch Vehicle

Atlas V  Delta II  Delta IV

Satellite

Defense Meteorological Satellite Program (DMSP)  Defense Satellite Communications System (DSCS)  Defense Support Program (DSP)  Global Positioning System (GPS)  Milstar Satellite Communications System  Mobile User Objective System (MUOS)  Space-Based Infrared System (SBIRS)  Wideband Global SATCOM

C2

AN/USQ-163 Falconer

Munitions

Bomb

CBU-87 Combined Effects Munition  CBU-89 Gator  CBU-97 Sensor Fuzed Weapon  GBU-10 Paveway II  GBU-12 Paveway II  GBU-15  GBU-24 Paveway III  GBU-27 Paveway III  GBU-28  GBU-31 JDAM  GBU-32 JDAM  GBU-38 JDAM  GBU-39 Small Diameter Bomb  GBU-54 Laser JDAM  Mk-82  Mk-84  M129

Missile

AGM-65A/B/D/E/G/G2/H/K Maverick  AGM-86B/C/D Air-Launched Cruise Missile (ALCM)  AGM-88A/B/C High-speed Anti-radiation Missile (HARM)  AGM-130 Powered Standoff Weapon  AGM-154A Joint Standoff Weapon (JSOW)  AGM-158 Joint Air-to-Surface Stand-off Missile (JASSM)  AIM-7M Sparrow  AIM-9M/X Sidewinder  AIM-120B/C Advanced Medium-Range Air-to-Air Missile (AMRAAM)  LGM-30G Minuteman III

Target

BQM-34 Firebee  BQM-167 Subscale Aerial Target  MQM-107 Streaker  QF-4 Aerial Target

Small Arms

M4 Carbine  M9 Semiautomatic Pistol  M11 Semiautomatic Pistol  M1911A1 Semiautomatic Pistol  M14 Stand-off Munitions Disruptor (SMUD)  M16A2 Rifle  M18A1 Claymore Mine  M24 Sniper Weapon System  M67 Fragmentation Grenade  M79 Grenade Launcher  M107/M82A1 Long Range Sniper Rifle  M2 .50-Caliber Machine Gun  M240B Medium Machine Gun  M249 light machine gun  M60 Medium Machine Gun  MCS 870 Modular Combat Shotgun  MK-19 40 mm Machine Gun  MP5K Submachine Gun  UZI Submachine Gun  M72 Light Anti-tank Weapon (LAW)  GAU-5A/GUU-5P Carbine  M136 AT4 Light Anti-tank Weapon  Mk 14 Mod 0 Enhanced Battle Rifle

Categories: General purpose machine guns | Cold War infantry weapons | 7.62 mm machine guns | Machine guns of the United States | Aircraft guns | Modern infantry weapons of Australia | Vietnam War infantry weapons of Australia | Historical United States Coast Guard weaponsHidden categories: All articles with unsourced statements | Articles with unsourced statements from July 2009 | Articles to be expanded from July 2009 | All articles to be expanded | Wikipedia expand-section box with explanation text | NPOV disputes from July 2009 | All NPOV disputes | Articles needing additional references from July 2009 | All articles needing additional references | Articles with unsourced statements from February 2010 | Articles lacking in-text citations from July 2009 | All articles lacking in-text citations

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1 Introduction
<BR> Analog cable TV digital set-top boxes are used to receive digital TV programs, to provide broadcast and interactive multimedia applications terminals. Recently, with the digital media business and the rapid development of Internet networks, the new digital set-top box can use our enormous resources in the cable television network, complete video on demand, digital television receivers, IP phone and access Internet and other network integrated business functions. The digital set-top box to decrypt a single charge has been previously installed into Annals compression, modulation and demodulation, decryption, and interactive control as one charge of digital transmission and terminal equipment.
<BR> New digital set-top box to the number of family businesses to integrate with a device to meet the future needs of home users. But since their complexity, there are many new technical challenges, such as: how to effectively coordinate and manage digital TV, IP phone, Internet connection and other integrated services; present, many set-top boxes are one-way or return through telephone lines, and how video on demand and other new services and so on. Therefore, we need to select the higher frequency, data throughput, with broadband interactive features and cost-effective processing chip and the low quality software platform to complete the Management Module.
<BR> 2, program design and chip select
<BR> First conducted a needs analysis of digital set-top boxes, digital set-top box through to home users, while providing Internet access, digital TV and IP telephone services, and can carry a wealth of value-added services. Interface mode based on business needs and the new digital set-top hardware architecture modular design, including the external Ethernet interface module, the internal Ethernet interface module, analog subscriber line interface module, audio and video decoding module and the central management module. External Ethernet interface modules and Ethernet interface between the external network, internal Ethernet module provides indoor computer’s Ethernet interface, analog subscriber line interface provides two analog telephone interface; audio and video decoding module provides decoding output of the way digital TV and related interactive features; management module is responsible for the business flow and interface protocol conversion. First, the external Ethernet interface to receive external routers or switches forward the data frame, the solution will be packaged, transferred to the network processor diversion by three kinds of operations; audio and video decoder to receive the main control chip processing module after the TS data stream diversion , for MPEG-2 decoding, the output to PAL / NTSC encoder, encode analog television signals; internal Ethernet interface to receive IP data packets, encapsulated into MAC data frame sent to the computer terminal; IP call processing module through the CODEC codec digital signal and analog chips to complete the conversion and rushed to analog voice phone.
<BR> In the design of this article, the central management module to complete the IP phones (voice), the family line (Integrated Data Service) and digital television (video business) 3 business gateway function. After analysis and comparison of selected Samsung products S3C4510B ARM7 family as its main processing chip. S3C4510B for embedded applications is a 16/32 bit embedded processor, the micro-controller for Ethernet hubs and routers, communication systems are designed with low cost and high performance characteristics, it is built the ARM-designed 16/32-bit ARM7TDMI processor can execute 32-bit ARM instructions, but also perform 16-bit THUMB instructions, and integrates several external components. S3C4510B system clock frequency to 50MHz, 8 kB of Cache / SRAM, 4MB of Flash for storage of boot code, embedded operating system and application software. The management module in the design, S3C4510B through the system bus is connected with an FPGA chip XC2S30. XC2S30 and dual-channel VoSLAC (Voiceover broadband Subscriber Line Audio? ProcessingCircuit) chip Le78D11 connected, Le78D11 and dual-channel VoSLAC chip Le77D11 connected two analog subscriber line extended out the RJ11 interface for connection of two analog telephone. S3C4510B two UART, one with audio and video decoding module cross-connect serial cable to provide a simulation of the SLIP link; another UART MAX232 extended through a DB9 interface for the control of the terminal management module interface, the interface debugging and fault detection system is useful. S3C4510B with JTAG interface for system debugging and FLASH programming online simulation and so on.

Absolute, gauge and differential pressures – zero reference

Although pressure is an absolute quantity, everyday pressure measurements, such as for tire pressure, are usually made relative to ambient air pressure. In other cases measurements are made relative to a vacuum or to some other ad hoc reference. When distinguishing between these zero references, the following terms are used:

Absolute pressure is zero referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric pressure.

Gauge pressure is zero referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure. Negative signs are usually omitted.

Differential pressure is the difference in pressure between two points.

The zero reference in use is usually implied by context, and these words are only added when clarification is needed. Tire pressure and blood pressure are gauge pressures by convention, while atmospheric pressures, deep vacuum pressures, and altimeter pressures must be absolute. Differential pressures are commonly used in industrial process systems. Differential pressure gauges have two inlet ports, each connected to one of the volumes whose pressure is to be monitored. In effect, such a gauge performs the mathematical operation of subtraction through mechanical means, obviating the need for an operator or control system to watch two separate gauges and determine the difference in readings. Moderate vacuum pressures are often ambiguous, as they may represent absolute pressure or gauge pressure without a negative sign. Thus a vacuum of 26 inHg gauge is equivalent to an absolute pressure of 30 inHg (typical atmospheric pressure) 26 inHg = 4 inHg.

Atmospheric pressure is typically about 100 kPa at sea level, but is variable with altitude and weather. If the absolute pressure of a fluid stays constant, the gauge pressure of the same fluid will vary as atmospheric pressure changes. For example, when a car drives up a mountain, the tire pressure goes up. Some standard values of atmospheric pressure such as 101.325 kPa or 100 kPa have been defined, and some instruments use one of these standard values as a constant zero reference instead of the actual variable ambient air pressure. This impairs the accuracy of these instruments, especially when used at high altitudes.

Use of the atmosphere as reference is usually signified by a (g) after the pressure unit e.g. 30 psi g, which means that the pressure measured is the total pressure minus atmospheric pressure. There are two types of gauge reference pressure: vented gauge (vg) and sealed gauge (sg).

A vented gauge pressure transmitter for example allows the outside air pressure to be exposed to the negative side of the pressure sensing diaphragm, via a vented cable or a hole on the side of the device, so that it always measures the pressure referred to ambient barometric pressure. Thus a vented gauge reference pressure sensor should always read zero pressure when the process pressure connection is held open to the air.

A sealed gauge reference is very similar except that atmospheric pressure is sealed on the negative side of the diaphragm. This is usually adopted on high pressure ranges such as hydraulics where atmospheric pressure changes will have a negligible effect on the accuracy of the reading, so venting is not necessary. This also allows some manufacturers to provide secondary pressure containment as an extra precaution for pressure equipment safety if the burst pressure of the primary pressure sensing diaphragm is exceeded.

There is another way of creating a sealed gauge reference and this is to seal a high vacuum on the reverse side of the sensing diaphragm. Then the output signal is offset so the pressure sensor reads close to zero when measuring atmospheric pressure.

A sealed gauge reference pressure transducer will never read exactly zero because atmospheric pressure is always changing and the reference in this case is fixed at 1 bar.

An absolute pressure measurement is one that is referred to absolute vacuum. The best example of an absolute referenced pressure is atmospheric or barometric pressure.

To produce an absolute pressure sensor the manufacturer will seal a high vacuum behind the sensing diaphragm. If the process pressure connection of an absolute pressure transmitter is open to the air, it will read the actual barometric pressure.

Units

Pressure Units

 

pascal

(Pa)

bar

(bar)

technical atmosphere

(at)

atmosphere

(atm)

torr

(Torr)

pound-force per

square inch

(psi)

1 Pa

1 N/m2

105

1.0197105

9.8692106

7.5006103

145.04106

1 bar

100,000

106 dyn/cm2

1.0197

0.98692

750.06

14.5037744

1 at

98,066.5

0.980665

1 kgf/cm2

0.96784

735.56

14.223

1 atm

101,325

1.01325

1.0332

1 atm

760

14.696

1 torr

133.322

1.3332103

1.3595103

1.3158103

1 Torr;  1 mmHg

19.337103

1 psi

6.894103

68.948103

70.307103

68.046103

51.715

1 lbf/in2

Example reading:  1 Pa = 1 N/m2  = 105 bar  = 10.197106 at  = 9.8692106 atm, etc.

The SI unit for pressure is the pascal (Pa), equal to one newton per square metre (Nm2 or kgm1s2). This special name for the unit was added in 1971; before that, pressure in SI was expressed in units such as N/m. When indicated, the zero reference is stated in parenthesis following the unit, for example 101 kPa (abs). The pound per square inch (psi) is still in widespread use in the US and Canada, notably for cars. A letter is often appended to the psi unit to indicate the measurement’s zero reference; psia for absolute, psig for gauge, psid for differential, although this practice is discouraged by the NIST .

Because pressure was once commonly measured by its ability to displace a column of liquid in a manometer, pressures are often expressed as a depth of a particular fluid (e.g. inches of water). The most common choices are mercury (Hg) and water; water is nontoxic and readily available, while mercury’s density allows for a shorter column (and so a smaller manometer) to measure a given pressure.

Fluid density and local gravity can vary from one reading to another depending on local factors, so the height of a fluid column does not define pressure precisely. When ‘millimetres of mercury’ or ‘inches of mercury’ are quoted today, these units are not based on a physical column of mercury; rather, they have been given precise definitions that can be expressed in terms of SI units. The water-based units usually assume one of the older definitions of the kilogram as the weight of a litre of water.

Although no longer favoured by measurement experts, these manometric units are still encountered in many fields. Blood pressure is measured in millimetres of mercury in most of the world, and lung pressures in centimeters of water are still common. Natural gas pipeline pressures are measured in inches of water, expressed as ‘”WC’ (‘Water Column’). Scuba divers often use a manometric rule of thumb: the pressure exerted by ten metres depth of water is approximately equal to one atmosphere. In vacuum systems, the units torr, micrometre of mercury (micron), and inch of mercury (inHg) are most commonly used. Torr and micron usually indicates an absolute pressure, while inHg usually indicates a gauge pressure.

Atmospheric pressures are usually stated using kilopascal (kPa), or atmospheres (atm), except in American meteorology where the hectopascal (hPa) and millibar (mbar) are preferred. In American and Canadian engineering, stress is often measured in kip. Note that stress is not a true pressure since it is not scalar. In the cgs system the unit of pressure was the barye (ba), equal to 1 dyncm2. In the mts system, the unit of pressure was the pieze, equal to 1 sthene per square metre.

Many other hybrid units are used such as mmHg/cm or grams-force/cm (sometimes as kg/cm and g/mol2 without properly identifying the force units). Using the names kilogram, gram, kilogram-force, or gram-force (or their symbols) as a unit of force is forbidden in SI; the unit of force in SI is the newton (N).

Static and Dynamic pressure

Static pressure is uniform in all directions, so pressure measurements are independent of direction in an immovable (static) fluid. Flow, however, applies additional pressure on surfaces perpendicular to the flow direction, while having little impact on surfaces parallel to the flow direction. This directional component of pressure in a moving (dynamic) fluid is called dynamic pressure. An instrument facing the flow direction measures the sum of the static and dynamic pressures; this measurement is called the total pressure or stagnation pressure. Since dynamic pressure is referenced to static pressure, it is neither gauge nor absolute; it is a differential pressure.

While static gauge pressure is of primary importance to determining net loads on pipe walls, dynamic pressure is used to measure flow rates and airspeed. Dynamic pressure can be measured by taking the differential pressure between instruments parallel and perpendicular to the flow. Pitot-static tubes, for example perform this measurement on airplanes to determine airspeed. The presence of the measuring instrument inevitably acts to divert flow and create turbulence, so its shape is critical to accuracy and the calibration curves are often non-linear.

Applications

Altimeter

Barometer

MAP sensor

Pitot tube

Sphygmomanometer

Instruments

Many instruments have been invented to measure pressure, with different advantages and disadvantages. Pressure range, sensitivity, dynamic response and cost all vary by several orders of magnitude from one instrument design to the next. The oldest type is the liquid column (a vertical tube filled with mercury) manometer invented by Evangelista Torricelli in 1643. The U-Tube was invented by Christian Huygens in 1661.

Hydrostatic

Hydrostatic gauges (such as the mercury column manometer) compare pressure to the hydrostatic force per unit area at the base of a column of fluid. Hydrostatic gauge measurements are independent of the type of gas being measured, and can be designed to have a very linear calibration. They have poor dynamic response.

Piston

Piston-type gauges counterbalance the pressure of a fluid with a solid weight or a spring. Another name for piston gauge is deadweight tester. For example, dead-weight testers used for calibration or tire-pressure gauges.

Liquid column

The difference in fluid height in a liquid column manometer is proportional to the pressure difference.
Liquid column gauges consist of a vertical column of liquid in a tube whose ends are exposed to different pressures. The column will rise or fall until its weight is in equilibrium with the pressure differential between the two ends of the tube. A very simple version is a U-shaped tube half-full of liquid, one side of which is connected to the region of interest while the reference pressure (which might be the atmospheric pressure or a vacuum) is applied to the other. The difference in liquid level represents the applied pressure. The pressure exerted by a column of fluid of height h and density is given by the hydrostatic pressure equation, P = hg. Therefore the pressure difference between the applied pressure Pa and the reference pressure P0 in a U-tube manometer can be found by solving Pa P0 = hg. If the fluid being measured is significantly dense, hydrostatic corrections may have to be made for the height between the moving surface of the manometer working fluid and the location where the pressure measurement is desired.

Although any fluid can be used, mercury is preferred for its high density (13.534 g/cm3) and low vapour pressure. For low pressure differences well above the vapour pressure of water, water is commonly used (and “inches of water” is a common pressure unit). Liquid-column pressure gauges are independent of the type of gas being measured and have a highly linear calibration. They have poor dynamic response. When measuring vacuum, the working liquid may evaporate and contaminate the vacuum if its vapor pressure is too high. When measuring liquid pressure, a loop filled with gas or a light fluid must isolate the liquids to prevent them from mixing. Simple hydrostatic gauges can measure pressures ranging from a few Torr (a few 100 Pa) to a few atmospheres. (Approximately 1,000,000 Pa)

A single-limb liquid-column manometer has a larger reservoir instead of one side of the U-tube and has a scale beside the narrower column. The column may be inclined to further amplify the liquid movement. Based on the use and structure following type of manometers are used

Simple Manometer

Micromanometer

Differential manometer

Inverted differential manometer

A McLeod gauge, drained of mercury

McLeod gauge

A McLeod gauge isolates a sample of gas and compresses it in a modified mercury manometer until the pressure is a few mmHg. The gas must be well-behaved during its compression (it must not condense, for example). The technique is slow and unsuited to continual monitoring, but is capable of good accuracy.

Useful range: above 10-4 torr (roughly 10-2 Pa) as high as 106 Torr (0.1 mPa),

0.1 mPa is the lowest direct measurement of pressure that is possible with current technology. Other vacuum gauges can measure lower pressures, but only indirectly by measurement of other pressure-controlled properties. These indirect measurements must be calibrated to SI units via a direct measurement, most commonly a McLeod gauge.

Aneroid

Aneroid gauges are based on a metallic pressure sensing element which flexes elastically under the effect of a pressure difference across the element. “Aneroid” means “without fluid,” and the term originally distinguished these gauges from the hydrostatic gauges described above. However, aneroid gauges can be used to measure the pressure of a liquid as well as a gas, and they are not the only type of gauge that can operate without fluid. For this reason, they are often called mechanical gauges in modern language. Aneroid gauges are not dependent on the type of gas being measured, unlike thermal and ionization gauges, and are less likely to contaminate the system than hydrostatic gauges. The pressure sensing element may be a Bourdon tube, a diaphragm, a capsule, or a set of bellows, which will change shape in response to the pressure of the region in question. The deflection of the pressure sensing element may be read by a linkage connected to a needle, or it may be read by a secondary transducer. The most common secondary transducers in modern vacuum gauges measure a change in capacitance due to the mechanical deflection. Gauges that rely on a change in capacitances are often referred to as Baratron gauges.

Bourdon

Membrane-type manometer

A Bourdon gauge uses a coiled tube, which, as it expands due to pressure increase causes a rotation of an arm connected to the tube. In 1849 the Bourdon tube pressure gauge was patented in France by Eugene Bourdon.

The pressure sensing element is a closed coiled tube connected to the chamber or pipe in which pressure is to be sensed. As the gauge pressure increases the tube will tend to uncoil, while a reduced gauge pressure will cause the tube to coil more tightly. This motion is transferred through a linkage to a gear train connected to an indicating needle. The needle is presented in front of a card face inscribed with the pressure indications associated with particular needle deflections. In a barometer, the Bourdon tube is sealed at both ends and the absolute pressure of the ambient atmosphere is sensed. Differential Bourdon gauges use two Bourdon tubes and a mechanical linkage that compares the readings.

In the following illustrations the transparent cover face of the pictured combination pressure and vacuum gauge has been removed and the mechanism removed from the case. This particular gauge is a combination vacuum and pressure gauge used for automotive diagnosis:

Indicator side with card and dial

Mechanical side with Bourdon tube

the left side of the face, used for measuring manifold vacuum, is calibrated in centimetres of mercury on its inner scale and inches of mercury on its outer scale.

the right portion of the face is used to measure fuel pump pressure and is calibrated in fractions of 1 kgf/cm on its inner scale and pounds per square inch on its outer scale.

Mechanical details

Mechanical details

Stationary parts:

A: Receiver block. This joins the inlet pipe to the fixed end of the Bourdon tube (1) and secures the chassis plate (B). The two holes receive screws that secure the case.

B: Chassis plate. The face card is attached to this. It contains bearing holes for the axles.

C: Secondary chassis plate. It supports the outer ends of the axles.

D: Posts to join and space the two chassis plates.

Moving Parts:

Stationary end of Bourdon tube. This communicates with the inlet pipe through the receiver block.

Moving end of Bourdon tube. This end is sealed.

Pivot and pivot pin.

Link joining pivot pin to lever (5) with pins to allow joint rotation.

Lever. This an extension of the sector gear (7).

Sector gear axle pin.

Sector gear.

Indicator needle axle. This has a spur gear that engages the sector gear (7) and extends through the face to drive the indicator needle. Due to the short distance between the lever arm link boss and the pivot pin and the difference between the effective radius of the sector gear and that of the spur gear, any motion of the Bourdon tube is greatly amplified. A small motion of the tube results in a large motion of the indicator needle.

Hair spring to preload the gear train to eliminate gear lash and hysteresis.

Diaphragm

A pile of pressure capsules with corrugated diaphragms in an aneroid barograph.

A second type of aneroid gauge uses the deflection of a flexible membrane that separates regions of different pressure. The amount of deflection is repeatable for known pressures so the pressure can be determined by using calibration. The deformation of a thin diaphragm is dependent on the difference in pressure between its two faces. The reference face can be open to atmosphere to measure gauge pressure, open to a second port to measure differential pressure, or can be sealed against a vacuum or other fixed reference pressure to measure absolute pressure. The deformation can be measured using mechanical, optical or capacitive techniques. Ceramic and metallic diaphragms are used.

Useful range: above 10-2 Torr (roughly 1 Pa)

For absolute measurements, welded pressure capsules with diaphragms on either side are often used.

Shape:

Flat

corrugated

flattened tube

capsule

Bellows

In gauges intended to sense small pressures or pressure differences, or require that an absolute pressure be measured, the gear train and needle may be driven by an enclosed and sealed bellows chamber, called an aneroid, which means “without liquid”. (Early barometers used a column of liquid such as water or the liquid metal mercury suspended by a vacuum.) This bellows configuration is used in aneroid barometers (barometers with an indicating needle and dial card), altimeters, altitude recording barographs, and the altitude telemetry instruments used in weather balloon radiosondes. These devices use the sealed chamber as a reference pressure and are driven by the external pressure. Other sensitive aircraft instruments such as air speed indicators and rate of climb indicators (variometers) have connections both to the internal part of the aneroid chamber and to an external enclosing chamber.

Electronic pressure sensors

Main article: Pressure sensor

Piezoresistive Strain Gage

Uses the piezoresistive effect of bonded or formed strain gauges to detect strain due to applied pressure.

Capacitive

Uses a diaphragm and pressure cavity to create a variable capacitor to detect strain due to applied pressure.

Magnetic

Measures the displacement of a diaphragm by means of changes in inductance (reluctance), LVDT, Hall Effect, or by eddy current principal.

Piezoelectric

Uses the piezoelectric effect in certain materials such as quartz to measure the strain upon the sensing mechanism due to pressure.

Optical

Uses the physical change of an optical fiber to detect strain due applied pressure.

Potentiometric

Uses the motion of a wiper along a resistive mechanism to detect the strain caused by applied pressure.

Resonant

Uses the changes in resonant frequency in a sensing mechanism to measure stress, or changes in gas density, caused by applied pressure.

Thermal conductivity

Generally, as a real gas increases in density -which may indicate an increase in pressure- its ability to conduct heat increases. In this type of gauge, a wire filament is heated by running current through it. A thermocouple or Resistance Temperature Detector (RTD) can then be used to measure the temperature of the filament. This temperature is dependent on the rate at which the filament loses heat to the surrounding gas, and therefore on the thermal conductivity. A common variant is the Pirani gauge which uses a single platinum filament as both the heated element and RTD. These gauges are accurate from 10 Torr to 103 Torr, but they are sensitive to the chemical composition of the gases being measured.

Two wire

One wire coil is used as a heater, and the other is used to measure nearby temperature due to convection.

Pirani (one wire)

A Pirani gauge consists of a metal wire open to the pressure being measured. The wire is heated by a current flowing through it and cooled by the gas surrounding it. If the gas pressure is reduced, the cooling effect will decrease, hence the equilibrium temperature of the wire will increase. The resistance of the wire is a function of its temperature: by measuring the voltage across the wire and the current flowing through it, the resistance (and so the gas pressure) can be determined. This type of gauge was invented by Marcello Pirani.

Thermocouple gauges and thermistor gauges work in a similar manner, except a thermocouple or thermistor is used to measure the temperature of the wire.

Useful range: 10-3 – 10 Torr (roughly 10-1 – 1000 Pa)

Ionization gauge

Ionization gauges are the most sensitive gauges for very low pressures (also referred to as hard or high vacuum). They sense pressure indirectly by measuring the electrical ions produced when the gas is bombarded with electrons. Fewer ions will be produced by lower density gases. The calibration of an ion gauge is unstable and dependent on the nature of the gases being measured, which is not always known. They can be calibrated against a McLeod gauge which is much more stable and independent of gas chemistry.

Thermionic emission generate electrons, which collide with gas atoms and generate positive ions. The ions are attracted to a suitably biased electrode known as the collector. The current in the collector is proportional to the rate of ionization, which is a function of the pressure in the system. Hence, measuring the collector current gives the gas pressure. There are several sub-types of ionization gauge.

Useful range: 10-10 – 10-3 torr (roughly 10-8 – 10-1 Pa)

Most ion gauges come in two types: hot cathode and cold cathode, a third type exists which is more sensitive and expensive known as a spinning rotor gauge, but is not discussed here. In the hot cathode version an electrically heated filament produces an electron beam. The electrons travel through the gauge and ionize gas molecules around them. The resulting ions are collected at a negative electrode. The current depends on the number of ions, which depends on the pressure in the gauge. Hot cathode gauges are accurate from 103 Torr to 1010 Torr. The principle behind cold cathode version is the same, except that electrons are produced in a discharge created by a high voltage electrical discharge. Cold Cathode gauges are accurate from 102 Torr to 109 Torr. Ionization gauge calibration is very sensitive to construction geometry, chemical composition of gases being measured, corrosion and surface deposits. Their calibration can be invalidated by activation at atmospheric pressure or low vacuum. The composition of gases at high vacuums will usually be unpredictable, so a mass spectrometer must be used in conjunction with the ionization gauge for accurate measurement.

Hot cathode

Bayard-Alpert hot cathode ionization gauge

A hot cathode ionization gauge is mainly composed of three electrodes all acting as a triode, where the cathode is the filament. The three electrodes are a collector or plate, a filament, and a grid. The collector current is measured in picoamps by an electrometer. The filament voltage to ground is usually at a potential of 30 volts while the grid voltage at 180210 volts DC, unless there is an optional electron bombardment feature, by heating the grid which may have a high potential of approximately 565 volts. The most common ion gauge is the hot cathode Bayard-Alpert gauge, with a small ion collector inside the grid. A glass envelope with an opening to the vacuum can surround the electrodes, but usually the Nude Gauge is inserted in the vacuum chamber directly, the pins being fed through a ceramic plate in the wall of the chamber. Hot cathode gauges can be damaged or lose their calibration if they are exposed to atmospheric pressure or even low vacuum while hot. The measurements of a hot cathode ionization gauge are always logarithmic.

Electrons emitted from the filament move several times in back and forth movements around the grid before finally entering the grid. During these movements, some electrons collide with a gaseous molecule to form a pair of an ion and an electron (Electron ionization). The number of these ions is proportional to the gaseous molecule density multiplied by the electron current emitted from the filament, and these ions pour into the collector to form an ion current. Since the gaseous molecule density is proportional to the pressure, the pressure is estimated by measuring the ion current.

The low pressure sensitivity of hot cathode gauges is limited by the photoelectric effect. Electrons hitting the grid produce x-rays that produce photoelectric noise in the ion collector. This limits the range of older hot cathode gauges to 108 Torr and the Bayard-Alpert to about 1010 Torr. Additional wires at cathode potential in the line of sight between the ion collector and the grid prevent this effect. In the extraction type the ions are not attracted by a wire, but by an open cone. As the ions cannot decide which part of the cone to hit, they pass through the hole and form an ion beam. This ion beam can be passed on to a

Faraday cup

Microchannel plate detector with Faraday cup

Quadrupole mass analyzer with Faraday cup

Quadrupole mass analyzer with Microchannel plate detector Faraday cup

ion lens and acceleration voltage and directed at a target to form a sputter gun. In this case a valve lets gas into the grid-cage.

See also: Electron ionization

Cold cathode

There are two subtypes of cold cathode ionization gauges: the Penning gauge (invented by Frans Michel Penning), and the Inverted magnetron, also called a Redhead gauge. The major difference between the two is the position of the anode with respect to the cathode. Neither has a filament, and each may require a DC potential of about 4 kV for operation. Inverted magnetrons can measure down to 1×1012 Torr.

Such gauges cannot operate if the ions generated by the cathode recombine before reaching the anodes. If the mean-free path of the gas within the gauge is smaller than the gauge’s dimensions, then the electrode current will essentially vanish. A practical upper-bound to the detectable pressure is, for a Penning gauge, of the order of 103 Torr.

Similarly, cold cathode gauges may be reluctant to start at very low pressures, in that the near-absence of a gas makes it difficult to establish an electrode current – particularly in Penning gauges which use an axially symmetric magnetic field to create path lengths for ions which are of the order of metres. In ambient air suitable ion-pairs are ubiquitously formed by cosmic radiation; in a Penning gauge design features are used to ease the set-up of a discharge path. For example, the electrode of a Penning gauge is usually finely tapered to facilitate the field emission of electrons.

Maintenance cycles of cold cathode gauges is generally measured in years, depending on the gas type and pressure that they are operated in. Using a cold cathode gauge in gases with substantial organic components, such as pump oil fractions, can result in the growth of delicate carbon films and shards within the gauge which eventually either short-circuit the electrodes of the gauge, or impede the generation of a discharge path.

Calibration

Pressure gauges are either direct- or indirect-reading. Hydrostatic and elastic gauges measure pressure are directly influenced by force exerted on the surface by incident particle flux, and are called direct reading gauges. Thermal and ionization gauges read pressure indirectly by measuring a gas property that changes in a predictable manner with gas density. Indirect measurements are susceptible to more errors than direct measurements.

Dead weight tester

McLeod

mass spec + ionization

Dynamic transients

When fluid flows are not in equilibrium, local pressures may be higher or lower than the average pressure in a medium. These disturbances propagate from their source as longitudinal pressure variations along the path of propagation. This is also called sound. Sound pressure is the instantaneous local pressure deviation from the average pressure caused by a sound wave. Sound pressure can be measured using a microphone in air and a hydrophone in water. The effective sound pressure is the root mean square of the instantaneous sound pressure over a given interval of time. Sound pressures are normally small and are often expressed in units of microbar.

frequency response of pressure sensors

resonance

History

Further information: Timeline of temperature and pressure measurement technology

European (CEN) Standard

EN 472 : Pressure gauge – Vocabulary.

EN 837-1 : Pressure gauges. Bourdon tube pressure gauges. Dimensions, metrology, requirements and testing.

EN 837-2 : Pressure gauges. Selection and installation recommendations for pressure gauges.

EN 837-3 : Pressure gauges. Diaphragm and capsule pressure gauges. Dimensions, metrology, requirements and testing..

See also

Force gauge

Piezometer

Vacuum engineering

External links

Home Made Manometer

Manometer

References

^ NIST

^ [Was: "fluidengineering.co.nr/Manometer.htm". At 1/2010 that took me to bad link. Types of fluid Manometers]

^ Techniques of high vacuum

^ Beckwith, Thomas G.; Roy D. Marangoni and John H. Lienhard V (1993). “Measurement of Low Pressures”. Mechanical Measurements (Fifth ed.). Reading, MA: Addison-Wesley. pp. 591595. ISBN 0-201-56947-7. 

^ Product brochure from Schoonover, Inc

^ VG Scienta

^ Robert M. Besanon, ed (1990). “Vacuum Techniques” (3rd edition ed.). Van Nostrand Reinhold, New York. pp. 12781284. ISBN 0-442-00522-9. 

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Categories: Underwater diving | Vacuum | Pressure gauges | Measuring instruments

Absolute, gauge and differential pressures – zero reference

Although pressure is an absolute quantity, everyday pressure measurements, such as for tire pressure, are usually made relative to ambient air pressure. In other cases measurements are made relative to a vacuum or to some other ad hoc reference. When distinguishing between these zero references, the following terms are used:

Absolute pressure is zero referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric pressure.

Gauge pressure is zero referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure. Negative signs are usually omitted.

Differential pressure is the difference in pressure between two points.

The zero reference in use is usually implied by context, and these words are only added when clarification is needed. Tire pressure and blood pressure are gauge pressures by convention, while atmospheric pressures, deep vacuum pressures, and altimeter pressures must be absolute. Differential pressures are commonly used in industrial process systems. Differential pressure gauges have two inlet ports, each connected to one of the volumes whose pressure is to be monitored. In effect, such a gauge performs the mathematical operation of subtraction through mechanical means, obviating the need for an operator or control system to watch two separate gauges and determine the difference in readings. Moderate vacuum pressures are often ambiguous, as they may represent absolute pressure or gauge pressure without a negative sign. Thus a vacuum of 26 inHg gauge is equivalent to an absolute pressure of 30 inHg (typical atmospheric pressure) 26 inHg = 4 inHg.

Atmospheric pressure is typically about 100 kPa at sea level, but is variable with altitude and weather. If the absolute pressure of a fluid stays constant, the gauge pressure of the same fluid will vary as atmospheric pressure changes. For example, when a car drives up a mountain, the tire pressure goes up. Some standard values of atmospheric pressure such as 101.325 kPa or 100 kPa have been defined, and some instruments use one of these standard values as a constant zero reference instead of the actual variable ambient air pressure. This impairs the accuracy of these instruments, especially when used at high altitudes.

Use of the atmosphere as reference is usually signified by a (g) after the pressure unit e.g. 30 psi g, which means that the pressure measured is the total pressure minus atmospheric pressure. There are two types of gauge reference pressure: vented gauge (vg) and sealed gauge (sg).

A vented gauge pressure transmitter for example allows the outside air pressure to be exposed to the negative side of the pressure sensing diaphragm, via a vented cable or a hole on the side of the device, so that it always measures the pressure referred to ambient barometric pressure. Thus a vented gauge reference pressure sensor should always read zero pressure when the process pressure connection is held open to the air.

A sealed gauge reference is very similar except that atmospheric pressure is sealed on the negative side of the diaphragm. This is usually adopted on high pressure ranges such as hydraulics where atmospheric pressure changes will have a negligible effect on the accuracy of the reading, so venting is not necessary. This also allows some manufacturers to provide secondary pressure containment as an extra precaution for pressure equipment safety if the burst pressure of the primary pressure sensing diaphragm is exceeded.

There is another way of creating a sealed gauge reference and this is to seal a high vacuum on the reverse side of the sensing diaphragm. Then the output signal is offset so the pressure sensor reads close to zero when measuring atmospheric pressure.

A sealed gauge reference pressure transducer will never read exactly zero because atmospheric pressure is always changing and the reference in this case is fixed at 1 bar.

An absolute pressure measurement is one that is referred to absolute vacuum. The best example of an absolute referenced pressure is atmospheric or barometric pressure.

To produce an absolute pressure sensor the manufacturer will seal a high vacuum behind the sensing diaphragm. If the process pressure connection of an absolute pressure transmitter is open to the air, it will read the actual barometric pressure.

Units

Pressure Units

 

pascal

(Pa)

bar

(bar)

technical atmosphere

(at)

atmosphere

(atm)

torr

(Torr)

pound-force per

square inch

(psi)

1 Pa

1 N/m2

105

1.0197105

9.8692106

7.5006103

145.04106

1 bar

100,000

106 dyn/cm2

1.0197

0.98692

750.06

14.5037744

1 at

98,066.5

0.980665

1 kgf/cm2

0.96784

735.56

14.223

1 atm

101,325

1.01325

1.0332

1 atm

760

14.696

1 torr

133.322

1.3332103

1.3595103

1.3158103

1 Torr;  1 mmHg

19.337103

1 psi

6.894103

68.948103

70.307103

68.046103

51.715

1 lbf/in2

Example reading:  1 Pa = 1 N/m2  = 105 bar  = 10.197106 at  = 9.8692106 atm, etc.

The SI unit for pressure is the pascal (Pa), equal to one newton per square metre (Nm2 or kgm1s2). This special name for the unit was added in 1971; before that, pressure in SI was expressed in units such as N/m. When indicated, the zero reference is stated in parenthesis following the unit, for example 101 kPa (abs). The pound per square inch (psi) is still in widespread use in the US and Canada, notably for cars. A letter is often appended to the psi unit to indicate the measurement’s zero reference; psia for absolute, psig for gauge, psid for differential, although this practice is discouraged by the NIST .

Because pressure was once commonly measured by its ability to displace a column of liquid in a manometer, pressures are often expressed as a depth of a particular fluid (e.g. inches of water). The most common choices are mercury (Hg) and water; water is nontoxic and readily available, while mercury’s density allows for a shorter column (and so a smaller manometer) to measure a given pressure.

Fluid density and local gravity can vary from one reading to another depending on local factors, so the height of a fluid column does not define pressure precisely. When ‘millimetres of mercury’ or ‘inches of mercury’ are quoted today, these units are not based on a physical column of mercury; rather, they have been given precise definitions that can be expressed in terms of SI units. The water-based units usually assume one of the older definitions of the kilogram as the weight of a litre of water.

Although no longer favoured by measurement experts, these manometric units are still encountered in many fields. Blood pressure is measured in millimetres of mercury in most of the world, and lung pressures in centimeters of water are still common. Natural gas pipeline pressures are measured in inches of water, expressed as ‘”WC’ (‘Water Column’). Scuba divers often use a manometric rule of thumb: the pressure exerted by ten metres depth of water is approximately equal to one atmosphere. In vacuum systems, the units torr, micrometre of mercury (micron), and inch of mercury (inHg) are most commonly used. Torr and micron usually indicates an absolute pressure, while inHg usually indicates a gauge pressure.

Atmospheric pressures are usually stated using kilopascal (kPa), or atmospheres (atm), except in American meteorology where the hectopascal (hPa) and millibar (mbar) are preferred. In American and Canadian engineering, stress is often measured in kip. Note that stress is not a true pressure since it is not scalar. In the cgs system the unit of pressure was the barye (ba), equal to 1 dyncm2. In the mts system, the unit of pressure was the pieze, equal to 1 sthene per square metre.

Many other hybrid units are used such as mmHg/cm or grams-force/cm (sometimes as kg/cm and g/mol2 without properly identifying the force units). Using the names kilogram, gram, kilogram-force, or gram-force (or their symbols) as a unit of force is forbidden in SI; the unit of force in SI is the newton (N).

Static and Dynamic pressure

Static pressure is uniform in all directions, so pressure measurements are independent of direction in an immovable (static) fluid. Flow, however, applies additional pressure on surfaces perpendicular to the flow direction, while having little impact on surfaces parallel to the flow direction. This directional component of pressure in a moving (dynamic) fluid is called dynamic pressure. An instrument facing the flow direction measures the sum of the static and dynamic pressures; this measurement is called the total pressure or stagnation pressure. Since dynamic pressure is referenced to static pressure, it is neither gauge nor absolute; it is a differential pressure.

While static gauge pressure is of primary importance to determining net loads on pipe walls, dynamic pressure is used to measure flow rates and airspeed. Dynamic pressure can be measured by taking the differential pressure between instruments parallel and perpendicular to the flow. Pitot-static tubes, for example perform this measurement on airplanes to determine airspeed. The presence of the measuring instrument inevitably acts to divert flow and create turbulence, so its shape is critical to accuracy and the calibration curves are often non-linear.

Applications

Altimeter

Barometer

MAP sensor

Pitot tube

Sphygmomanometer

Instruments

Many instruments have been invented to measure pressure, with different advantages and disadvantages. Pressure range, sensitivity, dynamic response and cost all vary by several orders of magnitude from one instrument design to the next. The oldest type is the liquid column (a vertical tube filled with mercury) manometer invented by Evangelista Torricelli in 1643. The U-Tube was invented by Christian Huygens in 1661.

Hydrostatic

Hydrostatic gauges (such as the mercury column manometer) compare pressure to the hydrostatic force per unit area at the base of a column of fluid. Hydrostatic gauge measurements are independent of the type of gas being measured, and can be designed to have a very linear calibration. They have poor dynamic response.

Piston

Piston-type gauges counterbalance the pressure of a fluid with a solid weight or a spring. Another name for piston gauge is deadweight tester. For example, dead-weight testers used for calibration or tire-pressure gauges.

Liquid column

The difference in fluid height in a liquid column manometer is proportional to the pressure difference.
Liquid column gauges consist of a vertical column of liquid in a tube whose ends are exposed to different pressures. The column will rise or fall until its weight is in equilibrium with the pressure differential between the two ends of the tube. A very simple version is a U-shaped tube half-full of liquid, one side of which is connected to the region of interest while the reference pressure (which might be the atmospheric pressure or a vacuum) is applied to the other. The difference in liquid level represents the applied pressure. The pressure exerted by a column of fluid of height h and density is given by the hydrostatic pressure equation, P = hg. Therefore the pressure difference between the applied pressure Pa and the reference pressure P0 in a U-tube manometer can be found by solving Pa P0 = hg. If the fluid being measured is significantly dense, hydrostatic corrections may have to be made for the height between the moving surface of the manometer working fluid and the location where the pressure measurement is desired.

Although any fluid can be used, mercury is preferred for its high density (13.534 g/cm3) and low vapour pressure. For low pressure differences well above the vapour pressure of water, water is commonly used (and “inches of water” is a common pressure unit). Liquid-column pressure gauges are independent of the type of gas being measured and have a highly linear calibration. They have poor dynamic response. When measuring vacuum, the working liquid may evaporate and contaminate the vacuum if its vapor pressure is too high. When measuring liquid pressure, a loop filled with gas or a light fluid must isolate the liquids to prevent them from mixing. Simple hydrostatic gauges can measure pressures ranging from a few Torr (a few 100 Pa) to a few atmospheres. (Approximately 1,000,000 Pa)

A single-limb liquid-column manometer has a larger reservoir instead of one side of the U-tube and has a scale beside the narrower column. The column may be inclined to further amplify the liquid movement. Based on the use and structure following type of manometers are used

Simple Manometer

Micromanometer

Differential manometer

Inverted differential manometer

A McLeod gauge, drained of mercury

McLeod gauge

A McLeod gauge isolates a sample of gas and compresses it in a modified mercury manometer until the pressure is a few mmHg. The gas must be well-behaved during its compression (it must not condense, for example). The technique is slow and unsuited to continual monitoring, but is capable of good accuracy.

Useful range: above 10-4 torr (roughly 10-2 Pa) as high as 106 Torr (0.1 mPa),

0.1 mPa is the lowest direct measurement of pressure that is possible with current technology. Other vacuum gauges can measure lower pressures, but only indirectly by measurement of other pressure-controlled properties. These indirect measurements must be calibrated to SI units via a direct measurement, most commonly a McLeod gauge.

Aneroid

Aneroid gauges are based on a metallic pressure sensing element which flexes elastically under the effect of a pressure difference across the element. “Aneroid” means “without fluid,” and the term originally distinguished these gauges from the hydrostatic gauges described above. However, aneroid gauges can be used to measure the pressure of a liquid as well as a gas, and they are not the only type of gauge that can operate without fluid. For this reason, they are often called mechanical gauges in modern language. Aneroid gauges are not dependent on the type of gas being measured, unlike thermal and ionization gauges, and are less likely to contaminate the system than hydrostatic gauges. The pressure sensing element may be a Bourdon tube, a diaphragm, a capsule, or a set of bellows, which will change shape in response to the pressure of the region in question. The deflection of the pressure sensing element may be read by a linkage connected to a needle, or it may be read by a secondary transducer. The most common secondary transducers in modern vacuum gauges measure a change in capacitance due to the mechanical deflection. Gauges that rely on a change in capacitances are often referred to as Baratron gauges.

Bourdon

Membrane-type manometer

A Bourdon gauge uses a coiled tube, which, as it expands due to pressure increase causes a rotation of an arm connected to the tube. In 1849 the Bourdon tube pressure gauge was patented in France by Eugene Bourdon.

The pressure sensing element is a closed coiled tube connected to the chamber or pipe in which pressure is to be sensed. As the gauge pressure increases the tube will tend to uncoil, while a reduced gauge pressure will cause the tube to coil more tightly. This motion is transferred through a linkage to a gear train connected to an indicating needle. The needle is presented in front of a card face inscribed with the pressure indications associated with particular needle deflections. In a barometer, the Bourdon tube is sealed at both ends and the absolute pressure of the ambient atmosphere is sensed. Differential Bourdon gauges use two Bourdon tubes and a mechanical linkage that compares the readings.

In the following illustrations the transparent cover face of the pictured combination pressure and vacuum gauge has been removed and the mechanism removed from the case. This particular gauge is a combination vacuum and pressure gauge used for automotive diagnosis:

Indicator side with card and dial

Mechanical side with Bourdon tube

the left side of the face, used for measuring manifold vacuum, is calibrated in centimetres of mercury on its inner scale and inches of mercury on its outer scale.

the right portion of the face is used to measure fuel pump pressure and is calibrated in fractions of 1 kgf/cm on its inner scale and pounds per square inch on its outer scale.

Mechanical details

Mechanical details

Stationary parts:

A: Receiver block. This joins the inlet pipe to the fixed end of the Bourdon tube (1) and secures the chassis plate (B). The two holes receive screws that secure the case.

B: Chassis plate. The face card is attached to this. It contains bearing holes for the axles.

C: Secondary chassis plate. It supports the outer ends of the axles.

D: Posts to join and space the two chassis plates.

Moving Parts:

Stationary end of Bourdon tube. This communicates with the inlet pipe through the receiver block.

Moving end of Bourdon tube. This end is sealed.

Pivot and pivot pin.

Link joining pivot pin to lever (5) with pins to allow joint rotation.

Lever. This an extension of the sector gear (7).

Sector gear axle pin.

Sector gear.

Indicator needle axle. This has a spur gear that engages the sector gear (7) and extends through the face to drive the indicator needle. Due to the short distance between the lever arm link boss and the pivot pin and the difference between the effective radius of the sector gear and that of the spur gear, any motion of the Bourdon tube is greatly amplified. A small motion of the tube results in a large motion of the indicator needle.

Hair spring to preload the gear train to eliminate gear lash and hysteresis.

Diaphragm

A pile of pressure capsules with corrugated diaphragms in an aneroid barograph.

A second type of aneroid gauge uses the deflection of a flexible membrane that separates regions of different pressure. The amount of deflection is repeatable for known pressures so the pressure can be determined by using calibration. The deformation of a thin diaphragm is dependent on the difference in pressure between its two faces. The reference face can be open to atmosphere to measure gauge pressure, open to a second port to measure differential pressure, or can be sealed against a vacuum or other fixed reference pressure to measure absolute pressure. The deformation can be measured using mechanical, optical or capacitive techniques. Ceramic and metallic diaphragms are used.

Useful range: above 10-2 Torr (roughly 1 Pa)

For absolute measurements, welded pressure capsules with diaphragms on either side are often used.

Shape:

Flat

corrugated

flattened tube

capsule

Bellows

In gauges intended to sense small pressures or pressure differences, or require that an absolute pressure be measured, the gear train and needle may be driven by an enclosed and sealed bellows chamber, called an aneroid, which means “without liquid”. (Early barometers used a column of liquid such as water or the liquid metal mercury suspended by a vacuum.) This bellows configuration is used in aneroid barometers (barometers with an indicating needle and dial card), altimeters, altitude recording barographs, and the altitude telemetry instruments used in weather balloon radiosondes. These devices use the sealed chamber as a reference pressure and are driven by the external pressure. Other sensitive aircraft instruments such as air speed indicators and rate of climb indicators (variometers) have connections both to the internal part of the aneroid chamber and to an external enclosing chamber.

Electronic pressure sensors

Main article: Pressure sensor

Piezoresistive Strain Gage

Uses the piezoresistive effect of bonded or formed strain gauges to detect strain due to applied pressure.

Capacitive

Uses a diaphragm and pressure cavity to create a variable capacitor to detect strain due to applied pressure.

Magnetic

Measures the displacement of a diaphragm by means of changes in inductance (reluctance), LVDT, Hall Effect, or by eddy current principal.

Piezoelectric

Uses the piezoelectric effect in certain materials such as quartz to measure the strain upon the sensing mechanism due to pressure.

Optical

Uses the physical change of an optical fiber to detect strain due applied pressure.

Potentiometric

Uses the motion of a wiper along a resistive mechanism to detect the strain caused by applied pressure.

Resonant

Uses the changes in resonant frequency in a sensing mechanism to measure stress, or changes in gas density, caused by applied pressure.

Thermal conductivity

Generally, as a real gas increases in density -which may indicate an increase in pressure- its ability to conduct heat increases. In this type of gauge, a wire filament is heated by running current through it. A thermocouple or Resistance Temperature Detector (RTD) can then be used to measure the temperature of the filament. This temperature is dependent on the rate at which the filament loses heat to the surrounding gas, and therefore on the thermal conductivity. A common variant is the Pirani gauge which uses a single platinum filament as both the heated element and RTD. These gauges are accurate from 10 Torr to 103 Torr, but they are sensitive to the chemical composition of the gases being measured.

Two wire

One wire coil is used as a heater, and the other is used to measure nearby temperature due to convection.

Pirani (one wire)

A Pirani gauge consists of a metal wire open to the pressure being measured. The wire is heated by a current flowing through it and cooled by the gas surrounding it. If the gas pressure is reduced, the cooling effect will decrease, hence the equilibrium temperature of the wire will increase. The resistance of the wire is a function of its temperature: by measuring the voltage across the wire and the current flowing through it, the resistance (and so the gas pressure) can be determined. This type of gauge was invented by Marcello Pirani.

Thermocouple gauges and thermistor gauges work in a similar manner, except a thermocouple or thermistor is used to measure the temperature of the wire.

Useful range: 10-3 – 10 Torr (roughly 10-1 – 1000 Pa)

Ionization gauge

Ionization gauges are the most sensitive gauges for very low pressures (also referred to as hard or high vacuum). They sense pressure indirectly by measuring the electrical ions produced when the gas is bombarded with electrons. Fewer ions will be produced by lower density gases. The calibration of an ion gauge is unstable and dependent on the nature of the gases being measured, which is not always known. They can be calibrated against a McLeod gauge which is much more stable and independent of gas chemistry.

Thermionic emission generate electrons, which collide with gas atoms and generate positive ions. The ions are attracted to a suitably biased electrode known as the collector. The current in the collector is proportional to the rate of ionization, which is a function of the pressure in the system. Hence, measuring the collector current gives the gas pressure. There are several sub-types of ionization gauge.

Useful range: 10-10 – 10-3 torr (roughly 10-8 – 10-1 Pa)

Most ion gauges come in two types: hot cathode and cold cathode, a third type exists which is more sensitive and expensive known as a spinning rotor gauge, but is not discussed here. In the hot cathode version an electrically heated filament produces an electron beam. The electrons travel through the gauge and ionize gas molecules around them. The resulting ions are collected at a negative electrode. The current depends on the number of ions, which depends on the pressure in the gauge. Hot cathode gauges are accurate from 103 Torr to 1010 Torr. The principle behind cold cathode version is the same, except that electrons are produced in a discharge created by a high voltage electrical discharge. Cold Cathode gauges are accurate from 102 Torr to 109 Torr. Ionization gauge calibration is very sensitive to construction geometry, chemical composition of gases being measured, corrosion and surface deposits. Their calibration can be invalidated by activation at atmospheric pressure or low vacuum. The composition of gases at high vacuums will usually be unpredictable, so a mass spectrometer must be used in conjunction with the ionization gauge for accurate measurement.

Hot cathode

Bayard-Alpert hot cathode ionization gauge

A hot cathode ionization gauge is mainly composed of three electrodes all acting as a triode, where the cathode is the filament. The three electrodes are a collector or plate, a filament, and a grid. The collector current is measured in picoamps by an electrometer. The filament voltage to ground is usually at a potential of 30 volts while the grid voltage at 180210 volts DC, unless there is an optional electron bombardment feature, by heating the grid which may have a high potential of approximately 565 volts. The most common ion gauge is the hot cathode Bayard-Alpert gauge, with a small ion collector inside the grid. A glass envelope with an opening to the vacuum can surround the electrodes, but usually the Nude Gauge is inserted in the vacuum chamber directly, the pins being fed through a ceramic plate in the wall of the chamber. Hot cathode gauges can be damaged or lose their calibration if they are exposed to atmospheric pressure or even low vacuum while hot. The measurements of a hot cathode ionization gauge are always logarithmic.

Electrons emitted from the filament move several times in back and forth movements around the grid before finally entering the grid. During these movements, some electrons collide with a gaseous molecule to form a pair of an ion and an electron (Electron ionization). The number of these ions is proportional to the gaseous molecule density multiplied by the electron current emitted from the filament, and these ions pour into the collector to form an ion current. Since the gaseous molecule density is proportional to the pressure, the pressure is estimated by measuring the ion current.

The low pressure sensitivity of hot cathode gauges is limited by the photoelectric effect. Electrons hitting the grid produce x-rays that produce photoelectric noise in the ion collector. This limits the range of older hot cathode gauges to 108 Torr and the Bayard-Alpert to about 1010 Torr. Additional wires at cathode potential in the line of sight between the ion collector and the grid prevent this effect. In the extraction type the ions are not attracted by a wire, but by an open cone. As the ions cannot decide which part of the cone to hit, they pass through the hole and form an ion beam. This ion beam can be passed on to a

Faraday cup

Microchannel plate detector with Faraday cup

Quadrupole mass analyzer with Faraday cup

Quadrupole mass analyzer with Microchannel plate detector Faraday cup

ion lens and acceleration voltage and directed at a target to form a sputter gun. In this case a valve lets gas into the grid-cage.

See also: Electron ionization

Cold cathode

There are two subtypes of cold cathode ionization gauges: the Penning gauge (invented by Frans Michel Penning), and the Inverted magnetron, also called a Redhead gauge. The major difference between the two is the position of the anode with respect to the cathode. Neither has a filament, and each may require a DC potential of about 4 kV for operation. Inverted magnetrons can measure down to 1×1012 Torr.

Such gauges cannot operate if the ions generated by the cathode recombine before reaching the anodes. If the mean-free path of the gas within the gauge is smaller than the gauge’s dimensions, then the electrode current will essentially vanish. A practical upper-bound to the detectable pressure is, for a Penning gauge, of the order of 103 Torr.

Similarly, cold cathode gauges may be reluctant to start at very low pressures, in that the near-absence of a gas makes it difficult to establish an electrode current – particularly in Penning gauges which use an axially symmetric magnetic field to create path lengths for ions which are of the order of metres. In ambient air suitable ion-pairs are ubiquitously formed by cosmic radiation; in a Penning gauge design features are used to ease the set-up of a discharge path. For example, the electrode of a Penning gauge is usually finely tapered to facilitate the field emission of electrons.

Maintenance cycles of cold cathode gauges is generally measured in years, depending on the gas type and pressure that they are operated in. Using a cold cathode gauge in gases with substantial organic components, such as pump oil fractions, can result in the growth of delicate carbon films and shards within the gauge which eventually either short-circuit the electrodes of the gauge, or impede the generation of a discharge path.

Calibration

Pressure gauges are either direct- or indirect-reading. Hydrostatic and elastic gauges measure pressure are directly influenced by force exerted on the surface by incident particle flux, and are called direct reading gauges. Thermal and ionization gauges read pressure indirectly by measuring a gas property that changes in a predictable manner with gas density. Indirect measurements are susceptible to more errors than direct measurements.

Dead weight tester

McLeod

mass spec + ionization

Dynamic transients

When fluid flows are not in equilibrium, local pressures may be higher or lower than the average pressure in a medium. These disturbances propagate from their source as longitudinal pressure variations along the path of propagation. This is also called sound. Sound pressure is the instantaneous local pressure deviation from the average pressure caused by a sound wave. Sound pressure can be measured using a microphone in air and a hydrophone in water. The effective sound pressure is the root mean square of the instantaneous sound pressure over a given interval of time. Sound pressures are normally small and are often expressed in units of microbar.

frequency response of pressure sensors

resonance

History

Further information: Timeline of temperature and pressure measurement technology

European (CEN) Standard

EN 472 : Pressure gauge – Vocabulary.

EN 837-1 : Pressure gauges. Bourdon tube pressure gauges. Dimensions, metrology, requirements and testing.

EN 837-2 : Pressure gauges. Selection and installation recommendations for pressure gauges.

EN 837-3 : Pressure gauges. Diaphragm and capsule pressure gauges. Dimensions, metrology, requirements and testing..

See also

Force gauge

Piezometer

Vacuum engineering

External links

Home Made Manometer

Manometer

References

^ NIST

^ [Was: "fluidengineering.co.nr/Manometer.htm". At 1/2010 that took me to bad link. Types of fluid Manometers]

^ Techniques of high vacuum

^ Beckwith, Thomas G.; Roy D. Marangoni and John H. Lienhard V (1993). “Measurement of Low Pressures”. Mechanical Measurements (Fifth ed.). Reading, MA: Addison-Wesley. pp. 591595. ISBN 0-201-56947-7. 

^ Product brochure from Schoonover, Inc

^ VG Scienta

^ Robert M. Besanon, ed (1990). “Vacuum Techniques” (3rd edition ed.). Van Nostrand Reinhold, New York. pp. 12781284. ISBN 0-442-00522-9. 

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