Air gauging and its applications have not change since its invention in the 1940s because the principle is built using the law of physics which remains constant. It is used to measure length. When you closed off an open-air jet, it builds up back pressure which can be easily graphed. Air gauging provides a pressure distance curve which can be used again for displacement measurement.
The most practical feature of air gauging is its pressure distance curve. The air tooling is comprised of a simple system: a precision cylinder with two open-air jets fed to a common channel. Restrictions are placed on the open-air jet resulting in pressure buildup which is then measured. In the 1940s, the principle of these two jets is understood by inventors as a necessity for differential measurement.
There are many types of air gauges which are classified using the basic principles of compressed air, namely, pressure and flow. Pressure gauges measure the back pressure as the size of the product changes while flow gauges measure the quantity of air that is coming through the circuit as the size of the product changes.
Each system has its own advantage and disadvantages. One of the most commonly used systems is the back-pressure-bleed because of its accuracy due to dual-master calibration. Another commonly used system is the differential because it is easy to use. There is no good or bad type of gauging, there are just different options and choices depend on the need of the person.
Air gauges are manufactured based on its application so there are different kinds available. The simplest is used to measure ID or OD by employing the open jets or even ball jets while the most complicated can measure a lot of attributes such as the flatness, thickness, taper, concentricity, plunjets and many more. These features are what determine how expensive the tool is. If it is able to read more and locate parts which are difficult to find then it is more expensive.
They are also classified into single and dual master. Its advantage among other type of gauges is the maintenance required. It needs less maintenance because it is simple, clean and only consists of few moving parts. The piece being measure is not touching the measuring surfaces and the air nozzle cleans the debris while measuring.