Air gauges come in different variations of two basic principles of compressed air; pressure and flow. The pressure gauge monitors back pressure within a gaging circuit as the size of the product changes while the flow gauge monitors the amount of air that passes through a circuit as the product size changes. Each system has its advantages and disadvantages; however, the back-pressure-bleed system is one of the more popularly used because it’s inherent accuracy from a dual-master calibration routine. Another gauge that is also popular is the differential system because of its usability. There are air gauges for every application with some simple enough for lower-end applications. There are also gauges manufactured for more complicated applications that include measurement of tapers, flatness, concentricity, thickness and center distance. For high end applications, gauges usually include a special 6-inch diameter rifle-barrel twist air spindle with a 10-foot long connector that has the ability to measure a cannon bore.
There have been no considerable changes in the technology of air gauges over the past years but there have been upgrades in materials, coatings and processes. A piece of tooling manufactured in 1945 can be placed on a gauge built in 2006 and it will still function. The analog displays have not changed and they still use the same type of pressure-sensing mechanical device with the magnifier that will move the needle to display a change in length. However, an electronic readout has provided more information in an easy to read and understand format for the operator. When the gauges were combined with the power of microprocessors and computers, the pressure readings were easily converted to a display where the resolutions can be changed. The results can now be stored and data downloaded into a network system where it can be analyzed for process control.
One of the major advantages of the air gauge is maintenance because it is clean, simple and requires fewer moving parts. The measuring surfaces do not come into contact with the part that is being measured. The air nozzles help in cleaning any debris from the part that is being measured. There is also less risks for broken parts on the gauge because of the reduced mechanical apparatus. The more popular column-type amplifiers with the selectable range can be used for various tolerances. It is much easier to implement one type of amplifier that can accommodate various sizes and tolerances with consistency and it is less costly in the long run. Instead of buying another amplifier when a different tolerance has to be measured, a different range can simply be selected on the column gauge.