A gas pressure comparator is normally used for calibrating at relatively lower pressures. It’s main benefit is cleanliness. If the device being tested is used in a process that doesn’t tolerate liquid contaminants, then you’ll probably want to use a gas pressure comparator.
Most gas pressure comparators allow you to adjust and regulate the supply pressure, either through a pump or a needle valve. Pump-based gas pressure comparators like the Fluke Calibration P5510 are best suited for pressures below 2 MPa (300 psi). A pump has the advantage of not requiring an external gas supply, allowing you to use the comparator in more applications. The drawback is that you have to pump harder to get higher pressures, and your hands and arms can get tired.
For pressures above 2 MPa (300 psi) that still require gas media, many users find it easier to use a pressure comparator that meters in pressure from an external supply. To enable the supplied gas to be metered precisely, fine needle valves control both the gas supply into the system and the gas exhaust out of the system.
The pressure comparator may also use a variable volume to allow for small changes in pressure. This can be used to make fine adjustments so that either the reference gauge or
devices under test are reading on the cardinal point. The Fluke Calibration P5513 is a good example of this type of pressure comparator. Whereas a pump based gas pressure comparator is limited by the force the operator can apply, this type of comparator is limited only by the maximum working pressure of the internal components and the pressure of the supply gas.
Features to look for in a gas pressure comparator
- Test port connections. Using a pressure comparator to calibrate a device requires that both a reference gauge and a device under test to be connected to the comparator. If your normal workload includes gauges with a wide variety of pressure ranges and connection types, then choose a type of connection that allows you to quickly switch out the reference gauge, and one that can easily handle the types of connections you normally see in your lab.
- Pressure pump. Pressure pumps are ideal for pressures of 2 MPa (300 psi) and below. If you are working with higher pressures, you probably should consider another pressure generation method.
- Fine adjustment. If your procedure requires fine adjustment of the pressure at the test point, then make sure the comparator has the ability to provide fine adjustment and is sufficient for your application.
- Pressure supply connection. For higher pressure applications where a connection to supply pressure is feasible, consider pressure comparators that can make use of that supply pressure versus manual pumps. Your technicians will thank you for it.
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Source: Application Note: How to Choose a Pressure Comparator