This is the general term for controls that use compressed air as the motive force for control inputs and output, instead of electricity. Analog pneumatic pressures are alternately coded and de-coded into control units; for example: 3-15 psig = 0-100 degF. Discrete pneumatic pressures are also coded; for example, 0 psig = off, 20 psig = on. Pneumatic devices can be two-state or modulating, but are most commonly modulating. Pneumatic controls often have interface devices that communicate pneumatic signals to and from their electric counterparts, such as Pressure-to-Electric switches (PE switches), and various Electric-to-Pneumatic solenoids and transducers. Some considerations for pneumatic controls:

• Air supply quality is critical. No oil or water allowed at the instruments!

• Contamination in the main air system represents a potential single point of failure for many or all pneumatic controls.

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