Pressure instruments may use mechanical sensing elements such as Bourdon tubes, bellows, or diaphragms. These elements are mechanically connected to an indicator, recorder, controller, or transmitter.
Electronic pressure transmitters, on the other hand, have sensing elements such as resonant wires, strain gages, capacitors, and piezoelectric crystals that convert pressure into an electronic output signal. Specific techniques are often proprietary. The Company has not established a preference.
Field pressure switches (see Section 417) may use Bourdon tube, bellows, diaphragm, spring piston, or spring disk sensors. Spring disk pressure switches are preferred for most applications.
The following descriptions and comparisons for different sensing methods are for information only. In practice, the design engineer may have little or no say over the type of element that the manufacturer has utilized for the selected instrument. However, it may sometimes be necessary for a measurement to be performed that requires a specific type of sensing element. In this case it is important to know the differences between various instruments.