Pressure control may either control (maintain the pressure of gas, liquid, or solid at some specified value) or limit (sense that pressure has reached some preset limit or is moving out of some safe range). Pressure is defined as the force per unit area. The most common units of pressure are pounds per square inch (psi), inches of water column (wc) in a manometer, or inches of mercury (Hg). The most popular metric unit of measurement is the kilo-pascal (kPa).
Pressure is one of the most important industrial process variables. A normally closed pressure switch contact that opens on rising pressure is used. This pressure switch operates to signal the return of the pneumatic (air) cylinder. The advantage of using pressure switch over a limit switch is that the workpiece will always receive the same amount of pressure before the cylinder returns. The pressure switch is used to transfer information concerning pressure to an electric circuit.
Important pressure switch specifications include :
- Adjustable operating range
- Adjustable differential range
- Set point repeatability
- Enclosure type
- Electrical rating
- Switch arrangement
Figure 1.1 Pressure Control Switch
References :
Petruzella (1996). Industrial Electronics.Singapore: McGraw Hill.
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