Thursday, May 5, 2016

Electromechanical Pressure, Differential Pressure and Temperature Switches - The Basics

Many industrial applications require the monitoring or control of pressure and temperature of a process. Pressure and temperature measurement can be accomplished either by transmitters, gauges, or switches. This post will provide a quick introduction to industrial electromechanical pressure switches and temperature switches.

Pressure Switch

An industrial pressure switch is made up of three main components:
  1. The sensor
  2. The housing
  3. The switching element.
Industrial process control pressure switch
Pressure Switch








Switching Element

The switching element refers to the signaling device inside the enclosure that responds to the movement of the sensor. It can be either electrical or pneumatic, and provides an on-off signal based upon the switch setpoint (as opposed to an analog, or proportional signal produced by transmitters).


For the switching element and the sensor, it is very important to know the cycling rate (number switch state changes per unit of time) the instrument will see. Since both of these elements are mechanical, they will eventually wear out and need to be replaced. Switches are an economical and strong performing choice for low to medium cycle rates. For extremely high cycle rates, the use of solid state transmitters is a better choice.

Temperature Switches

An electromechanical temperature switch (sometimes called a thermostat) is, for the most part, a piston type pressure switch connected to a filled capillary and bulb sensing element. The thermal expansion of the media inside the bulb and capillary creates the pressure and linear movement upon the piston sensor of the switch. The bulb and capillary elements are often supplied in copper or stainless steel, and at various lengths.

There are many more details to selecting and applying electromechanical pressure and temperature switches. This post provides a very general introduction. It is always suggested to discuss your application with a qualified applications engineer so that you are assured to get the longest lasting, most economical and safest instrument possible.