Pressure Sensors

There are various kinds of sensor that respond to pressure:

Pressure switches have a mechanical or electronic contact that provides a binary (on/off) output signal depending on the pressure applied (is the pressure greater or less than a set value). The threshold can be fixed or adjustable. Such sensors are also called  pressure monitors.

Analog sensors, that provide an analog output depending on the applied pressure (usually a voltage).

Pressure Switches

Mechanically operating pressure switches respond to pressure acting on a piston in opposition to a spring. If the applied pressure overcomes the force of the spring, the piston moves and makes contact with a switch. Pressure switches are usually designed as changeover switches. The photgraph alongside shows a mechanical pressure switch as used in industry.

Electronic pressure switches mostly come in the form of membrane pressure switches nowadays. These make the contact for the changeover switch not mechanically but electronically. Pressure or force sensitive sensors are attached to a membrane and the sensor signal is processed by an electronic circuit that controls the changeover. The photograph to the right shows some membrane switches as used in industry.

The following graphic shows the circuit diagram symbol for a pressure switch (normally open in this case):

Analog Pressure Sensors

Analog pressure sensors usually provide an electrical output signal that is proportional to the applied pressure. They normally employ the so-called piezo effect . The photograph to the right shows an example of an analog pressure sensor as used in industry.

The following graphic shows the circuit diagram symbol for a pressure sensor that is functioning as a pressure-voltage converter, i.e. its output is a voltage proportional to the applied pressure:

A typical characteristic for an analog pressure sensor is shown in the graphic below. The output voltage of the sensor U is plotted against the pressure p. The characteristic indicates, for example, that the sensor output is 6 V when the pressure applied is 6 bars.