Pressure Sensor Measurement Theory

Pressure Sensor Measurement Theory

The pressure measurement system is made up of a sensing element with four strain gauges applied to it. The strain gauges are configured in a Wheatstone bridge, where all 4 resistors (labeled R1 thru R4 in Figure 2) are equal, and change by equal magnitude proportionally, when strain is applied. The greater the force or strain (input), the greater the output. A Wheatstone bridge device requires 4 wires for its connection, positive and negative excitation, and positive and negative sensor output.

A typical pressure sensor works producing a strain gauge output as the deflection of a diaphragm is caused. Depending on the strain gauge technology the output can vary from 1 to 3 millivolts per volt (mV/V) to as much as 10 to 30 mV/V. To calculate your full scale output, you would multiply the output of the sensor by the voltage used to power the device. For example, for a 3 mV/V sensor, if we used 10 volts DC as our excitation voltage, we would expect to get 3 mV/V x 10V=30 mV at full scale.