We know that pressure sensors are the most common sensors in industrial practice and are widely used in various industrial automation applications. There are many different types of sensors and different areas of application.

Introduction to strain gauge sensors

There are many different types of pressure sensors, such as resistive strain gauge pressure sensors, semiconductor strain gauge pressure sensors, piezoresistive pressure sensors, pressure sensors, capacitive pressure sensors, resonant pressure sensors and diaphragm electrode pressure sensors. However, the most widely used is the resistive strain gauge pressure sensor, which has a very low price, high accuracy and good linearity. It consists of a base material, a metal strain wire or strain foil, an insulating protective sheet and a lead wire. Depending on the application, the resistance of the strain gauges can be designed by the designer, but the range of resistance values should be noted: too small a resistance requires too much driving current, while the heating of the strain gauges causes the temperature of the gauges themselves to be too high for use in different environments, making the resistance of the gauges vary too much, the output zero point drift is obvious and the zeroing circuit is too complex. The resistance is too large and the impedance is too high, making it less resistant to external electromagnetic interference. Generally, they are tens to tens of kilo-ohms.

What is a strain gauge pressure sensor?

A strain gauge pressure sensor is a pressure sensor that uses an elastic sensitive element and a strain gauge to convert the measured pressure into a corresponding change in resistance.

How strain gauge sensors work

A resistance-strain gauge pressure sensor is a combination of a measurement circuit consisting of a resistance-strain gauge and an elastic sensitive element. When the elastic sensitive element is subjected to pressure, a strain is generated and the strain is also generated by the resistive strain gauges affixed to the surface, which is expressed as a change in resistance. The deformation of the elastomer is thus translated into a change in the resistance value of the resistive strain gauges. By connecting the four strain gauges in a bridge circuit and applying a certain voltage value to the two inputs, the common mode voltage at the two outputs increases or decreases with the change in resistance value on the bridge circuit. Generally the correspondence of this variation has an approximately linear relationship. By finding the correspondence between the change in pressure and the change in output common-mode voltage, the pressure value can be obtained by measuring the common-mode voltage.

Working principle of strain gauge pressure sensors

The principle of operation of a strain gauge is the change in resistance of a strain resistor on a base material in response to mechanical deformation, commonly referred to as the resistive strain effect. The resistance of a metallic conductor can be expressed by the following equation:

Where: ρ - the resistivity of the metal conductor (Ω. cm2/m )

S - the cross-sectional area of the conductor (cm2 )

L - the length of the conductor (m)

Let us take the example of wire strain resistance, when the wire is subjected to an external force, its length and cross-sectional area will change.

If the wire is stretched by an external force, its length increases and the cross-sectional area decreases, the resistance value will increase. When the wire is compressed by an external force, the length decreases and the cross-sectional area increases, the resistance value decreases. The strain on a strained wire can be obtained by measuring the change in resistance (usually by measuring the voltage across the resistance).