How Does a Differential Pressure Sensor Sense Pressure?

Differential pressure sensors are typically packaged with two ports to which pipes can be attached. The pipes are then connected to the system where the measurement is to be made. Industrial pressure sensors may be integrated into a standardized fitting, allowing it to be built into existing pipework.

Typically, the two pressures to be measured are applied to opposite sides of a single diaphragm. The deflection of the diaphragm, either positive or negative with respect to the resting state, determines the difference in pressure. Some industrial differential pressure sensors actually use two separate absolute sensors, utilizing internal electronics to calculate and provide the difference in pressure to the control system.

This may be the case in situations where two different types of sensors are required due to the medium being measured, such as a liquid and a gas, or the environment of the measurement.

If required, a differential pressure measurement can be made using two absolute pressure sensors and software on the control system.

Many of the board-level sensors available utilize piezoresistive sensing elements. The simplest of these use a Wheatstone bridge configuration which requires a signal conditioning circuit to amplify its output.

An example circuit for amplifying the signal from a Wheatstone bridge piezoresistive pressure sensor.

Circuits like the above diagram apply a constant current to the bridge. The output signal is then amplified and applied to the input of the measurement system. If your application is based upon a micro controller, the signal could be connected to an ADC input pin. Otherwise, there are many standalone ADCs with digital outputs that could be sourced as an alternative.

The analog front end (AFE) may also need to allow provision for offset voltage, temperature compensation, and span. If you’re looking for a simpler solution, many manufacturers provide fully integrated differential sensors. For example, some may include temperature compensation circuitry together with two stages of amplification, enabling it to be simply connected to the ADC input of a micro controller.

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