Pressure Sensors

A pressure sensor measures the force exerted by a gas or liquid over an area and converts it into an electrical signal. Most designs use a thin diaphragm that deflects under applied pressure; the amount of deflection is detected and turned into a reading. Pressure can be measured in different reference modes: absolute pressure is referenced to a vacuum, gauge pressure to the surrounding atmosphere, and differential pressure to the difference between two ports.

The piezoresistive sensor is among the most widely used types. Resistive elements, often diffused or implanted into a silicon diaphragm, change their resistance when the diaphragm flexes and strains. These elements are arranged in a Wheatstone bridge so that the output voltage is proportional to the applied pressure while compensating for common effects such as temperature. The piezoresistive effect, in which mechanical strain alters a material's resistance, gives these devices good sensitivity and makes them suitable for mass production using semiconductor techniques.

Other approaches include capacitive sensors, where diaphragm movement changes the gap and hence the capacitance of a structure, and piezoelectric sensors, which suit rapidly changing or dynamic pressures. Strain gauges bonded to a diaphragm offer a similar principle to piezoresistive devices using metal foil elements. Pressure sensors are found throughout industry and everyday products, including engine management, weather instruments, medical equipment, hydraulic systems and altitude measurement.

Frequently asked questions

What is the difference between absolute and gauge pressure?

Absolute pressure is measured relative to a perfect vacuum, while gauge pressure is measured relative to the surrounding atmospheric pressure.

How does a piezoresistive pressure sensor work?

Pressure flexes a diaphragm carrying resistive elements; the resulting strain changes their resistance, and a Wheatstone bridge converts this into a proportional voltage.

Why are pressure sensors often built on silicon?

Silicon micromachining allows the diaphragm and piezoresistive elements to be made together with high precision and at low cost using semiconductor processes.