From Sensor Technology Handbook

19.1 Introduction to Strain Gages

Dr. Thomas Kenny, Department of Mechanical Engineering, Stanford University

Strain gages are used in many types of sensors. They provide a convenient way to convert a displacement (strain) into an electrical signal. Their output is actually a change of resistance. It can be converted to a voltage signal by connecting the strain gage(s) in a bridge configuration. A few sensors use only a single strain gage element in the bridge, along with three fixed resistors. Others use two strain gages and two fixed resistors, and most recent designs use four strain gages. The gages may be almost any material, but some materials are much more efficient strain gages than others. Proprietary metal alloys and semiconductor silicon are the most commonly used materials.


A piezoresistor is a device that exhibits a change in resistance when it is strained. There are two components of the piezoresistive effect in most materials the geometric component and the resistive component.

Figure 19.1.1: Liquid strain gage: mercury tube.

The geometric component of piezoresistivity comes from the fact that a strained element undergoes a change in dimension. These changes in cross-sectional area and length affect the resistance of the device.

A good example of the geometric effect of piezoresistivity is the liquid strain gage. A great many of these devices were in use years ago. Imagine an elastic tube filled with a conductive fluid, such as mercury. The resistance of the mercury in the tube can be measured with a pair of...

Products & Services
Digital Pressure Gauges
Digital pressure gauges use electronic components to convert applied pressure into usable signals. The gauge readout has a digital numerical display.
Strain Gauges
Strain gauges are measuring elements that convert force, pressure, tension, etc., into an electrical signal.
Bore and ID Gages
Bore and ID gages are designed for internal diameter dimensional measurement or assessment.
Vacuum Gauges and Instruments
Vacuum gauges are devices for measuring vacuum or sub-atmospheric pressures.
Pressure Sensors
Pressure sensors include all sensors, transducers and elements that produce an electrical signal proportional to pressure or changes in pressure.

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