What is Strain Measurement an Introduction Technology Paper

What is Strain & Strain Measurement

What is Strain Gauge?Strain Gage Wheatstone Bridge Diagram

Strain gauges change resistance in proportion to applied forces that result from loading, torque, pressure, acceleration, and vibration. Because their change in resistance to force is very small, they often connect in a Wheatstone Bridge of four elements. You can wire a bridge with one active strain gauge and 3 resistors (quarter bridge), two active strain gauges and two resistors (half-bridge), or 4 active strain gauges (full-bridge). The number of active gauges in a bridge and how they are oriented relative to applied force will determine the bridge type, its application, and relative strain computation.

An “active” gauge is oriented in a direction to measure the effect of an applied force on a material (usually in the same direction as the force or lateral to it).

What is a Load Cell?

The load cell is a simpler form of a Wheatstone Bridge based sensor, but one whose output Vo is relative to percent of rated load and will correspond to the pressure or weight applied. Load cells are much simpler than strain gauge bridges because their relationship to load does not require additional detail of how its internal bridge elements are arranged, its Gauge Factor, or the Poisson’s ratio of the material it is applied to. The only important considerations for resolving the load cell are its rated output (mV/V), excitation voltage, and rated capacity.

Strain Measurement

There are normally two sensor measurements used to resolve strain or load: the sensor bridge output signal Vo and the sensor bridge excitation Vex. Using sensor specifications and these two measurements, the applied strain or load can be resolved from the bridge output signal.

Acromag’s TT351 is a Strain Gauge Input 4-Wire Transmitter

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