# Introduction to Strain Gauge Transmitters and Strain Measurement – 8500699

## Introduction to Strain Gauge and Strain Measurement

This paper discusses strain gauge and load cell input transmitters and strain and load measurement, as related to Acromag strain modules and transmitters in particular. However, the principles may be extended to other strain gauge or load cell instruments as well.

Strain gauges change resistance in proportion to applied forces as a result of 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.

A bridge can be wired in several ways:

• One active strain gauge and three resistors (quarter bridge)
• Two active strain gauges and two resistors (half-bridge)
• Four active strain gauges (full-bridge)

The number of active gauges in a bridge, in addition to how they are oriented relative to applied force, determine; the bridge type, its application, and relative strain computation.

Strain is a measure of the mechanical deformation of a material, and computed as a fractional change in dimension; length, width, or height, resulting from a force
along that dimension. Strain may be positive or negative, and the magnitude of deformation it represents is a very small percentage; thus, it’s often expressed as an integer multiple of 10-6, or microstrain.

There are normally two sensor measurements used to resolve strain or load:

1. Sensor bridge output signal Vo
2. Sensor bridge excitation Vex

Using sensor specifications and these two measurements, the applied strain or load can be resolved from the bridge output signal.

### Topics Covered:

• Strain Gauge
• Strain Measurement
• Wheatstone Bridge
• Strain Bridge Equations
• Example Calculations for a Strain Gauge
• Example Calculations for a Load Cell
• Shunt-Calibration of a Strain Gauge Bridge