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:
- Sensor bridge output signal Vo
- 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
- Sensor Load Calibration
Acromag is a leading manufacturer of signal transmitters and conditioners. Our products can be used with many types of process sensors that will generally amplify and isolate the sensor signal and convert it to a proportional current or voltage output, or Modbus, Profibus, Ethernet message for interface to a PC, PLC, DCS, or other control equipment.
Acromag has designed and manufactured measurement and control products for more than 60 years. We are an AS9100 and ISO 9001-certified international corporation headquartered near Detroit, Michigan, and serve a global network of sales representatives and distributors. Acromag offers a complete line of industrial I/O products, including; a variety of process instruments, signal conditioners, and distributed fieldbus I/O modules, all available with a 2-year warranty. Industries served include chemical processing, manufacturing, defense, energy, and water services
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