03/01/2025
Strain Gauge Applications - Part 2
Tension, compression, shear and torsional stresses can be measured with strain gauges by accurately determining the actual material strain or deformation.
Strain gauges are constructed from resistive material that exhibits linear change in resistance with respect to deformation. Most strain gauges are able to linearly measure deformation within 2-3% of strain, or 0.02 strain units.
Careful arrangement of multiple gauges in wheatstone circuit, called wheatstone bridge, gives measurable output voltage corresponds to the change in resistance. Changes of fraction of ohms produce millivolts of signal to be measured with sensitive data acquisition systems.
imc Data Acquisition Systems are equipped with internal bridge completion, sense wiring and 24 bit delta-sigma analog to digital conversion to obtain highly accurate strain measurements.
Since wheatstone bridge output is proportionate to the input voltage, the data acquisition system requires to have capability to measure the voltage ratio in mV/V (output mV / input Voltage) rather than the output signal alone.
Arrangement of strain gauges in the placement and wiring determines which deformation is to be measured, axial, bending or both. For Torsional strain measurement, gauges with 45 degree pattern are used.
Direct application of Wheatstone bridge would normally involve 4 strain gauges. It may be difficult to realize if the strain directions need to be evaluated with rosettes. Only one gauge will be active and remaining 3 being dummy or idle with only benefit of thermal compensation.
This situation is circumvented by use of quarter bridge and providing cmpletion resistances inside the measurement system. Thermal compensation is not ideal, but a good compromise on gauge and installation cost
The picture attached shows typical wiring for quarter bridge, the picture is taken from imc Studio Software, to be used with imc DCB bridge amplifiers for Cronos series. imc ARGUSfit series has double sense and a bit different wiring method.
Stay tuned for our next parts for discussion on other types of wiring.