Temperature compensation of force transducers with strain gages (DMS)

The temperature dependence of the measurement signal of strain gauge force transducers is caused by the following effects:

• Thermal expansion of the sensor body
• Temperature-dependent change in the strain gauge resistance
• Thermal expansion of the measuring grid foil of the strain gauge
• Temperature response of the connecting wires

To compensate for temperature effects, VELOMAT force transducers are connected as a strain gauge full bridge. This utilizes the effect that in the Wheatstone bridge circuit the strains of two strain gages with different signs contribute to the measurement signal and the temperature-dependent effects in the resulting bridge voltage largely compensate each other. A further improvement in compensation is achieved by using strain gauges that are matched to the thermal expansion coefficient of the sensor body (stainless steel or aluminum). These measures result in the following temperature errors for standard VELOMAT force transducers over the nominal temperature range (-15°C to +70°C):

Temperature error zero point < 0.04 % of final value /K

Temperature error sensitivity < 0.04 % of the final value /K

The remaining small residual error can be reduced by connecting temperature-dependent resistors in the measuring bridge and in the supply line to

Temperature error zero point < 0.004 % of the final value /K

Temperature error sensitivity < 0.004 % of the final value /K

can be improved. Complex measurements in the temperature cabinet are required to determine the resistance values.

Thermal equilibrium in the sensor is assumed for the error specifications. For example, one-sided heating of the sensor results in larger temperature errors due to the internal temperature gradient.