Performance Metric
Ratio of the change in output voltage to the change in temperature for a resistive network defines the thermal stability of a bridge circuit. The wheatstone bridge temperature coefficient accounts for the shifts in both the zero balance and the span sensitivity of the sensor until the operating limit of the compensation components is reached.
Source Error
Mismatched resistance changes in the individual arms of the circuit produce an unintended signal offset. Even when using precision resistors, the wheatstone bridge temperature coefficient is affected by the thermal expansion of the substrate and the strain sensitivity of the traces. Passive compensation involves placing thermistors or wire resistors in the circuit to cancel these effects.
Calibration Procedure
Evaluation of the bridge involves heating the entire assembly in a controlled chamber while monitoring the output at zero load. The wheatstone bridge temperature coefficient is expressed in parts per million per degree Celsius. Modern digital sensors use software algorithms to correct for this drift based on a local temperature reading.
Design Limit
High performance transducers require a very low thermal error to maintain accuracy in field conditions. A wheatstone bridge temperature coefficient that is too large will mask the actual physical signal being measured.
