Thermodynamic modeling of a thermoresistive sensor using electrical power

A microcontroller-based electrical method to determine the intrinsic time constant of a thermoresistive sensor is described. The sudden change in the sensor heating with the change in the current or voltage introduces measurement errors and the value of time constant depends upon the final value of the current or voltage. Thus the sensor is supplied with an electrical power step and resulting resistance variation with time is monitored. The details of the feedback circuit to maintain the sensor power constant are described. The sensor structure under test behaved more like a second order system with one time constant three times larger than the other.