Caracterização de sensores termo-resistivos utilizando degrau de potência elétrica.

Abstract

The characterization of the dynamic response of a thermoresistive solar radiation sensor is important for adequately designing the radiation measuring instruments based on this sensor. This characterization implies the determination of the step-response of this sensor to termal energy excitation. The step response is monitored in term of the sensors temperature or its resistence. One can use calorimetric electrical methods for determing the time response of the sensor. In a purely electrical method me cam force a step change in the current throug the sensor to produce a sudden change in the thermal power (Joule effect) dissipated in the sensor. This current through the sensor is also used to monitor the resulting change in the sensor resistence. In another method the heating of the sensor is caused by incident radiation and the change in the sensor resistence is done electrically. In these methods an error is introduced in the time-response due to the change in the sensor heating caused by the varying sensor resistance. This error can be eliminated by applying electrically a .heat power step. This involves the constant adjustament of the sensor current to compensate for the variation in its resistance. A formulation of this methods is discussed and a microcontroler based configuration for practical implementation of this method is presented. Experimental results also presented.