Dynamic Response of a Feedback Thermoresistive Electrical Substitution Pyranometer

Abstract

Calorimetric pyranometers use plane black thermal sensors which absorb solar radiation. If a thermoresistive transducer (sensor-detector combination) is used, the temperature measured is nearer the true value than for thermoelectric transducers. More importantly, the measurement of electrical power is much more accurate than the measurement of temperature. In commercial platinum (thermoresistive), thin film thermometers, the substrate produces transducer time constants an order of magnitude larger than for the best thermoelectric transducers. Use of an electronic amplifier with the thermoresistive sensor, forming one arm of a Wheatstone bridge and arranged in a negative feedback configuration, can reduce the overall response time considerably. Theoretical formulations of instrument response, taking into account the amplifier input offset voltage, are presented and the response time is estimated.