DYNAMIC-RESPONSE OF A FEEDBACK THERMORESISTIVE ELECTRICAL SUBSTITUTION PYRANOMETER

Calorimetric pyranometers use plane black thermal sensors which absorb solar radiation. If a thermoresistive transducer (sensor-detector com bination) is used, the temperature measured is nearer the tote value t han for thermoelectric transducers. More importantly, the measurement of electrical power is much more accurate than the measurement of temp erature. In commercial platinum (thermoresistive), thin film thermomet ers, the substrate produces transducer time constants an order of magn itude larger than for the best thermoelectric transducers. Use of an e lectronic amplifier with the thermoresistive sensor, forming one ann o f a Wheatstone bridge and arranged in a negative feedback configuratio n, can reduce the overall response time considerably. Theoretical form ulations of instrument response, taking into account the amplifier inp ut offset voltage, are presented and the response time is estimated.