Method and apparatus for precision control of radiometer

A radiometer controller of a radiation detector is provided with a calibration method and apparatus comprised of mounting all temperature sensitive elements of the controller in thermostatically controlled ovens during calibration and measurements, using a selected temperature that is above any which might be reached in the field. The instrument is calibrated in situ by adjusting heater power (EI) to the receptor cavity in the radiometer detector to a predetermined full scale level as displayed by a meter. Then with the heater de-energized and the receptor cavity covered, the voltage output, (E /SUB o/ ) is set to zero as displayed by the meter. Next the preset power is applied to the heater and the output of the radiant measurement channel is applied to the panel meter. With this preset heater power producing the proper heat, the gain of the measurement channel is adjusted to bring the meter dispaly to full scale. The function switch is then set back to apply the measured radiant power signal to the meter. Once the radiation cavity is uncovered, radiant energy absorbed by the radiation cavity is displayed by the meter with an accuracy that heretofore has not been available. A reference voltage E /SUB R/ is used to calibrate the meter initially and at any time thereafter deemed necessary. To adjust the heater power to the predetermined full scale level, current and voltage values applied to the heater winding are separately derived from a bridge-like circuit connected between a source of heater power and ground, and applied to precision analog multiplier mounted in a thermostatically controlled oven