OPTIMAL-DESIGN OF ELECTRICAL SUBSTITUTION RADIOMETERS WITH FEEDBACK-CONTROL

The response behaviour of feedback-controlled radiometers has been analysed in order to understand how to design the control system and take measurements with the least measurement time for a given variance or vice versa. For "single-observation" measurements, in which the response is observed only once after settling for each shutter movement, solutions are obtained for the third-order system comprising integral plus proportional control and a first-order filter. Using expressions developed for the variance in the mean of a sequence of partially correlated observations, the analysis is extended to "repeated-observation" measurements which are averages of sequences of observations taken after settling for each shutter movement. Numerical analysis of one simple system shows that there is an optimal number of observations and control system design for any set of values of detector noise level, desired measurement variance, and sampling frequency.