Apparatus and method for measuring temperatures at a plurality of

Abstract

A system for measuring a parameter, such as temperature, by multiple sensors that include luminescent material. A parameter dependent characteristic, such as decay time, of each sensor's luminescence radiation emitted in response to appropriate excitation, such as in the form of a pulse, is measured. Automatic gain control is provided by adjusting the duration of the excitation radiation pulses instead of their intensities. An undesired effect of excitation radiation directly striking the photodetector is minimized by subtracting a compensating signal from the photodetector output signal, that compensating signal being provided through a compensating photodetector connected in series with the luminescence receiving photodetector. Multiple sensors are handled by the electronic system through time division multiplexing, separate photodetectors provided for the sensors being connected in parallel while their associated sensors are excited to luminescence one at a time. An offset signal from the commonly connected photodetectors is measured in the absence of luminescence from any of the sensors and used to adjust the parameter dependent characteristic of each sensor's luminescent radiation.