By using two detectors that are filtered to accept radiation in two independent adjacent windows of the spectrum, A1 and A2, an output voltage ratio can be obtained that is independent of the material emissivity. This is called two-color(ratio) infrared ther mometry. The output voltage of the ratio is defined as follows:
สมการ 14.13
This equation is usually solved by a microcomputer in the instrument that processes the incoming infrared radiation. The optical system that is associated with an instrument must be able to accurately define the area being observed. Because the response time of the sensors is considerably slower than a microprocessor, several transducers can be multiplexed by one controller(Fig. 14.29).