Pyroelectric and Photoelectric Detectors:

Pyroelectric Detectors:  these are temperature dependant capacitors made from a single crystalline wafer of a pyroelectric material, like as triglycerine sulphate.  The heating effect of incident IR radiation causes modify within the capacitance of the capacitor that in turn could be measured within the external circuit as current. Pyroelectric detectors have a quick response time to be able to respond to the signal from the interferometer. Thus they are used in most of the commercially available FT-IR instruments.

Photoelectric Transducers:  these are such as the mercury cadmium telluride transducers and comprise of a film of semiconducting material deposited on a glass surface that is sealed in an evacuated envelope. This is same to the photomultiplier tube given with dynodes in UV-VIS spectrophotometry.  Absorption of IR radiation through them causes the electrical resistance of the semiconductor to decrease that could be measured. These transducers have better response features than pyroelectric transducers, and also search use in FT-IR hyphenated instruments especially GC - FT-IR etc.