Characteristics of the Relatively Large Aparture Thermopile on Chopping Operation

Abstract

Very low frequency chopping operation of thermopile, which has relatively large aparture and time constant, has been studied and compared with dc mode.
Amplification of very low frequency (0.1-0.3 Hz) is carried out with a digital lock-in system and a usual dc amplifier.
Under chopping operation, apparent sensitivity falls with frequency increasing, but noise are also reduced, so detectivity at 0.2 Hz is 10⁷ W^-1cm Hz^-1/2, which is 1.2 times greater than dc mode. Drift free operation is realised with dc drift component cut off. Linearity and uniformity of receiving area are similar to dc mode.
Temperature coefficient of sensitivity has been improved and obtained value is-0.15%/°C at 19-29°C (about one half of that in dc mode).