Spectrophotometer

Abstract

A spectrophotometer used for measurement of the transmittance of a sample according to an optical null method, wherein light from a light source is divided into two light beams and pass through a sample cell and reference cell respectively, chopped by a chopper for alternatively supplying the light beams through a monochrometer to a light detector providing signals which are amplified and subjected to synchronous detection by a synchronous rectifier operating in synchronism with the chopper operation so as to obtain an electric signal proportional to the intensity difference between the light passed through the sample cell and that passed through the reference cell with the intensity of the light passed through the reference cell being controlled by a light attenuator connected to a recording pen until the difference signal becomes null. The spectrophotometer further includes an AC signal source generating an AC signal in synchronous relation with the operation of the chopper for applying the AC signal to the input of the amplifier, a position-voltage transducer providing a signal representing the position of a recording pen, a voltage difference detector detecting the difference between the output voltages of the position-voltage transducer before and after the application of the AC signal, and a voltage variation rate detector detecting rate of transient variation with respect to time of the signal of the position-voltage transducer after application of the AC signal. The optical sensitivity of the spectrophotometer is detected by the voltage difference detector and the electrical gain is detected by the voltage variation rate detector.