Photometering apparatus

Abstract

A turbidimeter for measuring a turbidity of a test liquid including a hollow main body having openings formed at its lower end through which the test liquid is introduced into a measuring optical path within the main body, a semiconductor laser diode arranged in the main body at its upper end and emitting a laser light, a first prism arranged within the main body and guiding the laser light into the measuring optical path, a second prism arranged within the main body and guiding light emanating from the measuring optical path to the upper end of the main body, first and second semiconductor photodiodes arranged within the main body at its upper end such that the light emanating from the second prism is exclusively made incident upon the first semiconductor photodiode, and first and second operational amplifiers arranged within the main body at its upper end and amplifying output signals supplied from the first and second semiconductor photodiodes, respectively. Output signals generated from the first and second operational amplifiers are supplied to a differential amplifier to derive a difference therebetween, the difference corresponding to the turbidity of the test liquid. The differential amplifier is arranged remote from the main body, so that any error in the measured turbidity due to the temperature variation can be compensated for.