PH METER WITH SELF-DIAGNOSING FUNCTION

摘要

PURPOSE:To automate the judgement on the deterioration of a glass electrode with high accuracy and to enable alarming at an optional deterioration level by providing a function to add a means for detecting automatically film resistance within a converter circuit. CONSTITUTION:Inter-electrode liquid resistance clamps the potential of an electrode terminal RE to the reference potential COM of the circuit and acts as input resistance to receive the AC signal of an amplitude Vk from an AC generating circuit 3 via a capacitor C1. The AC component V0 in the output voltage is cut off of the DC component of a capacitor C3 and is then converted to a DC voltage V1 by a rectifying and smoothing circuit 5. On the other hand, a smoothing circuit 6 smooths the AC component V0 and takes out a DC component V0. The output passes through a temp. compensating circuit 7 which receives a measured liquid temp. signal Vt and calculates the pH value converted to a reference temp. and supplies a pH measuring output V2 to an output terminal 8. A temp. compensating circuit which receives the DC voltage V1 associated to film resistance Rg and the signal Vt and makes calculation is provided in addition to the above-mentioned circuit. An alarm circuit 12 which receives an alarm set voltage Vs and applies an alarm signal to a terminal 13 when V1<=Vs is also provided.