IE41733L - Conductivity monitoring system - Google Patents

Abstract

1501890 Conductivity monitoring and measurement BAXTER TRAVENOL LABORATORIES Inc 23 Oct 1975 [31 Oct 1974 5 Feb 1975 (2)] 43684/75 Heading G1N The conductivity of a flowing liquid is measured in a housing 10 containing a common electrode 21 and first and second electrodes 20, 22 unequally spaced from the common electrodes. Substantially equal currents are driven between the common electrode and the first and second electrodes respectively and the difference in voltage drop, which is a measure of the liquid conductivity is fed to an indicator. Temperature compensation is provided by thermistor 32 and means are provided to operate the indicator if the thermistor fails. Oscillator 42 (500Hz) is coupled via transformer 72 directly to common electrode 21 and via equal resistors 51, 52 (constant current supply) to electrodes 20 and 22. The difference voltage is extracted by transformer T 1 and fed via amplifier 55 to summing amplifier 58. The output of thermistor 32 is also fed to amplifier 58 after amplification at 59. The temperature compensated conductivity signal from amplifier 58 is fed to sample and hold circuit 82 controlled by oscillator 42 and the resulting D.C. signal is smoothed at 67 and fed to indicator 69 and high and low threshold circuits 75, 76 supplying warning signals via gates 70, 71. If thermistor 32 becomes defective, the high resulting voltage from amplifier 59 is sensed by amplifier 97 which drives the output circuit to the out of range alarm condition. [GB1501890A]