Apparatus for detecting and controlling the presence of sewage and other sludges in a liquid

Claim 1

APPARATUS FOR DETERMINING THE SLUDGE DENSITY OF A LIQUID COMPRISING AN ELECTRIC CONDUCTIVITY PROBE HAVING TWO SPACED ELECTRODES FOR INSERTION IN THE LIQUID, A TRANSFORMER HAVING A PRIMARY AND A SECONDARY WINDING, A FIRST SOURCE OF ALTERNATING CURRENT TO ENERGIZE SAID PROBE, VOLTAGE SELECTING MEANS FOR SETTING A DESIRED SLUDGE DATUM LEVEL CONNECTED TO SAID PRIMARY WINDING PROBE AND FIRST SOURCE, WHEREBY THE ALTERNATING CURRENT FLOWING THROUGH SAID PROBE VARIES WITH THE RESISTANCE OF SAID LIQUID BETWEEN SAID ELECTRODES IN DEPENDENCE UPON THE SLUDGE DENSITY THEREOF AND A SELECTED PROPORTION OF THE VOLTAGE DROP IN SAID VOLTAGE SELECTING MEANS DUE TO SAID CURRENT IS APPLIED TO SAID PRIMARY WINDING, A SECOND SOURCE OF ALTERNATING CURRENT, SECOND VOLTAGE SELECTING MEANS CONNECTED TO SAID SECOND SOURCE AND SAID SECONDARY WINDING, A THREE-ELECTRODE ELECTRON TUBE HAVING A CONTROL ELECTRODE AND TWO OTHER ELECTRODES FOR CONNECTION IN A POWER CIRCUIT, SAID CONTROL ELECTRODE BEING CONNECTED TO SAID SECONDARY WINDING SO THAT AN ALTERNATING VOLTAGE BIAS SELECTED BY THE SETTING OF SAID SECOND VOLTAGE SELECTING MEANS IS APPLIED TO SAID CONTROL ELECTRODE TO MAINTAIN