Patent GB-677599-A (GB)
Title: Electrical process and apparatus for detecting changes in composition of a liquor
IPC: G01N27/04
Filed: 1951-01-05
Abstract: 677,599. Measuring constituents of liquids. WALLACE & TIERNAN PRODUCTS, Inc. Jan. 5, 1951 [Jan. 7, 1950], No. 449/51. Class 37. Apparatus for detecting departure of the chemical composition of a liquid from a predetermined limit by detecting changes in its conductivity comprises a conductivity cell in series with the secondary of a transformer, means for supplying current to the primary of the transformer, and means for detecting departure from a predetermined limiting value of the impedance of the primary of the transformer in response to changes in the conductivity of the liquid. The chlorine concentration limit indicator shown is applied to a chlorine injection system of the type described in Specification 643,865. Aqueous liquid to be chlorinated passes through a main 10 having a branch pipe 12 conveying a stream of water to which chlorine is supplied from a chlorinator 14. The concentration of chlorine in the liquid passing through the pipe 12 is measured in a cell 20 having electrodes 26 which are connected to the secondary winding 32 of a transformer 34. The high impedance primary winding 36 is connected in series with a potentiometer 38 across the secondary winding 40 of an isolation transformer 42 the primary winding of which is connected through a switch 48 to an A.C. supply 46. Connected in parallel with the primary 36 and potentiometer 38, and across the secondary 40 of the transformer 42 is a cold cathode gas-filled valve 50 having an anode 52 and a cathode 54. In the anode circuit is a relay energizing coil 58 shunted by a half-wave selenium rectifier 60 arranged to conduct current only in the direction in which the valve 50 is non-conducting. Through a small condenser 61 the grid 62 is connected to the slider of the potentiometer 38, the cathode 54 being connected to the common side of the potentiometer 38 and the secondary 40. A high resistance 63 is connected between the grid 62 and cathode 54. The valve 50 is biased so as to become non-conducting when the chlorine concentration is less than a predetermined minimum and to be conducting when the concentration is at or in excess of that minimum. The valve 50 conducts during positive half-cycles and is non-conducting during negative half-cycles, so that a pulsating current flows through the coil 58. The rectifier 60 provides a path through which the E.M.F. developed by the collapsing magnetic field of the relay can discharge during each negative half-cycle, so that the relay is substantially continuously energized and the normally closed contacts 64 are opened when the conductivity of the liquid in the cell 20 is within the predetermined limits. The contacts 64 close to actuate an alarm 66 if the chlorine concentration falls below the predetermined low limit or if the device becomes inoperative due to valve failure. An additional secondary 68 in series with an indicator light 70 is provided to show when the power is on. In a modification the rectifier 60 is replaced by a condenser and a resistance is included in series with the anode 52. The winding 58 forms one winding of an alarm buzzer, which also has a second winding connected in series with a resistance and rectifier across the secondary winding 40.