GB874923A - Conductivity cell - Google Patents

Abstract

874,923. Detecting impurities in fluids. McNAB Inc. Sept. 8, 1959, No. 30658/59. Class 37. An electrode structure for a conductivity cell comprises three coaxial disc electrodes 9, 19, 29, the outer electrodes 9, 29 being connected electrically to the support 1 for the structure and the central electrode 19 being insulated therefrom by a sleeve 21 of insulating material. The faces of the electrodes are coated with platinum and the central electrode 29 may be made of titanium. The lead 39 for the electrode 19 passes through a liquidtight seal provided by a grommet 43 compressed between a washer 41 and a retaining screw 45. The lead is secured to the electrode by means of a set-screw 51. The portion of the support 1 on the side of the seal remote from the electrodes serves as a housing for a temperature compensating thermistor 33. Heat transfer between the thermistor and the body of the structure is provided by a silicone oil bath 35 surrounding the thermistor. In use the electrodes project through a fitting into a liquidflow conduit, for example on a ship to detect the salt concentration in the water flowing therethrough. In a modification, Fig. 4 (not shown), the outer electrodes are formed integrally with the support member, instead of being secured thereto by the bolt 15, and the central electrode is made in two parts so that it can be fitted around the stem joining the outer electrodes. The support houses a temperature-compensating thermistor which, however, in this embodiment is encased in an epoxy-resin block having good heat-conducting properties. To prevent conduction between the central electrode and the conduit, the cylindrical peripheral surface of the central electrode may be given an insulating coating as may also the inner surface of the conduit where it is adjacent the electrodes.