GB960666A - Electrically operated liquid level detector - Google Patents

Abstract

960, 666. Automatic liquid level control. CANDY FILTER CO. Ltd. March 22, 1963 [April 6, 1962], No. 13395/62. Heading G3R. In a system in which an electrically operable control relay is connected to electrode means in a conducting liquid so that the relay is energized when the liquid is at one level and de-energized when the liquid is at another level, the relay armature, if it is in the "energized" position between levels, is maintained in that position if the electric supply is interrupted, even momentarily. With the circuit as shown, rise in the level of an electrically conducting liquid in a drain pit 2 can occur until a circuit is completed between electrodes 8, 11 so that winding 13 of a relay 1 is energized from a mains source 4 through a step-down transformer 3 and a rectifier 5. Armature 17 of relay 1 is then attracted to start a pump to empty the pit. Contacts 18 of relay 1 also close to connect a further electrode 21 to electrode 11 so that relay energization is maintained until the liquid level is reduced below electrode 21. The core of relay 1 has sufficient residual magnetism so that, if the mains supply fails, the pump does not cease operating. Contacts 15 are also closed when relay 1 is operated and the consequent energization of opposing relay winding 14, though insufficient to cancel the effect of winding 13, ensures the release of relay 1 when the liquid level falls below electrode 21. Connection to an electrically conducting container instead of electrode 8 and operating an alarm instead of a pump, are referred to.