GB680601A - Improvements in or relating to time delay control of electrical apparatus - Google Patents

Abstract

680,601. Controllers; switches held set and freed mechanically. TIPPING, F. C. May 7, 1951 [Feb. 10, 1951], No. 3300/51. Classes 38 (iii) and 38 (v) Relates to means, -for automatically switching off the electric driving motor of a machine at the end of a predetermined period after the machine has ceased to be driven. When the machine is in motion a striker arm 15 is oscillated by a driven part of the machine such as a centrifugally operated cam. This causes a spring-loaded push-rod 14 to be raised and a pivoted lever 13 reciprocated so that a spring-loaded piston 12 and parallel-connected mercury switches 32 are moved to and retained in their uppermost positions. The piston movement causes the inner cylinder of a dashpot 11 to fill with oil. When the apparatus is in the normal position shown, one mercury switch is open and the other closed. During the upward movement, the normally open switch closes and subsequently the normally closed switch opens so maintaining the closure of a push-button operated contactor through which the motor is energised. When the machine is declutched the striker arm 15 ceases to move and returns to the equilibrium position shown. The piston 12 slowly descends at a rate determined by the setting of screw 22 of a throttle valve. During the descent both mercury switches open to disconnect the motor, the switches finally returning to their normal position. The dashpot comprises a double-walled cylinder, the space between the walls acting as an oil reservoir, the inner wall having a one-way valve 21, in addition to the throttle valve, for allowing oil to pass to the inner cylinder. The upper part of the inner cylinder wall is perforated so that, when the piston is raised, the passage of oil through the valve is enhanced by the air behind the piston passing into the space between the walls under pressure. A screw 37 adjusts the angular separation of the mercury switches.