GB943912A - Improvements in or relating to electric limit switches - Google Patents

Abstract

943,912. Control of several motors; retractive switches. JOHN THOMPSON COMPOST PLANT Ltd. June 16, 1960 [April 16, 1959], No. 13013/59. Headings H2B and H2J. A switch unit comprises mercury switches 1 and 2 carried on an arm 3 pivoted at 4 in a casing 5, the arm 3 being biased by a spring 6 and being in the path of a rotating striker pin 7. Switch 1 is a changeover switch having two pairs of contacts A, B and switch 2 is an on/off switch having a single pair of contacts C, the switch 2 being secured at a more actute angle to the arm 3 than the switch 1. The unit is used in a motor control circuit, e.g. for an installation including rotary hoppers on different floors of the same building comprising a first motor M1 which actuates the pin 7 and a second motor M2, the arrangement being such that switch 2 prepares motor M2 for operation by switch 1 automatically on completion of one revolution of the motor M1. In operation, with motor M1 stopped contacts A and C are open and contacts B are closed (Fig. 3, not shown), M1 is started by closing contacts D; M2 cannot then start because of open contacts E in series therewith. As motor M1 rotates, first contact A and then contacts A and C together (Fig. 4, not shown, and Fig. 1) are made, the contact A completing the holding- on circuit of M1 and contact C energizing a slow-release relay R which closes contacts E to prepare a circuit to start motor M2. As motor M1 comes to the end of its first revolution contact C is open (Fig. 2, not shown); the switch unit then assumes the starting condition (Fig. 3, not shown), with contacts A and C open, and motor M2 starts up, contacts B being then closed; the slow-release characteristic of relay R holds the contacts E closed sufficiently long to allow the second motor to be started and its running circuit to be completed over its own holding contacts (not shown).