GB834098A - Improvements in or relating to devices for preventing the unauthorised use of low-current apparatus - Google Patents

Abstract

834,098. Switches held set and freed mechanically. ZOGMAL, R. P. Oct. 21, 1957 [Oct. 4, 1957], No. 32774/57. Class 38 (5). In a switch for preventing unauthorized use of apparatus, contacts 9, 10 on blades 7, 8, respectively, are kept open by an insulating pin 20 on blade 7 bearing against part 18a of a key-operated lockbolt 18. The latter is held in the position shown, against a spring 22, by the arm 16a of a lever 16 pivoted at 15, the pivot 15 and contact-carrying block 11 being mounted on a U-shaped bracket 13. To prevent unauthorized use, the end 16b of lever 16 is depressed by a button 21, which releases lockbolt 18 and allows the contacts to close, the switch being reset by a key fitted into lock 19. Preferably, button 21 must be pressed to below the surrounding lip 23 so as to guard against accidental tripping of lever 16 by a heavy falling object. An emergency unlocking device comprises a rod 24 which is normally held in a retracted position by a wire and lead seal 26, breakage of the seal allowing a spring 25 to advance the rod 24 to the open-contact position shown. Closure of the contacts may serve to short-circuit pulse initiating contacts of telephone apparatus to prevent outgoing calls.