GB870627A - Improvements in or relating to multi range testing devices - Google Patents

Abstract

870,627. Electric measuring instruments; range-changing circuits. BUSH & RANK CINTEL Ltd. July 31, 1958 [Aug. 1, 1957], No. 24396/57. Class 37. Testing apparatus has a test circuit terminating in probe members which are applied to a circuit or component under test, and which carry or include a manually-operable switch or switches arranged to vary the test range of the test circuit. One probe comprises an insulating sheath 1, Fig. 1, with a contact 2 connecting a circuit or component under test to a test circuit through wire 7, and a button 8 which when depressed closes spring contact 5 onto contact 6. The range of an ohmeter is altered by switches 30, 31, Fig. 3, of probes 20, 21, actuating one or both of relays 28, 29 whose contacts 28a, 29a select either one or two of the known resistances of network 22-25. The probes are applied across the unknown resistance, and the voltage drop across the system, which is supplied by a battery 33, is applied to a voltage sensing device at terminals 26, 27. The lowest resistance of network 22-25 may comprise the coil of a relay which operates a buzzer when the probes are short-circuited. Relays 28, 29 may also operate devices such as lamps, to indicate which range is in use. A probe may carry a number of switches, and these may comprise an insulating ring outside sheath 1 and having cam faces on its inner surface.