GB1305317A - - Google Patents

Abstract

1305317 Thermal switches; electromagnetic switches; continuous interrupters WAGNER ELECTRIC CORP 19 April 1971 [24 Feb 1970] 22309/71 Heading H1N Three electrically operated switches 12, 22, 40 are arranged and connected to form a flasher unit whose on-off periods are substantially independent of supply voltage or load current. The switch 12 is a series flasher unit comprising an expansible strip 17 heated by the load current flowing through it to operate a snap acting strip 14 and thus open contacts 18, 20. The switch 40 comprises a spring blade contact 46 operated by an electromagnet 42 in series with switch 12. Switch 22 comprises a spring blade contact 24 normally held open by an expansible wire 26 connected in series with a ballast resistor 38 across switch 12; the electromagnet 42 serves also to hold contacts 24, 32 of switch 22 closed until wire 26 is sufficiently cooled. When the external circuit is closed strip 17 is heated until contacts 18, 20 open; they remain open for a fixed time determined by the cooling of strip 17; this is the off-time of the flasher unit. While contacts 18, 20 are open wire 26 is heated and contacts 32, 34 are closed by it. When the contacts 18, 20 reclose the magnet 42 closes contacts 48, 50 completing a shunt circuit around switch 12 so that strip 17 is not heated. After a time, dependent on the energy supplied to it while contacts 18, 20 were open, the wire 26 opens contacts 32, 34 to break the shunt circuit. Strip 17 then heats up to open contacts 18, 20 again. The on-time of the flasher unit is thus the sum of the cooling time of wire 26, which increases with increasing load current, and the heating time of strip 17, which decreases; the total on-time is thus substantially constant.