One out of N code relay test circuit - uses test contact chain to switch error indicating relay if more than one main relay is switched

摘要

A number of relays in a telephone system operate on a 1 out of 'n' code. A set of contacts are coupled in a chain such that an error is indicated if more than one relay is energised at a given time. The relays (R1 to Rn) have contacts (r11-Rn1) coupled in a chain, with the common contacts commoned over diodes (G2, Gn) to the coils of an error indicating relay (AW). The switched contacts are connected over individual resistors (W1 to Wn) to a test voltage signal source. When the test voltage is applied (-U) the error indicating relay is only energised if there is more than one code relay switched.