Telephone exchange connections failure alarm - indicates failure of given number of connections between telephone exchanges and avoids effects of ref. volts of variation

摘要

The alarm system, for indicating the failure of a given number of communications connections between telephone exchanges etc., avoids the effects of variations in the internal resistance of the reference voltage source used for the comparative detection of line failure (as described in the main patent). A fixed reference voltage divider (R1, R2) is provided for the given reference voltage and has division ratio of 1/2. This divider is coupled to the diff. amplifier. A variable divider is coupled to the second input of the amplifier and has alarm contacts (K) switching in various weighting resistors (R) in addition to the selected resistors.