Selection control for private exchange - prevents unauthorised extensions making long:distance calls by means of contact breaking circuit controlled by decade counter

摘要

The selection control, for a private branch exchange, allows distinctions to be made between those extensions authorised to make long-distance calls and those not. Metering pulses are produced by breaking the connection. The circuitry that controls the break contacts (Tr) is connected to a decade counter (DZ). A signal operating the break contacts is only effective for a given counter setting (eg step 3). The decade counter has an anti-chatter circuit (EP) connected on its input side to prevent the contacts (Zr) producing the counter's count-on pulses from chattering.