Type-7 crossbar selector

THE TYPE-7 crossbar selector is a mechanism for selecting one of several trunk groups in a dial telephone switching system. Each of these trunk groups may lead to a subsequent rank of group selectors, to connectors (final selectors), to outgoing trunks, or to one of several special services. Switching in this case is based on a system of decimal numbering; consequently the selector, in response to a single pull or digit of a telephone dial-calling device, provides a choice of one trunk group out of 10. The selector consists of a group of relays, a magnetic impulse counter to register the digit, and certain permanently associated portions of several crossbar switches. Generally, each selector has access to 100 outlets, which are arranged in 10 groups of 10 paths each.