| A
wide range of electromechanical relays was employed in crossbar
offices. Most of the control relays in crossbar offices built in
the 1940's and 1950's were of the 'U-Y' type, also known as
flat-spring.
In the 1960's
the wire-spring relay, with faster actuation and improved
contact life was introduced.
Large versions
('multi-contact') of both flat- and wire-spring relays were used
to momentarily connect the markers with other equipment in the
office.
Reed relays
were used for digit storage and assembled into packages of five
relays each. One of these can store a single digit. They used a
2-out-of-5 code: 0,1,2,4,7. The digit '0' is stored as
4+7.
All
transmission paths were switched on crossbar switches, which
generally came in 200-point or 100-point varieties, and in
3-wire or 6-wire versions. These formed the switching fabric of
the network. |
BACK
TO CROSSBAR MAIN PAGE
