Q. Draw a 100 line exchange using two motion selectors and elucidate, how switching takes place in it.

Ans:

In a 100 line exchange, every subscriber is assigned a 2 digit telephone number between 00 and 99. This number identifies group selector value and final selector values. As the dialing of telephone number is done the corresponding group selector and then final selector levels are switched. Desired schematic for 100 lines exchange with 24 two motion selectors is shown in Figure.

In this case, 24 simultaneous calls can be put through switch. Generally a 24-outlet Uni-selector is used as a selector hunter. Every one of the 24 outlets is connected to one two-motion selector. So a subscriber has access to all the 24 two-motion selectors in system. Corresponding outlets of all the selector hunters are commoned and hence all subscribers have access to all the two-motion selectors. This scheme is displayed in Figure. Call establishment in this scheme takes place in two steps. Firstly, when subscriber lifts his receiver handset, his Uni-selector hunts through contact positions and seizes a free two-motion selector. At the subsequent step, two-motion selector responds to dial pulses for appropriate connection.