sentences:  In the event of the equipment detecting a serious fault in one of the side-conscious units, all the units in that section were locked onto the side which was giving good service and a prompt alarm was sent to a manned centre to indicate that the exchange needed urgent attention.In normal service, the exchange automatically changed all three sections from one side to the other every eight minutes.If Call Control detected eight failures to set up calls within that eight minutes, then it force-changed all the side-conscious units onto the other side, locked that side in service and raised a prompt alarm.