| 摘要 |
It is common for lamps to be controlled from two switches so that, for example, a hall light can be turned on and off by either of two switches. There are occasions when it would be desirable for the lamp to be controlled by more switches, for example a switch at both ends of the hall and another on the landing above. <??>An electrical switch for AC is disclosed, for connection in parallel with others of the same kind. The switch has an operating member, a controlled switching device and a controller for controlling the time in a cycle from which the switching device conducts. The controller is responsive to the voltage across the switching device to detect a time in a cycle from which the switching device in one of the parallel switches conducts so as to determine whether all parallel switches are idle, that another switch is on, or when it is itself on that another switch has been operated. <??>When all parallel switches are idle the controller is responsive to an operating signal produced by operation of the operating member to perform an on function causing the switching device to conduct from a first set time within the cycle. The controller is being responsive to a subsequent operating signal to cause the switching device not to conduct, or to the determination that another switch has been operated to cause the switching device not to conduct. When another parallel switch is on, the controller is responsive to the operating signal to cause the switching device to conduct from a second set time in advance of the first and to perform an off function. <??>Installation of the switches is simple since they need only to be connected in parallel at the switch or the light fitting. Each switch can then both turn on the light or turn it off independently. <IMAGE>
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