| 摘要 |
The invention is directed to a supervisory circuit for a control system of the type having a plurality of redundant input channels and a single output channel. More specifically, the invention is directed to a supervisory circuit for a two-channel redundant control system that provides reliability approaching that of a three-channel system. The supervisory circuit operates on the assumption that the majority of control circuit failures are catastrophic. The supervisory circuit includes a channel select circuit that receives the outputs of both of the identical control circuits and determines the faulted channel. Determination of the faulted channel is accomplished by a two-step comparison. In the first step, the outputs of both channels are compared with a previously stored output, or average of previous outputs. In the second step, signals representative of the absolute difference between each channel output and the stored output are compared. The polarity of the output of the second comparison determines the faulted channel. Normally, a manual channel select switch determines which channel is used as the output of the control system. In one embodiment of the invention an independent trip circuit determines when a fault has occurred in one of the two channels and disables the manual channel select switch in favor of the channel selection made by the channel select circuit. In another embodiment of the invention, the output of the channel select circuit is directly used to determine whether a fault has occurred and when the manual channel select switch should be disabled in favor of the channel select circuit.
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