Analytical redundancy using band-limiting filters

A method is described whereby faults in control systems may be detected on the basis of the generation and crosscomparison of bandlimited signals from dissimilar sources. While signals measured at different points in the system may differ widely when viewed over a wide bandwidth, over limited pass bands there are shown to exist simple relationships which can be verified by means of appropriate filtering and comparison logic. The band-limiting filters employed are, in effect, used to monitor the propagation of information, originating in the structure of external inputs, through the system.