Input channel diagnostics
First Claim
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1. A method of internally testing an input channel for a safety critical system, the method comprising:
- adding a subliminal perturbation signal to an input signal to be applied to an input circuit;
detecting an output signal from the input circuit; and
assessing operability of the input channel by determining whether addition of said subliminal perturbation signal causes a change in said output signal.
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Abstract
This invention relates to input channel diagnostics for an industrial process control system. The invention provides improved apparatus and methods relating to fault containment, overload protection and input channel diagnostics.
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Citations
11 Claims
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1. A method of internally testing an input channel for a safety critical system, the method comprising:
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adding a subliminal perturbation signal to an input signal to be applied to an input circuit; detecting an output signal from the input circuit; and assessing operability of the input channel by determining whether addition of said subliminal perturbation signal causes a change in said output signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of internally testing an input channel for a safety critical system, the method comprising:
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adding a perturbation signal to an input signal to be applied to an input circuit; detecting an output signal from the input circuit; determining whether addition of said perturbation signal causes a change in said output signal; passing the input signal from an input circuit that includes one or more series resistors that have a total resistance that is at least two orders of magnitude greater than the resistance of a conditioned sensor signal source; and passing the input signal through a fuse that is oriented in series with the one or more series resistors and has an operating threshold that is lower than an operating threshold of the one or more series resistors. - View Dependent Claims (11)
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Specification