True hysteresis window comparator for use in monitoring changes

Details True hysteresis window comparator for use in monitoring changes True hysteresis window comparator for use in monitoring changes

1994-12-14

1996-01-30

Callahan, Timothy P.

Miscellaneous active electrical nonlinear devices, circuits, and

Specific signal discriminating without subsequent control

By amplitude

327 77, 324500, H03K 5153

Patent

active

054883237

ABSTRACT:
Electronic circuitry is disclosed for interfacing with a plurality of two-position switches to determine if each switch is opened, closed or faulty to some extent. Each switch is connectable in series with a pull-up resistor and between two different voltage values. The switch provides an output voltage at the connection of one terminal of the switch with the pull-up resistor. This switch voltage is presented to both an inverting input of a first comparator and a non-inverting input of a second comparator. The non-inverting input of the first comparator has a reference voltage of a certain value applied thereto, while the inverting input of the second comparator has a reference voltage of a certain value also applied thereto, the reference voltage values being different so as to define a "window" or "dead band" region of voltage. The switch output voltage is compared to the reference voltages on the two comparators. If the switch is closed, the comparator outputs will assume certain states. On the other hand, if the switch is opened, the comparator outputs will assume the opposite states. Finally, if the switch is faulty such that a finite impedance value is developed across the terminals of the switch, the voltage value will then be generated which causes both comparator outputs to assume the same state, thereby indicating a faulty switch to subsequent signal processing circuitry.

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