Microprocessor based electrical apparatrus with false AC input rejection
AssigneeEaton Corporation
InventorRobert T. Elms
Life of this patent
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Abstract
False ac signals produced by a noise suppression capacitor across a switch applying a switched ac line voltage signal to a logic input of a microprocessor in an electrical apparatus such as, for example, a contactor or circuit breaker, are phase shifted with respect to a true ac input by inserting two series resistors, and a diode shunting one resistor, between the switch and the logic input. This creates a larger window in which to discriminate between the zero crossings of the true and false ac signals.
Claims12
An electrical apparatus for controlling an electrical load in response to an ac voltage signal switched by a switch shunted by a noise suppression capacitor which produces, when said switch is open, a false signal leading by a predetermined interval a true ac switched signal produced when said switch is closed, said apparatus comprising:
- a microprocessor having an input filter and an input terminal to which said ac voltage switched by said switch is applied, and means periodically reading said ac voltage switched by said switch applied to said input terminal;
- and
- discriminating means connected between said switch and said input terminal increasing said interval by which said false signal leads said true ac switched signal, said means periodically reading said ac voltage reading ac voltage applied to said input terminal during said interval.
Dependencies are inferred from the claim text.