H - Electricity – 02 – H
Patent
H - Electricity
02
H
348/39
H02H 3/26 (2006.01) H01H 47/00 (2006.01) H01H 9/16 (2006.01)
Patent
CA 1306047
53,663 ABSTRACT OF THE DISCLOSURE Long conductors which interconnect control pushbuttons such as STOP, START and RESET pushbuttons to the basic control circuit for an electromagnetic contactor or controller often have distributed capacitance between parallel lines in a common cable. This distributed capaci- tance may conduct capacitive current from the power supply line to a parallel control line the control pushbutton of which is in the off state. However, this latter current interacts with high impedance in the control circuit for producing a voltage which may be of a magnitude which would otherwise be supplied by an ON pushbutton. A microproces- sor periodically samples the voltages and may mistake the False signal due to the capacitive current for a true signal which would be caused by an ON pushbutton. In order to discriminate between a TRUE signal and a False signal the first capacitor is connected between the power supply conductor in system common and a second capacitor is connected between a signal conductor and system common. The capacitance value of the first capacitor is deliberate ly made smaller than the capacitive value of the second capacitor so that under normal circumstances the alternat- ing voltage on the second conductor logs the alternating voltage on the first conductor by an amount ? except when the voltage on the second conductor is provided by the aforementioned distributed capacitive leakage current between long lines in which case the voltage on the second conductor will lead the voltage on the first conductor by 66 53,663 an amount ? due to the capacitive nature of the current which causes it. The microprocessor therefore is condi- tioned to look at the two voltages immediately after the voltage on the first conductor changes state. If at that time the voltage on the second conductor is of the same digital plurality as the voltage on the first conductor then the signal on the second conductor is a true signal indicative of a closed pushbutton. If however it is not then the signal on the second conductor is a false signal indicative of the flow of capacitive current between lines rather than a closed pushbutton.
558307
Riches Mckenzie & Herbert Llp
Westinghouse Electric Corporation
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