ELECTROMAGNETIC CONTACTOR WITH UNIVERSAL CONTROL

摘要

An electrical motor contactor or controller is taught in which control signals from remotely located pushbuttons are supplied to the logic portion of the controller for the purpose of initiating or stopping a predetermined contactor or controller actions. The controller or contactor is of a universal nature adapted for the acceptance of relatively high voltage AC control signals or relatively low voltage DC control levels. For instance, a 120-volt AC signal may be provided or a 5-volt DC level may be provided. Because an AC signal may be provided to the controller, capacitive filter elements are utilized in the control circuit for filtering transients or AC components above a predetermined frequency which may be 60 Hz for example. Furthermore, voltage regulator elements within the control circuit and the microprocessor input terminals within the control circuit represent relatively high impedance in the discharge path for the aforementioned capacitors. Furthermore, regardless of whether DC control signals or AC control signals are supplied to the control circuit, all values are converted to relatively low level DC values for utilization as inputs by the microprocessor. In those circumstances in which an AC control signal is utilized interruption of the AC control signal, such as may occur when a closed pushbutton is opened, alerts the microprocessor that a change in control state has taken place. The capacitive elements which are used as filters may retain a charge thereacross for a significant portion of time because of the presence of the high impedance discharge paths. Therefore, the microprocessor in reading the control line may mistake the residual voltage on the charged capacitor for a positive indication of a control signal. In order to avoid this, it is necessary to periodically in a controlled manner attempt to discharge the capacitive elements so that subsequent readings will not give a false indication. In order to do this, the input terminals of the microprocessor are periodically provided with digital logical zero value which represents a near short circuit condition for the capacitors thus, discharging the capacitive elements.