Westinghouse Electric Corporation

John G Leddy

Joseph C Engel

Gary F Saletta

A motor controller system is taught in which an overload relay board utilizes a current monitor which produces an output signal which is related to the current being sensed thereby over a wide range of currents which may vary for instance between 1 and 1,000 amperes. This indicative signal is converted to a DC voltage level which is then provided to the analog-to-digital portion of a microprocessor for being converted to a digital number for being processed by the microprocessor for causing the contacts of the motor controller to open at appropriate current values. The system utilizes an integrating capacitor which samples the output current from the sensor 32 times in succession providing a voltage which is proportional to the line current. This voltage which may exceed the input voltage level of the analog-to-digital converter is nevertheless supplied to the analog-to-digital converter and sampled internally by the microprocessor at double the line cycle time period until the 32 samplings have expired. If at any time during this doubled sampling process the output of the analog-to-digital converter digitally saturates, the left shifting technique is provided with other memory locations within the microprocessor to provide an approximate double value of voltage so that at the end of the 32 line half cycles a very close approximation of the actual current is contained within storage locations within the microprocessor for effective utilization thereby.

Electromagnetic contactor with wide range overload current relay board

An electromagnetic contactor is taught which includes a conduction angle controlled triac or similar gated device which is connected in series circuit relationship with the winding of an electromagnetic solenoid or coil which is responsible for closing the contactor contacts and for keeping them closed. The current flowing through the triac is fed to a microprocessor which digitizes the current and compares it to a stored standard. The conduction angle is then decremented or incremented as necessary to change the conduction angle to cause less or more current to flow per half cycle until the amount of current flowing as sensed on a half-cycle-by-half-cycle basis is equal to the current represented by the stored standard.

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Brookline, MA, United States of America

John G Leddy