Process control instrument with loop overcurrent circuit

Details Process control instrument with loop overcurrent circuit Process control instrument with loop overcurrent circuit

1990-07-26

1993-01-12

DeBoer, Todd E.

Electricity: electrical systems and devices

Safety and protection of systems and devices

Voltage regulator protective circuits

361 58, 361 82, 361 84, H02H 308

Patent

active

051794888

ABSTRACT:
A process control instrument receives a DC current from a two wire loop and has overcurrent protection and reverse current protection circuits which pass a portion of the DC current as a device current to a process controlling device. The overcurrent protection circuit includes a current sensing circuit which conducts the device current and generates an output indicative of device current. The overcurrent protection circuit also includes a current diverting circuit coupled across the two wire loop and responsive to the sensor output for diverting loop current in excess of a predetermined upper limit of device current back to the loop when the sensor output indicates the upper limit is reached. The reverse current protection circuit is coupled across the loop and includes a variable impedance which conducts the device current. The variable impedance inhibits the device current from flowing through the device when a loop potential is reversed from a predetermined polarity. Thus, the device current is limited to a current range controlled by the variable impedance and the upper limit.

REFERENCES:
patent: 3582713 (1971-06-01), Till
patent: 3975719 (1976-08-01), Frick
patent: 3992650 (1976-11-01), Iwasa
patent: 4481967 (1984-11-01), Frick
patent: 4533970 (1985-08-01), Brown
patent: 4665938 (1987-05-01), Brown
patent: 4678984 (1987-07-01), Henze
patent: 4783659 (1988-11-01), Frick
patent: 4857985 (1989-08-01), Miller

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