4-20 mA interface circuit

Details 4-20 mA interface circuit 4-20 mA interface circuit

2005-06-14

2005-06-14

Ha, Dac V. (Department: 2634)

Pulse or digital communications

Cable systems and components

C375S377000, C251S129010, C700S289000

Reexamination Certificate

active

06907082

ABSTRACT:
A 4-20 mA interface circuit for use, for example, in a valve controller, communicates with a two-wire loop. The interface circuit includes a power extraction circuit connected to the two-wire loop and operable to generate a DC operating voltage for use in powering the interface circuit and a related device, the power extraction circuit including a DC-to-DC converter that generates the DC operating voltage as a voltage having a smaller magnitude than a voltage between the two wires of the two-wire loop. The circuit also includes a current sensor connected to the two-wire loop and operable to generate a measure of an analog current through the two-wire loop, the measure being used in controlling a device associated with the interface circuit, and a digital communications circuit connected to the two-wire loop. The digital communications circuit is operable to inject a digital transmission signal on to the two-wire loop and to extract a digital reception signal from the two-wire loop. The digital communications circuit includes an impedance controller having an operational amplifier connected to control an impedance presented to the two-wire loop by the interface circuit.

REFERENCES:
patent: 5502999 (1996-04-01), Seberger et al.
patent: 5533544 (1996-07-01), Good et al.
patent: 5804696 (1998-09-01), Seberger et al.
patent: 6026352 (2000-02-01), Burns et al.

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