4-20 mA interface circuit

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

2007-05-01

2007-05-01

Nguyen, Matthew V. (Department: 2838)

Electricity: power supply or regulation systems

In shunt with source or load

Using impedance

Reexamination Certificate

active

10496677

ABSTRACT:
A 4–20 mA interface circuit is disclosed having a resistor in series with a DC/DC converter, and further having a current bypass circuit in parallel to the series combination of the resistor and DC/DC converter. In this way, a 4–20 mA analog current at a low frequency may be bypassed around the series combination, whereas a high-frequency current carrying a digital communications signal may be presented with the resistor as its only effective input impedance. In this way, the 4–20 mA current sees an input impedance which allows the 4–20 mA current to be used in supplying power to an external device, whereas the high-frequency current sees an impedance which allows a reliable, low-distortion reading of the digital communications signal therefrom. The high-frequency current may be superimposed on the 4–20 mA, low-frequency current. Portions of the 4–20 mA current not required to power the external device may be shunted to ground, or may be driven back through the DC/DC converter, to thereby present a negative impedance to the 4–20 mA current.

REFERENCES:
patent: 5001358 (1991-03-01), Matsuoka et al.
patent: 5159543 (1992-10-01), Yamawaki
patent: 6140807 (2000-10-01), Vannatta et al.
patent: 6600297 (2003-07-01), Takeda et al.
patent: 6657405 (2003-12-01), Yang
patent: 6900696 (2005-05-01), Lautzenhiser et al.

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