Supply current regulator for two-wire sensors

• US 6,118,260 A
• Filed: 10/28/1999
• Issued: 09/12/2000
• Est. Priority Date: 10/28/1999
• Status: Expired due to Term

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Plagens, Mark Robert, Kirkpatrick, Richard Allen II
• Primary Examiner(s): NGUYEN, MATTHEW VAN
• Application Number:
  US09/429,445
• Time in Patent Office: 320 Days
• Field of Search: 323/269, 323/273, 323/277, 323/282, 323/312, 323/364, 323/367
• US Class Current: 323/312
• CPC Class Codes: G05F 1/565 sensing a condition of the system or its load in addition to means responsive to deviations in the output of the system, e.g. current, voltage, power factor G05F1/563 takes precedence
• CPC Class Codes: G08C 19/02 in which the signal transmitted is magnitude of current or voltage G08C19/36, G08C19/38 take precedence

Abstract

A current regulator is provided for a two wire sensor and comprises first and second conductors arranged to provide a sensor output current, a first resistance and a current reference coupled across the first and second conductors, and a second resistance and sensor load terminals coupled across the first and second conductors. An amplifier has first and second inputs and an output. The first input is coupled to a first junction between the first resistance and the current reference, the second input is coupled to a second junction between the second resistance and the sensor load terminals, and the output is connected to the second input. The amplifier controls a first voltage at the first junction to be substantially equal to a second voltage at the second junction.

Claims

1. A current regulator for a two wire sensor comprising:

first and second conductors arranged to provide a sensor output current;

a first resistance and a current reference coupled across the first and second conductors;

a second resistance and sensor load terminals coupled across the first and second conductors; and

,

an amplifier having first and second inputs and an output, wherein the first input is coupled to a first junction between the first resistance and the current reference, wherein the second input is coupled to a second junction between the second resistance and the sensor load terminals, wherein the output is connected so as to control the sensor output current in the first and second conductors, and wherein the amplifier is arranged so that a first voltage at the first junction is substantially equal to a second voltage at the second junction.

2. The current regulator of claim 1 wherein the output is coupled to the second input.

3. The current regulator of claim 1 wherein a sensor load is coupled to the sensor load terminals, and wherein the sensor load is coupled to the current reference so as to control the sensor output current.

4. The current regulator of claim 3 wherein the current reference includes a variable resistance coupled between the first junction and one of the first and second conductors, and wherein the variable resistance is coupled to the sensor load so as to control the sensor output current.

5. The current regulator of claim 4 wherein the output is coupled to the second input.

6. The current regulator of claim 4 wherein the sensor load includes a switch arranged to switch the variable resistance between only two discrete resistances.

7. The current regulator of claim 4 wherein the sensor load includes a switch arranged to switch the variable resistance between a plurality of discrete resistances.

8. The current regulator of claim 4 wherein the amplifier is an operational amplifier.

9. The current regulator of claim 1 wherein the amplifier is an operational amplifier.

10. The current regulator of claim 9 wherein the output is coupled to the second input.

11. A current regulator for a two wire sensor comprising:

first and second conductors arranged to provide a sensor output current;

a current reference coupled to the first and second conductors;

sensor load terminals coupled to the first and second conductors; and

,

an amplifier coupled between the current reference and the sensor load terminals in a closed loop feedback configuration so that the current reference is controlled so as to vary the sensor output current in relation to a sensed condition.

12. The current regulator of claim 11 wherein the amplifier has first and second inputs and an output, wherein the first input is coupled to the current reference, and wherein the output is coupled to the second input and to the sensor load terminals.

13. The current regulator of claim 12 wherein the amplifier is an operational amplifier.

14. The current regulator of claim 11 wherein a sensor load is coupled to the sensor load terminals, and wherein the sensor load is coupled to the current reference so as to control the sensor output current.

15. The current regulator of claim 14 wherein the current reference includes a variable resistance, and wherein the variable resistance is coupled to the sensor load so as to control the sensor output current.

16. The current regulator of claim 15 wherein the sensor load includes a switch arranged to switch the variable resistance between only two discrete resistances.

17. The current regulator of claim 15 wherein the sensor load includes a switch arranged to switch the variable resistance between a plurality of discrete resistances.

18. The current regulator of claim 15 wherein the amplifier is an operational amplifier.

19. The current regulator of claim 15 wherein the amplifier has first and second inputs and an output, wherein the first input is coupled to the current reference, and wherein the output is coupled to the second input and to the sensor load terminals.

20. The current regulator of claim 19 wherein the amplifier is an operational amplifier.

21. A current regulator for a two wire sensor comprising:

first and second conductors arranged to provide a sensor output current;

a current reference coupled to the first and second conductors, wherein the current reference comprises a plurality of components; and

,

a sensor load coupled to the first and second conductors and to the current reference, wherein the sensor load includes a voltage regulator, wherein the sensor load is arranged to control the current reference so as to control the sensor output current, wherein the current reference is coupled to the voltage regulator so as to render the current regulator substantially supply voltage insensitive, and wherein the components are selected so as to render the current regulator substantially temperature insensitive.

22. The current regulator of claim 21 wherein one of the components is a variable resistance, wherein the variable resistance is coupled to the sensor load, and wherein the sensor load varies the variable resistance so as to control the sensor output current.

23. The current regulator of claim 22 wherein the variable resistance varies with temperature in a first direction, and wherein another of the components varies with temperature in substantially the same direction.

24. The current regulator of claim 22 wherein another of the components is a voltage control device responsive to the voltage regulator so as to maintain the current regulator substantially insensitive to changes in supply voltage.

25. The current regulator of claim 24 wherein the variable resistance varies with temperature in a first direction, and wherein another of the components varies with temperature in substantially the same direction.

26. The current regulator of claim 22 wherein the sensor load includes a switch arranged to switch the variable resistance between only two discrete resistances.

27. The current regulator of claim 22 wherein the sensor load includes a switch arranged to switch the variable resistance between a plurality of discrete resistances.

28. The current regulator of claim 21 further comprising:

a first resistance arranged to couple the current reference across the first and second conductors;

a second resistance arranged to couple the sensor load across the first and second conductors; and

,

an amplifier having first and second inputs and an output, wherein the first input is coupled to a first junction between the first resistance and the current reference, wherein the second input is coupled to a second junction between the second resistance and the sensor load, and wherein the amplifier is arranged so that a first voltage at the first junction is substantially equal to a second voltage at the second junction.

29. The current regulator of claim 28 wherein the output is coupled to the second input.

30. The current regulator of claim 28 wherein the amplifier is an operational amplifier.

31. The current regulator of claim 28 wherein one of the components is a variable resistance coupled between the first junction and one of the first and second conductors, and wherein the variable resistance is coupled to the sensor load so as to control the sensor output current.

32. The current regulator of claim 31 wherein the variable resistance varies with temperature in a first direction, and wherein another of the components varies with temperature in substantially the same direction.

33. The current regulator of claim 31 wherein another of the components is a voltage control device responsive to the voltage regulator so as to maintain the current regulator substantially insensitive to changes in supply voltage.

34. The current regulator of claim 33 wherein the variable resistance varies with temperature in a first direction, and wherein another of the components varies with temperature in substantially the same direction.