RTD measurement unit including detection mechanism for automatic selection of 3-wire or 4-wire RTD measurement mode

• US 20070183478A1
• Filed: 02/06/2006
• Published: 08/09/2007
• Est. Priority Date: 02/06/2006
• Status: Active Grant

• Current Assignee: National Instruments Corporation (Emerson Electric Company)
• Original Assignee: National Instruments Corporation (Emerson Electric Company)
• Inventors: Gartner, Alisa, Becker, Alvin
• Granted Patent: US 7,367,712 B2
• Time in Patent Office: Days
• US Class Current: 374/183
• CPC Class Codes: G01K 15/00 Testing or calibrating of thermometers
• CPC Class Codes: G01K 7/20 in a specially-adapted circuit, e.g. bridge circuit

Abstract

An RTD measurement device including a mechanism for automatic selection of a 3-wire or 4-wire configuration mode of operation. The RTD measurement device may include detection circuitry to detect whether an RTD connected to the RTD measurement device via a plurality of wire connections includes a 3-wire configuration or a 4-wire configuration. The RTD measurement device may include processing circuitry to process one or more readings from the RTD. If a 3-wire configuration is detected, the detection circuitry may automatically configure the processing circuitry to operate in a 3-wire configuration mode. If a 4-wire configuration is detected, the detection circuitry may automatically configure the processing circuitry to operate in a 4-wire configuration mode.

Claims

1. An RTD measurement device comprising:

detection circuitry configured to detect whether an RTD coupled to the RTD measurement device via a plurality of wire connections includes a 3-wire configuration or a 4-wire configuration; and

processing circuitry configured to process one or more readings from the RTD;

wherein, in response to detecting a 3-wire configuration, the detection circuitry is operable to configure the processing circuitry to operate in a 3-wire configuration mode;

wherein, in response to detecting a 4-wire configuration, the detection circuitry is operable to configure the processing circuitry to operate in a 4-wire configuration mode.

2. The RTD measurement device of claim 1, further comprising a resistive element coupled between a first terminal and a second terminal of the RTD measurement device, wherein the detection circuitry is configured to detect a voltage drop across the resistive element to determine whether the RTD includes a 3-wire configuration or a 4-wire configuration.

3. The RTD measurement device of claim 2, wherein, in response to the detection circuitry detecting a voltage drop across the resistive element that is above a predetermined threshold, the detection circuitry is operable to configure the processing circuitry to operate in a 3-wire configuration mode for correcting lead resistance errors.

4. The RTD measurement device of claim 3, wherein, in response to the detection circuitry detecting a voltage drop across the resistive element that is below the predetermined threshold, the detection circuitry is operable to configure the processing circuitry to operate in a 4-wire configuration mode.

5. The RTD measurement device of claim 1, further comprising a switching mechanism coupled to the detection circuitry, wherein the detection circuitry is operable to control the switching mechanism for configuring the processing circuitry to operate in either a 3-wire configuration mode or a 4-wire configuration mode based on the detected RTD configuration.

6. The RTD measurement device of claim 5, further comprising a resistive element coupled between a first terminal and a second terminal of the RTD measurement device, wherein the detection circuitry includes a comparator, wherein a first input terminal of the comparator is coupled to the first terminal of the RTD measurement device and a second input terminal of the comparator is coupled to the second terminal of the RTD measurement device.

7. The RTD measurement device of claim 6, wherein the processing circuitry includes lead resistance compensation circuitry and a conditioning device, and the switching mechanism includes a first switch, wherein a first input terminal of the lead resistance compensation circuitry is coupled to a third terminal of the RTD measurement device, and a second input terminal of the lead resistance compensation circuitry is coupled to a fourth terminal of the RTD measurement device, wherein a first input terminal of the conditioning device is coupled to the second input terminal of the RTD measurement device, and a second input terminal of the conditioning device is coupled to the first switch, wherein the first switch is coupled to the third terminal of the RTD measurement device and to an output terminal of the lead resistance compensation circuitry.

8. The RTD measurement device of claim 7, wherein, in response to detecting a 4-wire configuration, the detection circuitry is operable to configure the first switch in a first position to connect the third terminal of the RTD measurement device to the conditioning device.

9. The RTD measurement device of claim 8, wherein, in response to detecting a 3-wire configuration, the detection circuitry is operable to configure the first switch in a second position to connect the lead resistance compensation circuitry to the conditioning device for correcting lead resistance errors.

10. The RTD measurement device of claim 9, wherein the resistive element comprises a diode.

11. The RTD measurement device of claim 9, wherein the resistive element comprises a first resistor and a second resistor, wherein the switching mechanism comprises the first switch and a second switch, wherein the second switch is coupled to a junction between the first and second resistors and to the second terminal of the RTD measurement device, wherein in response to detecting a 3-wire configuration, the detection circuitry is configured to close the second switch, and wherein in response to detecting a 4-wire configuration, the detection circuitry is configured to open the second switch.

12. The RTD measurement device of claim 2, wherein protection circuitry is coupled to the resistive element to provide over-voltage protection.

13. The RTD measurement device of claim 7, wherein the conditioning device comprises a gain amplifier.

14. The RTD measurement device of claim 2, further comprising an excitation source coupled to the first terminal of the RTD measurement device and to the resistive element.

15. The RTD measurement device of claim 1, wherein, in a 3-wire configuration mode, the processing circuitry is configured to measure a lead resistance error and an initial RTD reading, wherein a corrected RTD reading is derived based on the measured lead resistance error and the initial RTD reading.

16. The RTD measurement device of claim 15, wherein, in a 3-wire configuration mode, a corrected RTD reading is derived by subtracting the measured lead resistance error from the initial RTD reading.

17. The RTD measurement device of claim 1, configured to communicate information indicating whether the RTD coupled to the RTD measurement device includes a 3-wire or 4-wire configuration to a management entity.

18. An RTD measurement device comprising:

detection circuitry configured to detect whether an RTD coupled to the RTD measurement device via a plurality of wire connections includes a first configuration comprising a first number of wire connections or a second configuration comprising a second number of wire connections; and

processing circuitry configured to process one or more readings from the RTD; and

wherein, in response to detecting a first configuration, the detection circuitry is operable to configure the processing circuitry to operate in a first configuration mode;

wherein, in response to detecting a second configuration, the detection circuitry is operable to configure the processing circuitry to operate in a second configuration mode.

19. The RTD measurement device of claim 18, wherein the detection circuitry is configured to detect whether the RTD includes a 3-wire configuration or a 4-wire configuration.

20. The RTD measurement device of claim 19, further comprising a switching mechanism coupled to the detection circuitry, wherein the detection circuitry is operable to control the switching mechanism for configuring the processing circuitry to operate in either a 3-wire configuration mode or a 4-wire configuration mode based on the detected RTD configuration.

21. A method for operating an RTD measurement device, the method comprising:

detecting whether an RTD coupled to the RTD measurement device via a plurality of wire connections includes a 3-wire configuration or a 4-wire configuration;

processing one or more readings from the RTD;

in response to detecting a 3-wire configuration, configuring the RTD measurement device to operate in a 3-wire configuration mode; and

in response to detecting a 4-wire configuration, configuring the RTD measurement device to operate in a 4-wire configuration mode.

22. The method of claim 21, further comprising detecting a voltage drop across a resistive element to determine whether the RTD includes a 3-wire configuration or a 4-wire configuration.

23. The method of claim 22, wherein, in response to detecting a voltage drop across the resistive element that is above a predetermined threshold, configuring the RTD measurement device to operate in a 3-wire configuration mode.

24. The method of claim 23, wherein, in response detecting a voltage drop across the resistive element that is below the predetermined threshold, configuring the RTD measurement device to operate in a 4-wire configuration mode.

25. The method of claim 21, further comprising controlling a switching mechanism for configuring the RTD measurement device to operate in either a 3-wire configuration mode or a 4-wire configuration mode based on the detected RTD configuration.