Input Channel Diagnostics

• US 20120146663A1
• Filed: 02/15/2012
• Published: 06/14/2012
• Est. Priority Date: 02/01/2008
• Status: Active Grant

• Current Assignee: Rockwell Automation, Inc.
• Original Assignee: Rockwell Automation, Inc.
• Inventors: Meagher, Thomas Bruce, Creech, Gerald Robert
• Granted Patent: US 9,256,211 B2
• Time in Patent Office: Days
• US Class Current: 324/549
• CPC Class Codes: G05B 9/02 electric

Abstract

This invention relates to input channel diagnostics for an industrial process control system. The invention provides improved apparatus and methods relating to fault containment, overload protection and input channel diagnostics.

Claims

1-4. -4. (canceled)

5. A field conditioning circuit for receiving a sensor signal and converting said sensor signal to a desired voltage range for use by an input circuit, the field conditioning circuit comprising:

a sense resistor;

a fuse in series with said sense resistor; and

an output for determining when said fuse has blown.

6. A field conditioning circuit according to claim 5 further comprising a Zener diode in series with said fuse and in parallel with a load resistor for providing a load termination wetting current and voltage attenuation.

7. A field conditioning circuit according to claim 5 wherein the sense resistor is further defined as a primary sense resistor and the conditioning circuit includes a secondary sense resistor that is in series with the primary sense resistor.

8. A field conditioning circuit according to claim 7 wherein the output includes:

a primary output that detects a first voltage across the primary sense resistor and the secondary sense resistor; and

a secondary output for detecting a second voltage across the secondary sense resistor.

9. A method of fault detection in a field conditioning circuit for a safety critical system, the method comprising:

receiving an input sense signal from a sensor;

detecting a first output signal from an output of a primary sense resistor that is in series with a secondary sense resistor;

detecting a second output signal from an output of the primary sense resistor;

communicating signals dependent upon the first output signal and the second output signal to a processor for analysis.

10. A method according to claim 9, further comprising:

processing the first output signal with a first high impedance input circuit and an analogue to digital converter; and

processing the second output signal with a second high impedance input circuit and an analogue to digital converter;

prior to communicating the signals to the processor for analysis.

11. A method according to claim 10, further comprising encoding channel specific error checking data and communicating the channel specific error checking data with the signals to a system processor for analysis.

12. A method of internally testing an input channel for a safety critical system, the method comprising:

adding a perturbation signal to an input signal to be applied to an input circuit;

detecting an output signal from the input circuit; and

determining whether addition of said perturbation signal causes a change in said output signal.

13. The method of claim 12 wherein the perturbation signal is determined to be a subliminally scaled amplitude of an operating value of the output signal.

14. The method of claim 12 further comprising storing an input channel identity value locally on at least one channel processor.

15. The method of claim 14 further comprising comparing the input channel identity value to the detected output signal to detect individual channel independence faults.

16. The method of claim 12 wherein the input signal is passed from an input circuit

that includes one or more series resistors that have a total resistance that is at least two orders of magnitude greater than the resistance of a conditioned sensor signal source.

17. The method of claim 16 wherein the series resistors resistance is three orders of magnitude greater than the resistance of the conditioned sensor signal source.

18. The method of claim 16 further comprising low pass noise filtering the conditioned sensor signal source by positioning a low value capacitor in parallel with a signal source voltage.

19. The method of claim 16 further comprising passing the input signal through a fuse that is oriented in series with the one or more series resistors and has an operating threshold that is lower than an operating threshold of the one or more series resistors.

20. The method of claim 19 further comprising providing a load termination wetting current and a voltage attenuation by a Zener diode oriented in series with the fuse and in parallel with one or more series resistors.