PROCESS VARIABLE MEASUREMENT NOISE DIAGNOSTIC

• US 20140095095A1
• Filed: 09/28/2012
• Published: 04/03/2014
• Est. Priority Date: 09/28/2012
• Status: Active Grant

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Rud, Jason Harold, Engelstad, Loren Michael
• Granted Patent: US 9,602,122 B2
• Time in Patent Office: Days
• US Class Current: 702/69
• CPC Class Codes: G05B 23/0221 Preprocessing measurements, e.g. data collection rate adjustment; Standardization of measurements; Time series or signal analysis, e.g. frequency analysis or wavelets; Trustworthiness of measurements; Indexes therefor; Measurements using easily measured parameters to estimate parameters difficult to measure; Virtual sensor creation; De-noising; Sensor fusion; Unconventional preprocessing inherently present in specific fault detection methods like PCA-based methods
• CPC Class Codes: H03M 1/1071 Measuring or testing

Abstract

A process variable transmitter, includes an analog-to-digital (A/D) converter that receives a sensor signal provided by a sensor that senses a process variable and converts the sensor signal to a digital signal. A processor receives the digital signal and provides a measurement output indicative of the digital signal. A noise detector receives the sensor signal and generates a first value indicative of a number of positive noise events relative to a positive threshold value and a second value indicative of a number of negative noise events relative to a negative threshold value. The processor evaluates the noise count and generates a noise output, indicative of detected noise, based on the first and second values.

Claims

1. A process variable transmitter, comprising:

an analog-to-digital (A/D) converter receiving a sensor signal provided by a sensor that senses a process variable and converts the sensor signal to a digital signal;

a processor that receives the digital signal and provides a measurement output indicative of the digital signal; and

a noise detector that receives the sensor signal and generates a first value indicative of a number of positive noise events relative to a positive threshold value and a second value indicative of a number of negative noise events relative to a negative threshold value, the processor evaluating the noise count and generating a noise output, indicative of detected noise, based on the first and second values.

2. The process variable transmitter of claim 1 wherein the noise detector comprises:

a positive noise threshold generator that receives the sensor signal and generates the positive threshold value as a positive voltage threshold; and

a negative noise threshold generator that receives the sensor signal and generates the negative threshold value as a negative voltage threshold.

3. The process variable transmitter of claim 2 wherein the noise detector further comprises:

a positive noise counter that receives the sensor signal, a clock input and the positive voltage threshold and accumulates a positive count with each clock pulse on the clock signal when the sensor signal exceeds the positive voltage threshold in a positive direction.

4. The process variable transmitter of claim 3 wherein the noise detector further comprises:

a negative noise counter that receives the sensor signal, a clock input and the negative voltage threshold and accumulates a negative noise count with each clock pulse on the clock signal when the sensor signal exceeds the negative voltage threshold in a negative direction.

5. The process variable transmitter of claim 4 wherein the processor generates the noise output based on the positive and negative noise counts.

6. The process variable transmitter of claim 5 wherein the processor generates the noise output as a characterization of noise based on the positive and negative noise counts.

7. The process variable transmitter of claim 6 wherein the processor generates the characterization of noise as the A/D converter is converting the sensor signal to the digital signal.

8. The process variable transmitter of claim 6 wherein the processor generates the noise output by analyzing the positive and negative noise counts to identify noise symmetry, noise frequency and noise level.

9. The process variable transmitter of claim 7 wherein the A/D converter converts the sensor signal to the digital signal over a settling time and wherein the processor generates the noise output to identify whether settling time is contributing to measurement inaccuracies.

10. The process variable transmitter of claim 6 wherein the processor generates a noise profile for the process variable transmitter based on characterizations of the noise over time.

11. The process variable transmitter of claim 2 wherein the processor intermittently latches the sensor signal across a storage capacitor and wherein the positive and negative noise threshold generators receive, as the sensor signal, the voltage across the storage capacitor.

12. The process variable transmitter of claim 11 wherein the noise detector further comprises:

a refresh counter, wherein the processor refreshes the sensor signal latched across the storage capacitor based on an output from the refresh counter.

13. The process variable transmitter of claim 1 wherein the noise detector is a part of the A/D converter.

14. The process variable transmitter of claim 1 wherein the noise detector is separate from the A/D converter.

15. The process variable transmitter of claim 1 wherein the processor provides the measurement output over a process control loop.

16. The process variable transmitter of claim 1 wherein the sensor comprises at least one temperature sensor selected from a group comprising a resistive temperature device and a thermocouple.

17. The process variable transmitter of claim 1 wherein the noise output is indicative of line noise.

18. The process variable transmitter of claim 1 wherein the noise detector monitors noise from a plurality of sensor signals.

20. The method of claim 17 wherein accumulating positive noise counts comprises generating the positive noise threshold based on the sensor signal and wherein accumulating negative noise counts comprises generating the negative noise threshold based on the sensor signal.

21. The method of claim 18 wherein generating the output indicative of characterization of the noise comprises:

generating the output to identify at least one of an estimate of noise symmetry, noise frequency, noise level, a source of the noise, and a noise profile for the process variable transmitter.

19. A method of sensing a process variable in a process variable transmitter, comprising:

receiving an analog sensor signal from a sensor indicative of the process variable;

converting the analog sensor signal to a digital signal;

during conversion of the analog sensor signal to the digital signal, accumulating positive noise counts in a positive noise accumulator, indicative of noise events that exceed a positive noise threshold, accumulating negative noise counts in a negative noise, accumulator, indicative of noise events that exceed a negative noise threshold;

characterizing noise on the analog sensor signal based on the positive noise counts and the negative noise counts; and

generating an output on a process control loop indicative of the digital signal and the characterization of the noise on the analog sensor signal.

22. A process variable transmitter, comprising:

an analog-to-digital (A/D) converter receiving a temperature sensor signal provided by a temperature sensor that senses a process temperature and converts the temperature sensor signal to a digital signal;

a processor that receives the digital signal and controls current on a process control loop to provide a measurement output indicative of the digital signal; and

a noise detector that receives the temperature sensor signal and generates, during conversion of the temperature sensor signal to the digital signal, a first count value indicative of a number of positive noise events relative to a positive threshold value and a second count value indicative of a number of negative noise events relative to a negative threshold value, the processor generating a noise output, indicative of a characteristic of detected noise, based on the first and second count values.