NOISE DETECTION AND AVOIDANCE

• US 20120041704A1
• Filed: 08/01/2011
• Published: 02/16/2012
• Est. Priority Date: 08/11/2010
• Status: Active Grant

• Current Assignee: Micro Motion Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Foss, Scot R., Rovner, Bruce D.
• Granted Patent: US 9,057,634 B2
• Time in Patent Office: Days
• US Class Current: 702/100
• CPC Class Codes: G01F 1/60 Circuits therefor
• CPC Class Codes: G01F 1/72 Devices for measuring pulsing fluid flows

Abstract

A process variable transmitter includes a sensor drive controller that outputs a sensor drive signal that is used to drive a sensor that senses a process variable. The sensor drive controller changes the frequency of the sensor drive signal to avoid frequencies and associated harmonics at which noise occurs and which could interfere with the sensor signal.

Claims

1. A method of using a process variable transmitter to control a process variable sensor that senses a process variable in a running process, the method comprising:

applying a sensor control signal to the process variable sensor;

receiving a sensor signal from the process variable sensor related to the process variable, the sensor control signal and noise in the process;

adjusting a sensor control signal frequency of a sensor control signal to reduce an effect of the noise in the process; and

controlling the process variable sensor at the adjusted sensor control signal frequency.

2. The method of claim 1 wherein adjusting the sensor control signal frequency comprises:

periodically shifting a phase of the sensor control signal frequency to cancel the noise.

3. The method of claim 2 wherein periodically shifting comprises:

periodically shifting the phase of the sensor control signal by 180 degrees.

4. The method of claim 1 and further comprising:

detecting a noise frequency at which noise occurs on the sensor signal; and

wherein adjusting the sensor control signal frequency comprises adjusting the sensor control signal frequency based on the detected noise frequency.

5. The method of claim 4 and further comprising:

prior to detecting the noise frequency, detecting frequency characteristics of the sensor control signal; and

storing the frequency characteristics.

6. The method of claim 5 and further comprising:

after detecting the noise frequency, comparing the noise frequency to the frequency characteristics of the sensor control signal.

7. The method of claim 6 and further comprising:

adjusting the sensor control signal frequency if the noise frequency is sufficiently close to the frequency characteristics of the sensor control signal.

8. The method of claim 7 wherein adjusting the sensor control signal frequency comprises:

adjusting the sensor control signal frequency so that it is sufficiently far away from the noise frequency to avoid substantial interference with the sensor signal.

9. The method of claim 7 wherein adjusting the sensor control signal frequency comprises:

randomly changing the sensor control signal frequency within a desired range of frequencies.

10. The method of claim 7 wherein adjusting the sensor control signal frequency comprises:

detecting a period of the noise frequency; and

applying a filter to the sensor control signal to filter components of the sensor control signal to filter out periodic noise occurring at the period of the noise frequency.

11. The method of claim 4 and further comprising:

prior to detecting the noise frequency, intermittently disabling the sensor control signal and then detecting the noise frequency.

12. The method of claim 4 and further comprising:

prior to detecting the noise frequency, disabling the sensor control signal in response to a user request and then detecting the noise frequency in response to a user request to detect the noise frequency.

13. A process variable transmitter receiving a sensor signal from a process variable sensor and controlling the sensor using a control signal, the transmitter comprising:

a noise detector detecting noise, having a noise frequency, on the sensor signal;

a controller generating the control signal at a control frequency; and

a processor, coupled to the noise detector and the controller, configured to adjust the control frequency based on the noise frequency.

14. The process variable transmitter of claim 13 and further comprising:

a frequency characteristics data store, the processor identifying frequency characteristics of the control signal and storing the frequency characteristics in the frequency characteristics data store.

15. The process variable transmitter of claim 14 wherein the processor identifies the frequency characteristics of the control signal as a ratio of the control frequency to harmonics of the control frequency.

16. The process variable transmitter of claim 13 wherein the processor adjusts the control frequency by randomly changing the control frequency within a desired range of frequencies.

17. The process variable transmitter of claim 13 wherein the processor periodically phase shifts the control frequency by 180 degrees.

18. A process variable transmitter receiving a flow signal, from a magnetic flow meter, indicative of flow of a process fluid through a conduit, the process variable transmitter comprising:

a coil drive controller generating a coil drive signal to drive coils on the magnetic flow meter at a coil drive frequency;

a noise detector detecting periodic noise, having a noise frequency, on the flow signal; and

a processor configured to intermittently disable the coil drive signal so the noise detector can detect the periodic noise, compare the noise frequency to stored frequency characteristics of the coil drive signal, and adjusting the coil drive frequency, based on the comparison, to thereby avoid substantial interference of the periodic noise with the flow signal.

19. The process variable transmitter of claim 18 and further comprising:

a frequency data store, wherein the processor identifies the frequency characteristics of the coil drive signal and stores them in the frequency data store.

20. The process variable transmitter of claim 18 wherein the process variable transmitter receives additional sensor signals from additional sensors indicative of other sensed process variables, wherein the noise detector detects periodic noise, at a noise frequency, on the additional sensor signals and wherein the processor adjusts sensor control signals, for controlling the additional sensor signals, based on a comparison of frequency characteristics of sensor control signals for the additional sensors and the noise frequency of the periodic noise detected on the additional sensor signals.