Wireless Communication of Process Measurements

• US 20080082180A1
• Filed: 09/06/2007
• Published: 04/03/2008
• Est. Priority Date: 10/25/2005
• Status: Active Grant

• Current Assignee: Fisher-Rosemount Systems Incorporated (Emerson Electric Company)
• Original Assignee: Fisher-Rosemount Systems Incorporated (Emerson Electric Company)
• Inventors: Nixon, Mark, Karschnia, Robert, Blevins, Terrence
• Granted Patent: US 8,719,327 B2
• Time in Patent Office: Days
• US Class Current: 700/29
• CPC Class Codes: G05B 11/42 for obtaining a characteristic which is both proportional and time-dependent, e.g. P. I., P. I. D.
• CPC Class Codes: G05B 15/02 electric
• CPC Class Codes: G05B 2219/31162 Wireless lan
• CPC Class Codes: G05B 2219/34413 Add time stamp to command message
• CPC Class Codes: G05B 2219/37526 Determine time or position to take a measurement
• 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: H04L 43/16 Threshold monitoring

Abstract

A method and device or monitoring parameters in a process reduces power consumption and bandwidth requirements in the transmission of the monitored parameter to for example, a monitoring application. In particular, new monitoring parameter values are only transmitted if the difference between a measured or calculated parameter value and the most recently transmitted value exceeds a limit, since the last communication of the parameter or if the time since the last communication of the parameter exceeds a preset refresh period. The determination as to whether to transmit the parameter can be applied to engineering unit values or raw values.

Claims

1. A system for monitoring a process, comprising:

a communication network;

a monitoring application located in a first device communicatively connected to the communication network; and

a process control device communicatively connected to the communication network;

wherein said process control device includes a processing unit that operates to obtain a series of values for a monitored parameter, compare a new value of the monitored parameter to a previous value of the monitored parameter for which a monitored signal was previously transmitted to the monitoring application to create a difference signal, compare the difference signal to a difference threshold and transmit a further monitored signal indicative of the new value of the monitored parameter to the monitoring application via the communication network when the difference signal exceeds the difference threshold.

2. The system of claim 1, wherein the processing unit of the process control device further operates to compute a time difference between a current time and a time associated with the monitored signal previously transmitted to the monitoring application, compare the time difference to a time threshold and transmit the further monitored signal indicative of the new value of the monitored parameter to the monitoring application via the communication network when the time difference exceeds the time threshold even if the difference signal does not exceed the difference threshold.

3. The system of claim 1, wherein the processing unit of the process control device further operates to compute a time difference between a current time and a time associated with the monitored signal previously transmitted to the monitoring application, compare the time difference to a time threshold and transmit a heartbeat signal indicating the operability of the communication network to the monitoring application via the communication network when the time difference exceeds the time threshold even if the difference signal does not exceed the difference threshold.

4. The system of claim 1, wherein the new value of the monitored parameter and the previous value of the monitored parameter are expressed in raw units, and wherein the processing unit of the process control device converts the new value of the monitored parameter to a new unit scale when the difference signal exceeds the difference threshold, and wherein the further monitored signal indicative of the new value of the monitored parameter includes the new value of the monitored parameter converted to the new unit scale.

5. The system of claim 1, wherein the new value of the monitored parameter and the previous value of the monitored parameter are expressed in raw units, and wherein the processing unit of the process control device converts the new value of the monitored parameter to a new unit scale only when sending the further monitored signal indicative of the new value of the monitored parameter to the monitoring application via the communication network.

6. The system of claim 1, wherein the process control device is a field device.

7. The system of claim 1 wherein the process control device is a sensor and the monitored parameter is a measured process variable.

8. The system of claim 1, wherein the process control device includes a computational unit that computes a variable value using multiple inputs, and wherein the monitored parameter is the computed variable value.

9. The system of claim 8, wherein one of the multiple inputs is a measured process variable.

10. The system of claim 1 wherein the communication network is a wireless communication network.

11. The system of claim 1, wherein the processing unit obtains the series of values for the monitored parameter as a set of regularly spaced-in-time values of the monitored parameter.

12. A method of monitoring a process, comprising:

obtaining a value for a monitored signal at a plurality of times;

computing a difference signal indicative of a difference between a value of the monitored signal collected at a first time and a value of the monitored signal for which a signal was previously transmitted to a monitoring unit via a communication network;

comparing the difference signal to a difference threshold; and

transmitting a signal indicative of the value of the monitored signal collected at the first time to the monitoring unit via the communication network if the difference signal exceeds the difference threshold.

13. The method of claim 12, further comprising converting the value of the monitored signal collected at the first time from raw units to a representation of the monitored signal in engineering units to produce the signal indicative of the value of the monitored signal collected at the first time when the difference signal exceeds the difference threshold.

14. The method of claim 12, wherein transmitting the signal indicative of the value of the monitored signal collected at the first time includes wirelessly transmitting the signal indicative of the value of the monitored signal collected at the first time to the monitoring unit via a wireless communication channel.

15. The method of claim 12) further including tracking an elapsed time associated with a signal indicative of a value of the monitored signal previously transmitted to the monitoring unit via a communication network, comparing the elapsed time to a time threshold and transmitting the signal indicative of the value of the monitored signal collected at the first time to the monitoring unit via the communication network if the elapsed time is greater than the time threshold even if the difference signal does not exceed the difference threshold.

16. The method of claim 12, wherein obtaining the value for the monitored signal at the plurality of times includes obtaining a computed data value at each of the plurality of times.

17. The method of claim 12, wherein computing the difference signal indicative of the difference between the value of the monitored signal collected at the first time and the value of the monitored signal for which a signal was previously transmitted to the monitoring unit via the communication network includes comparing the value of the monitored signal collected at the first time and the value of the monitored signal previously transmitted to the monitoring unit as expressed in raw units.

18. The method of claim 12, further including:

obtaining a value for a second monitored signal at a second plurality of times within a same field device that obtains the value for the monitored signal at the plurality of time;

computing a second difference signal indicative of a difference between a value of the second monitored signal collected at a first time and a value of the second monitored signal for which a signal was previously transmitted to a monitoring unit via a communication network;

comparing the second difference signal to a second difference threshold; and

transmitting a second signal indicative of the value of the second monitored signal collected at the first time to the monitoring unit via the communication network if the second difference signal exceeds the second difference threshold.

19. The method of claim 12, wherein computing the difference signal indicative of the difference between the value of the monitored signal collected at the first time and the value of the monitored signal for which a signal was previously transmitted to the monitoring unit via the communication network includes comparing the value of the monitored signal collected at the first time and the value of the monitored signal previously transmitted to the monitoring unit in engineering units.

20. A method of monitoring a process, comprising:

measuring a process parameter at each of a plurality of times;

computing a difference signal indicative of a difference between a magnitude of the process parameter measured at a recent one of the plurality of times and a magnitude of the process parameter measured at a previous one of the plurality of times;

comparing the difference signal to a difference threshold; and

if the difference signal is greater than the difference threshold, converting the magnitude of the process parameter for the recent one of the plurality of times to a different scale and transmitting the converted magnitude of the process parameter for the recent one of the plurality of times to a monitoring unit via a communication network.

21. The method of claim 20, wherein transmitting the converted magnitude of the process parameter for the recent one of the plurality of times to the monitoring unit includes transmitting the converted magnitude of the process parameter for the recent one of the plurality of times to the monitoring unit via a wireless communication network.

22. The method of claim 21, wherein converting the magnitude of the process parameter for the recent one of the plurality of times to a different scale includes converting the magnitude of the process parameter to a magnitude expressed in engineering units indicative of the physical nature of the process parameter.

23. The method of claim 22, further including tracking an elapsed time between a time associated with the process parameter for the recent one of the plurality of times and a time associated with a previous converted magnitude of the process parameter which was transmitted to the monitoring unit, comparing the elapsed time to a time threshold and, if the elapsed time is greater than the time threshold;

(1) converting the magnitude of the process parameter for the recent one of the plurality of times to a different scale, and

(2) transmitting the converted magnitude of the process parameter for the recent one of the plurality of times to the monitoring unit via the communication network.

24. The method of claim 23, wherein the time associated with the process parameter for the recent one of the plurality of times is a time at which the process parameter for the recent one of the plurality of times was measured, and wherein the time associated with the previous converted magnitude of the process parameter which was transmitted to the monitoring unit is a time at which the process parameter associated with the previous converted magnitude of the process parameter was measured.

25. The method of wirelessly transmitting data within a process plant, comprising:

monitoring one or more parameter values within the process plant at a plurality of times;

performing an analysis using the one or more monitored parameter values to produce an analysis output associated with each of the plurality of times;

computing a difference signal indicative of a difference between a value of the analysis output associated with a first one of the plurality of times and an analysis output associated with a previous one of the plurality of times for which one or more analysis signals were previously transmitted to a monitoring unit via a wireless communication network; and

determining whether to send one or more analysis signals associated with the analysis for the first one of the plurality of times via the wireless communication network based on the difference signal.