DELAYED PUBLISHING IN PROCESS CONTROL SYSTEMS

• US 20130103780A1
• Filed: 10/17/2012
• Published: 04/25/2013
• Est. Priority Date: 10/21/2011
• Status: Active Grant

• Current Assignee: Fisher Controls International LLC (Emerson Electric Company)
• Original Assignee: Fisher Controls International LLC (Emerson Electric Company)
• Inventors: Panther, Mitchell Stephen
• Granted Patent: US 9,002,973 B2
• Time in Patent Office: Days
• US Class Current: 709/213
• CPC Class Codes: H04L 67/12 specially adapted for proprietary or special-purpose networking environments, e.g. medical networks, sensor networks, networks in vehicles or remote metering networks
• CPC Class Codes: H04L 67/568 Storing data temporarily at an intermediate stage, e.g. caching
• CPC Class Codes: H04L 67/62 Establishing a time schedule for servicing the requests

Abstract

Techniques for delaying the publication of data to a network by a device in a process control system or plant include obtaining, at the device, data to be published to the network; storing the obtained data and a corresponding timestamp in a cache; triggering a publication of cached data; and, based on the trigger, publishing the oldest cached data to the network during the publishing timeslot assigned to the device. The cached data may correspond to a sample rate of the device and may include multiple instances of data obtained over time. The device includes a network interface, a cache, and a publisher, and the device may be configured to operate in the delayed publishing mode, or to operate in an immediate publishing mode in which currently obtained data that has not been cached is published to the network during the publishing time slot assigned to the device.

Claims

1. A network device communicatively coupled to a process control system, comprising:

a connection to a network included in the process control system;

a publisher configured to publish data to the network of the process control system during a publishing timeslot allocated to the network device, wherein the data corresponds to a process controlled in the process control system; and

a cache storing one or more entries, each entry of the one or more entries including a value of the data corresponding to the process and a respective timestamp,

wherein the publisher is triggered to publish, to the network via the connection and during the publishing timeslot, contents of a particular entry of the cache that includes a particular timestamp corresponding to an instance in time that occurred prior to the publishing timeslot.

2. The network device of claim 1, wherein the one or more entries of the cache correspond to a sample rate of the network device.

3. The network device of claim 2, wherein the sample rate is configurable.

4. The network device of claim 1, wherein the publishing timeslot is included in a plurality of publishing timeslots allocated to the network device, and wherein at least one entry of the cache includes a respective timestamp indicating an instance in time that occurred after an occurrence of a first publishing timeslot and before an occurrence of a second publishing timeslot immediately subsequent to the first publishing timeslot.

5. The network device of claim 1, wherein the network supports a HART protocol.

6. The network device of claim 5, wherein the HART protocol is a wireless HART protocol.

7. The network device of claim 1, wherein the data corresponding to the process corresponds to a process control event.

8. The network device of claim 7, wherein the process control event corresponds to a particular state, the particular state included in a set of two or more states.

9. The network device of claim 1, wherein the publishing timeslot allocated to the network device is indicated by a network manager coupled to the network, and wherein the publisher is triggered to publish the contents of the particular entry to the network manager via the network.

10. The network device of claim 1, wherein:

the entry stored in the cache is an oldest active entry stored in the cache,

the oldest active entry is determined based on the respective timestamp included in the oldest active entry, and

the oldest active entry is deactivated after publishing.

11. A method of delaying publication of data by a network device in a process control system, comprising:

receiving, at the network device coupled to a network included in the process control system, an indication of a publishing timeslot assigned to the network device;

independent of an occurrence of the publishing timeslot, obtaining, at the network device, data to be published to the network, the data corresponding to a process being controlled in the process control system;

storing, in an entry of a cache of the network device, the data to be published to the network and a timestamp corresponding to the data;

triggering a publication of the data corresponding to the process, including determining an oldest entry of the cache; and

publishing, by the network device, contents of the oldest entry of the cache to the network.

12. The method of claim 11, wherein obtaining the data corresponding to the process comprises at least one of:

obtaining data corresponding to an event associated with the process, or obtaining a value of a parameter associated with the process.

13. The method of claim 11, wherein:

obtaining the data to be published to the network comprises obtaining multiple values over time of the data to be published to the network in accordance with a sample rate corresponding to the network device, and

storing, in the entry of the cache, the data to be published to the network and the timestamp corresponding to the data comprises storing, in a different entry of the cache, each value of the multiple values of the data and a timestamp corresponding to the each value.

14. The method of claim 13, further comprising configuring the sample rate corresponding to the network device.

15. The method of claim 11, wherein:

obtaining the data to be published to the network comprises obtaining the data to be published to the network in accordance with a sample rate corresponding to the network device, and

a rate of re-occurrence of the publishing timeslot is less than the sample rate corresponding to the network device.

16. The method of claim 11, wherein the network is a wireless HART network, and wherein publishing the contents of the oldest entry of the cache to the network comprises transmitting, using a wireless HART protocol, the contents of the oldest entry of the cache to a network manager coupled to the network.

17. The method of claim 11, wherein:

the network device is operable in a first mode and in a second mode;

when the network device is operating in the first mode, triggering the publication of the data corresponding to the process comprises triggering the publication of the data corresponding to the process during the publishing timeslot, and publishing the contents of the oldest entry of the cache to the network comprises publishing the contents of the oldest entry of the cache to the network during the publishing timeslot; and

when the network device is operating in the second mode, triggering the publication of the data corresponding to the process comprises;

forgoing determining the oldest entry of the cache,

forgoing publishing the contents of the oldest entry of the cache to the network, and

determining a current value of the data corresponding to the process and publishing the current value of the data corresponding to the process to the network during the publishing timeslot.

18. The method of claim 17, further comprising at least one of configuring the network device to operate in the first mode, or configuring the network device to operate in the second mode.

19. The method of claim 11, wherein:

triggering the publication of the data corresponding to the process comprises triggering the publication of the data corresponding to the process during the publishing timeslot, and

publishing, by the network device, the contents of the oldest entry of the cache to the network comprises publishing, by the network device, the contents of the oldest entry of the cache to the network during the publishing timeslot.

20. A network device operating in a process control system, comprising:

a processor;

a cache;

a network interface coupling the network device to a communications network included in the process control system;

a process control interface configured to obtain values of a parameter corresponding to a process control function;

a tangible, non-transitory memory having instructions stored thereon that are executable by the processor to;

receive an indication of a publishing timeslot allocated to the network device;

when the network device is operating in a first mode, during the publishing timeslot;

obtain, via the process control interface, a current value of the parameter corresponding to the process control function, and

publish, to the communications network via the network interface, the current value of the parameter; and

when the network device is operating in a second mode,

publish, during the publishing timeslot to the communications network via the network interface, contents of an oldest active entry stored in the cache, the contents of the oldest active entry including a previously obtained value of the parameter corresponding to the process control function, wherein the previously obtained value was obtained at an instance in time occurring prior to the publishing timeslot; and

deactivate the oldest active entry after publishing the oldest active entry.

21. The network device of claim 20, wherein the instructions are further executable by the processor to:

store each value of the values of the parameter corresponding to the process control function in a different entry of the cache; and

store a timestamp corresponding to the each value in the different entry of the cache.

22. The network device of claim 21, wherein:

the values of the parameter received by the process control interface are obtained based on a sample rate of the network device,

at least one value of the parameter is obtained at the process control interface of the network device prior to an occurrence of a next publishing timeslot allocated to the network device, and

the instructions are further executable by the processor to store each at least one value of the parameter and a respective timestamp in a respective entry of the cache when the network device is operating in the second mode.

23. The network device of claim 20, wherein the values of the parameter corresponding to the process control function are generated by a field device.

24. The network device of claim 20, wherein the communications network is a wireless HART communications network.