There are ways to do external control valve monitoring without spending a lot of money. With a smart positioner, you can get relevant information about the health of your control valve. Usually, all diagnostics die in the field because most applications only read the analog output. But this can be avoided by using the HART communication protocol and a HART multiplexer.
The benefits of HART
Implementing an asset management system that covers field instrumentation in a process plant environment requires some type of smart device platform. Since most modern field devices provide HART communication capability in addition to the analog process variable, plants may have to weigh approaches employing either traditional or integrated HART I/O as part of the decision to move to an instrument asset management system.
In any Distributed Control Systems (DCS), integrating an asset management system requires a means of connecting the asset management software to the HART I/O and on to the devices. While the basic protocol is pretty much the same in all control systems, the mechanism for this integration is normally proprietary, with each vendor choosing an implementation approach that works best for them. There’s a lot of room for some “secret sauce” to make better use of the limited bandwidth available with the HART protocol.
Field Device Tool/Device Type Manager (FDT/DTM)
Many automation equipment suppliers now use FDT/DTM (Field Device Tool/Device Type Manager) technology so they can present more meaningful device information. DTMs are software components that contain device-specific data, functions, and logic elements. They can range from a simple graphical user interface for setting device parameters to highly sophisticated applications that perform complex calculations for diagnostics and maintenance purposes or implement complex business logic for device calibration. The DTM also contains interfaces to enable communication with the connected system or tool.
Device suppliers are able to embed intelligence in a DTM in a way that is very difficult to accomplish with DD files, such as a number of graphical constructs that cannot be expressed within DD technology. Moreover, the DTM is device and revision specific so that it has knowledge about the particular version of each device on the control network. It is interesting that the automation industry attaches so much importance to the IAMS, when it is the contents of the DTM that really have value for the end-user. The IAMS is simply a container enabling communications to the devices, a way to organize information, as well as a path to the technician or operator.
Valve Manager for HART Multiplexer Networks is a Windows-based graphical user interface for a valve controller. Valve Manager for HART Multiplexer Networks makes the connection to the devices through HART multiplexers. This allows several hundreds of devices to be connected into a single serial port of the PC. With Valve Manager the following functions included in the smart positioner can be accessed:
- On-line monitoring
- Diagnostics: trends and alerts
- Control valve testing
How to monitor a control valve using a HART multiplexer
If you don’t have a HART control system, then you can collect the information by installing a multiplexer between the field devices and the control system. Still, that requires a lot of structure and procedure.
Below you have a video explaining the hart protocol in more details :
You also have the option of installing a wireless adapter on your control valves to collect the HART signal and send the diagnostic through wireless communication. You can find a broad range of options on the market using two principal protocols, the WirelessHART and ISA100. Depending on the protocol, you can gain other options based on brands and interoperability.
Installing a wirelessHART won’t make your valve wireless. But the simple installation won’t affect the analog output from the adapter.
The video below explains the wireless HART principle:
If you would like to know more about control valve monitoring or the HART multiplexer, give us a call and our experts will help