Integrating HART data from smart devices
Another solution that uses the HART Protocol is WirelessHART. Using a simple, reliable and secure mesh network, WirelessHART can be viewed as a remote I/O system. Using mesh network technology multiple devices communicate to a gateway that collects all of the process and device diagnostics information and communicates it to a control, asset management or other host system via HART-IP, Modbus TCP, RS485 or others. WirelessHART can be a cost-effective solution for adding new measurements to an existing plant or accessing HART information from existing devices. Typical applications include tank farm monitoring, pipelines, rotating or moving assets, etc.
Many field instruments are now available as native wireless devices, or a wireless adapter can be added to a wired device. Adapters can use the same communication method as a native WirelessHART device.
The latest enhancement to the HART Protocol, HART-IP, defines a standard solution to gain high-speed access to HART device diagnostics and process measurements using a plant's installed networking infrastructure. HART-IP offers the most straightforward way to access all the standard HART information available in a HART device. It allows the information from these devices to be brought up to the Ethernet level easily, without the need to go through any translation processes and with no loss of information. HART-IP can be used for the integration of device information from multiplexer, remote I/O and WirelessHART. When used with WirelessHART, it provides a very cost-effective solution to access measurement information from anywhere in the plant or the enterprise.
Handhelds and single modems
In many situations, a maintenance person or instrumentation engineer may need to configure or check the diagnostic information from an individual field device. There are many types of single HART modems and handheld communicators that can provide an interface easily and inexpensively. Such devices are not limited by manufacturer and can communicate with any instrument or actuator, thanks to the interoperability built into the HART Protocol.
Small single modems can be inserted into a loop whenever needed in the plant or maintenance shop. Such devices can communicate with a laptop or other host system using USB, RS232, or even Bluetooth wireless when a configuration or asset management application is installed.
Today's handheld communicators and calibration tools are hugely versatile and can contain device descriptors for hundreds of devices. The maintenance technician can connect the unit to a field device and it can call up the relevant information from its memory. If necessary, the configuration can be changed or the diagnostic data retained for downloading back at the maintenance shop.
While these individual communication devices can be very useful, they have the inescapable limitation that they require a technician to be involved and can only communicate with one device at a time. By contrast, a fully HART-enabled I/O system can perform all of the above functions on any HART-enabled field instrument or actuator at any time from the control room or maintenance shop.
Work practices: Commissioning and maintenance
When new field devices are going to be installed or brought in for maintenance in the shop, HART Communication can be the means to get them configured properly and tested before returning to operation. The ability to check and verify performance before installation can save an enormous amount of time compared to installing and then removing sensors that aren't ready for use. During the commission phase of a project, HART information can be used to reduce the commissioning time.
Once a new device has had its HART tag name assigned and ranged for that application in the process, it can be ready for the next round of checks where HART information can be provide ease during the checks:
- Verification of the device's location, physically and I/O;
- Configuration and loop check;
- Alarm and interlock validation; and,
- Online operation validation.
Similarly, field instruments and smart valve controllers/positioners can be checked in the shop before returning to operation. A well-developed maintenance program can prescribe a routine of tests tailored to an individual device or group via HART communication to check whatever attributes are most critical. Working through this procedure avoids problems and helps train new technicians.
Once back in place, transmitters and valves can be given final verification before resuming the process. Or, tests can be performed in-situ rather than in the shop. HART can help test a variety of critical attributes, including:
- Verify proper tag and location;
- Verify wiring and power supply;
- Check signal integrity and grounding;
- Re-zero, check range and span calibration;
- Verify analog trim for DCS output;
- Send simulated process variable to verify DCS reading;
- Capture new valve signature for baseline;
- Set alarms and security configuration; and,
- Configure and calibrate additional process variables.
Many device management platforms can record and catalog the results of these tests and adjustments for maintenance recordkeeping.
Work practices: Partial-stroke valve testing
In a plant that is performing well, emergency shutdown (ESD) valves may go for years without having to perform their function. While avoiding upsets and accidents is a good thing, safety protocols require that ESD valves be tested to verify that they still work properly. Valves that aren't operated regularly can fail when called upon due to excessive stem friction, packing problems, air pressure leakage, or other maintenance issues.
ESD valve testing using a full-stroke test (FST) is problematic since cycling these valves can interfere with production. Safety protocols therefore make provisions for partial-stroke testing (PST) of ESD valves in many situations in a way that verifies their performance while minimizing operational disruptions.
Companies that use this technique perform PSTs at regular intervals, allowing for less frequent FSTs. The ways in which ESD valve testing fits into a larger safety program is beyond the scope of this discussion, but once the protocols are established and approved for a given plant, HART-enabled valve positioners and controllers makes PSTs easier to perform and document.
An asset management program can automate the mechanics of PST programs, performing the tests and gathering diagnostic information via HART via this straightforward method:
- Valves are categorized into device groups;
- Program sets schedules in keeping with larger safety system requirements; and,
- Program retains historical data from each test, allowing identification of trends that may indicate developing maintenance problems.
Your next step
Hopefully this discussion has convinced you that there are many ways in which HART Communication can support improved plant performance and asset management. The most difficult step is often making the effort to put it to work. There are many stories of companies that have done it successfully and enjoyed the benefits of higher production and reduced maintenance costs, but implementation requires procedural and often cultural changes among your production, reliability, and maintenance teams.
HART may not deliver all the performance of an advanced fieldbus such as Foundation fieldbus or Profibus PA, but it is much less expensive to implement as it often can use existing instruments and valves.
The issues are not technical since hardware and software solutions are readily available. Often a successful HART-enabled maintenance program can trace its origin to a single enthusiastic individual that emerged as a champion, leading the company into a new period of improved performance and reduced costs.
Amit Ajmeri is a consultant for wireless and field network technology at Yokogawa Corporation of America.
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