Control valve diagnostics using hart
Figure 2. Maintenance without diagnostics costs more than three times as much as that done using diagnostic data.Bereznai believes that the significant cost differential between wiring the diagnostics-laden HART cable to a new multiplexer and using the THUM adapters will mean that they can keep their existing devices longer.
Valve diagnostics are the most important thing, he believes. "There is a huge benefit. Predictive notification can save $7000 to $100,000 or more by avoiding unplanned outages. At our facility, our most important product is diesel. One day's diesel production is worth $300,000. In 2011, we avoided a one-day outage. You can see why this is important."
To make it work, Bereznai adds his team involved everyone. "Everybody needs asset management," he says, "and it's very important to involve everybody. There were many skeptics at first, but now they're believers."
How did Bereznai and his team get started? "First, we got high level buy in," he says. "Then we standardized on HART and later Foundation fieldbus devices. Then we put together a maintenance strategy plan and an action plan. We have a living contract with our three DCS vendors to maintain the systems and keep them current. And finally, we did training. Maintenance involves all the staff, and everybody does it."
Extracting diagnostic signals is one of the key use cases for wireless mesh networks in process plants. It would seem to be a no-brainer to jump in and start enabling wireless systems, but like MOL, most users are still doing pilot projects.
One of the reasons for this is the multiplicity (still) of wireless sensor network standards. WirelessHART, now IEC62591-WirelessHART, was the first IEC international standard, but it won't be the last. ISA100.11a will eventually be approved as a global standard, as will WIA-PA, the Chinese national standard.The ISA100.12 convergence process has been abandoned, and if end users buy some of each standard, they may actually be setting themselves up for unsafe practices and accidents. ISA100.11a devices do not interoperate with WirelessHART devices. They are not interchangeable with WirelessHART devices. And at this point, due to the failure of ISA100.12, there is no intention of making them either interchangeable or interoperable.
So what happens when a critical transmitter or wireless digital valve positioner fails during an important process condition like an upset? Somebody is detailed to run into the stores shed, get another transmitter, and go put it in . At 3 a.m., in upset conditions, it could be very easy to grab the transmitter that is not the one that is going to work in that application. This might cause an upset to become a disaster.
It isn't clear yet how much foothold WIA-PA will have, either inside or outside of China, but the other wireless mesh network standard, Zigbee, is making a substantial comeback.
Zigbee was investigated thoroughly by both the HART and ISA100 teams (they had many of the same members), and found not robust enough for the process industries. Unfortunately, the U.S. government decided that Zigbee would be a grand choice for the wireless sensor protocol for the Smart Grid.
Recently, several valve actuator and positioner indicator companies have decided to use Zigbee instead of WirelessHART. Even a SCADA company, exemys, headquartered in Argentina, but selling worldwide, has standardized on Zigbee for its substation and pumping station wireless mesh networks.
So even though MOL and others have shown that there are significant reasons to use wireless mesh networks, the end users remain skeptical.