By Gary Mintchell, Contributing Editor
If you’re working in a process manufacturing facility, I’m willing to bet that you have instruments containing the HART communication protocol (www.hartcomm.org). This is a fact of life, even if you’re not using it.
The most typical communication for transmitters to control is via the 4-20 mA analog signal. This signal only gives the variation of a value from a process sensor, such as pressure, temperature or flow. Through calibrations, the loop controller or DCS knows the value in real time of that process variable. HART was the first of the widely adopted digital networks. Its adoption was primarily due to its characteristics—the digital information flows over the analog wires.
Cost savings in maintenance
Using built-in diagnostics is the quickest way to enhanced maintenance and production. The diagnostic capabilities of HART‐communicating field devices can eliminate substantial costs by reducing downtime. The HART Protocol communicates diagnostic information to the control room, which minimizes the time required to identify the source of any problem and take corrective action. Trips into the field or hazardous areas are eliminated or reduced.
When a replacement device is put into service, HART communication allows the correct operational parameters and settings to be quickly and accurately uploaded into the device from a central database. Efficient and rapid uploading reduces the time that the device is out of service. Some software applications provide a historical record of configuration and operational status for each instrument. This information can be used for predictive, preventive and proactive maintenance.
HART is also valuable for predicting failures. Take the example of Sasol. It initiated a project where an engineer, responsible for managing communication and control systems across two new chemical plants with a combined 10,000 I/O points, sought a communication solution with the intelligence to predict failures.
In developing the solution, communication was implemented using the HART Protocol in field instruments and a DCS from a preferred vendor. Then, HART technology facilitated a consolidation of hardware and software vendors, and a program to streamline and reduce maintenance-related alarms by 90%. In one area of the site (acrylic acid and acrylates), 4000 HART-enabled devices were used for a seamless diagnostic view for maintenance operations.
Sasol’s new system provides yearly savings estimated at a conservative 6.5 million South African Rand (roughly US$1 million at the time of implementation). HART device-based diagnostic capabilities led to the removal of 40 of 350 non-essential control valves for substantial savings. Detection of faulty or poorly optimized valve positioners likewise led to savings estimated to top two million Rand.
In another example, pressurized tanks at Eastman Chemical Co.’s operation in Longview, TX, may have an allowable working pressure of 63 psig—which could be 10 times more than the span of the tanks’ pressure transmitters. On startup, one tank’s pressure shot up and popped a relief valve. The solution to this problem used only one transmitter with HART technology to replace two originals.
HART technology’s remote configuration capability has helped improve operations at the Texas facility by saving time going to and from the instrument. More importantly, hazardous-area work requires many more permits. Hooking up with HART in the control room is much easier. Remote configuration also allows Eastman to verify field wiring from the control room.
These devices exist. And they’re ready to help you improve maintenance operations.MT
Gary Mintchell (firstname.lastname@example.org) was co-founder and long-time Editor-in-Chief of Automation World magazine. He now writes at www.themanufacturingconnection.com.