Beyond basics

Asset management software pushes advanced diagnostics.

Plant control system operators and maintenance technicians have a ton of responsibilities. They must make sure the process is running optimally and make sure instruments that control the process are also performing properly.

Over the past few years, the importance of asset management has received a lot of attention. More than a quarter of maintenance dollars are spent on instruments and valves (27%, compared to 24% on mechanical equipment and 24% on process equipment), according to some industry data. Quite a few companies have implemented software applications to assist with managing smart transmitters and valves.

Typically, the software runs basic diagnostic functions and troubleshooting, making changes to the device's parameters and configuration and managing device calibration. These software applications also automatically document changes to the devices, for keeping historical records.

As workers have become more comfortable with using software for asset management (in place of traditional paper records), users have been looking to expand the capabilities. Specifically, the area of advanced diagnostics has been the main focus. As plants move away from reactive maintenance practices, which are costly and time consuming, users need tools to allow for predictive maintenance. They want to know which instruments need attention and the exact requirements for what type of work or repair they need to do. The scope of asset management software has expanded to include the ability for advanced diagnostics.

Smart devices

Asset management in a plant environment has come to mean managing the smart transmitters and valves, making sure they are configured and performing as specified. Smart digital protocols allow access to much more than just the device's process variable. These devices can be set up on a network to transmit live information about themselves and the process in which they are used. The information is stored in the asset management software. "Real-time" information along with the historical records in the software give users a chance to see the big picture, and make decisions based on all the data.

Proper management of smart assets is important throughout the life cycle of a plant, and the use of software tools is key. During the start-up of a new plant, or even just a few new devices, software can quickly build up a database of devices, perform loop checks and basic calibration methods, and confirm proper wiring and configuration of the devices. These can all happen faster than they can with traditional start-up practices. For ongoing maintenance tasks, the software troubleshoots devices; changes and compares device configurations; defines, schedules, and documents calibration records; and keeps the history of all devices. All of this leads to an increase in the plant's throughput and availability, improved product quality, and lower costs for maintenance and operations.

Advanced diagnostics

Maintenance engineers agree that calibrating and performing troubleshooting on valves is very time consuming. Because valves are critical in the control loop, they receive a lot of attention. The downside of this can be a user spends too much money and time working on valves that do not require maintenance. As plants strive to be proactive, it is not uncommon for them to have annual or semiannual overhauls of all valves, not knowing if they need it or not. Today, however, technicians use the advanced features in their asset management system to perform tests on HART or Foundation fieldbus digital valve controllers connected to the valves. Technicians can diagnose specific problems quickly and easily, and workers only spend time on the valves that require maintenance. Also, because the diagnostics and calibrations can run while the valve is in service, the tests can run and catch potential problems before they affect the rest of the process.

One such diagnostic is the valve signature. This test is usually run when a valve is new to benchmark its performance, trending the travel distance when opening and closing versus the pressure applied. As users perform the test over the years, they can overlay the results on the original, determine actuator spring rate and valve friction, and see if any degradation has occurred, such as problems with the packing. Other features may include the following:

* step response test, to minimize overshoot, dead band, and dead time

* dynamic error band test, to determine how the valve will perform under dynamic conditions

* calculation of friction, spring rate, and other parameters, to give the user the best possible view into the health of the valve

* tuning and calibration, to set up the valve properly and quickly during commissioning

All of this information helps users pinpoint exactly what needs repair, instead of replacing parts that are still good. Weyerhaeuser in Grande Prairie, Alberta, Canada, used the advanced valve diagnostics in its asset management software and realized savings of more than $19,000 (CAN$26,000) during one scheduled shutdown.