Monitoring and Predictive Maintenance
During checkout, ADM even detected a problem the handheld configurator missed. One of our bricks was over-terminated, but not enough to cause a failure. We still had a running system. We weren't getting any communication errors, yet the network was deemed unhealthy by ADM. We had failed to turn off the built-in terminating resistor on one of the bricks. My confidence in advanced diagnostics was starting to grow.
The next system we brought on-line had eight segments. This time, we made sure that the terminators were right and the trunk cables were terminated correctly. After we determined that the segments were good, I used ADM to commission all eight segments. It took only 20 minutes, and identified two problems that my field technicians missed. These errors were corrected in 10 minutes, and the segments were back online and healthy.
After that, we hung 40 instruments on the segments, and used only the diagnostic system to validate. Not one had a problem. Even our longest run, 1,500 feet, came on line with no problem as quickly and as easily as the run that was 5 feet from the cabinet.
Currently we've installed FF using HPT in six different areas. We've stopped using the handheld, and don't haul the oscilloscope out to the field. Once the system is installed, I do the sweep remotely, and we're ready to go.
The physical layer diagnostic module captures snapshots of all values and can store that data for up to two years for long-term trending. Because it has the ability to create a visual representation of the digital fieldbus communications coming from the control room, it truly provides an “extra set of eyes” on communications. In fact, we were having trouble with a valve, and the manufacturer tried to tell me that it was because I had an unhealthy network. I showed him some of the screen shots from the software, and he's never mentioned the health of my network again.
The amount of time that we've saved with advanced diagnostics has been dramatic. It actually takes longer to walk down the system to set the jumper switches and the boxes than it does to commission the system. The physical walk down and commissioning for the first, four-segment system took a day and a half. On the following eight-segment, the physical walk down took about 60 minutes, and the commissioning took just 20 minutes. Our confidence in the network also increased dramatically. When the ADM certifies that the system was good, we know it is good.
In addition, advanced diagnostics has enabled our process to upgrade from incident-based maintenance to predictive maintenance. When you have a plant running 24/7, and an instrument failure of any kind will bring your operation to a standstill, you need a communication system that you can rely on. The ADM-FISCO combination has delivered on every requirement.
Chris Williams is an I&C engineer at Eastman Chemical Co.