Tracking Down Intermittent Flow Measurement Issues

Emerson’ Steve Moore, a wireless specialist for Rosemount wireless measurement devices told a great story of finding and fixing a pesky flow measurement problem in an Emerson Exchange presentation, THUM’S UP! : Wireless Troubleshooting of Intermittent Upsets.

The story was of a paper manufacturer with a remote wastewater area. The operators were seeing unacceptable flow variability. When they would ask the maintenance technicians to check out at the flow meter device, the technicians would find stable flow conditions. The team could not locate any obvious process or environmental conditions. Too much flow could lead to spillage and a possible Environmental Protection Agency (EPA) violation. Also, process critical inventory was required to keep pH and other process parameters where they needed to be.

The paper mill had multiple control systems as well as a mix of old and new instrumentation. The plant engineers were planning process improvements to improve overall mill performance. This intermittent troubleshooting kept the operators from focusing on value-creating activities, caused disruptions to the process during the troubleshooting process, and created tension among the plant staff.

Steve worked with the staff to review their options. These ranged from adding traditional diagnostic tools and local data acquisition to changing the I/O landing location of the flowmeter to a DCS from the current remote PLC. The third option was to add a Wireless THUM adapter to the magnetic flowmeter, activate the device diagnostics, and monitor these diagnostics remotely through the wireless network’s on-line AMS Device Manager. This third option was the path chosen.

The operators were able to see diagnostics associated with grounding faults, wiring faults, and high process noise from the magmeter. These conditions are often the culprits with intermittent readings. Any diagnostic alerts would also be saved into a device audit trail to see if any patterns emerged over time.

The project costs included a diagnostic upgrade to the magnetic flow transmitter, a THUM WirelessHART adapter, installation time and materials, adding the device to the existing wireless network, and activating monitoring in the AMS Device Manager. The project implementation time was two hours and the installation cost approximately $2000 USD.

The plant operations staff has not had a diagnostic alert since the work was performed earlier this year and the tensions between the operators and maintenance technicians over this troublesome issue have been alleviated. The focus has shifted back to finding other areas to improve mill performance.

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