Thursday, 27 June 2013 15:48


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A West Midlands dairy recently experienced a problem with a blender that threatened to cause a production stoppage and downtime costs of around £3000 an hour.

The blending plant was exhibiting some unexplained operation of the valves and showing various valve position feedback alarms. Downtime from any operational failure is never good news and a return to full production was critical.

Monitoring the system controlling the process didn’t reveal anything obviously wrong but the site engineers knew they had to get the problem resolved as soon as possible and put in a call to the Mitsubishi technical support hotline.

Mitsubishi Electric has a firm commitment to service and technical support, via its System Service Group, providing added value services including 24 hour telephone support and a full complement of authorised engineers to provide everything from routine service to emergency downtime mitigation. The System Service offering supports both current and past generation product lines, with authorised Service Agents providing local engineers at regional centres and key partners providing expert advice and on-the-ground repairs.

Mitsubishi can also offer service support for other vendor’s automation equipment, providing a “one stop shop” and peace of mind.

The Mitsubishi technical support line took the call, evaluated the problem and contacted Mitsubishi Electric’s Service Agent NISCAM. Service engineer Carl Chadwick received the call, contacted the customer and took as much detail as possible. Then set off on the 33 mile journey to the plant, knowing that time was of the essence.

Mitsubishi Electric products are extremely reliable and it is not uncommon to find examples of PLCs still in continuous operation after 20 or more years of service. So, finding nothing wrong with the PLC itself as expected, Carl singled out one of the troublesome valves and started a code trace of the valve control logic. It was found that there was a request to open the valve but no output to the open solenoid. The logic was checked against an earlier backup taken three months earlier during a routine health check as part of the customer’s “Mitsubishi 3 Diamond Service Contract” and key differences were found.

The site laptop was checked and found to have two version of the program saved. One was fully commented, looking very much like the original post-commissioning work and a second, later version.

Comparing these two programs with the one loaded in the PLC, Carl quickly identified differences surrounding the valve control logic. It then emerged that modifications had been made by one of the dairy’s site engineers the previous Friday as part of ongoing efforts to improve productivity. Carl’s suspicion was that the valve control modification had been implemented but with a very slight error. Carl noted the changes then re-loaded the program and after testing found that the valves were now operating correctly, with no positional errors shown. Carl stayed on site for a further 30 minutes whilst the process was started, to ensure all valves operated and the process sequence was stable. Finally, he saved the program as the latest version, and retained a copy for the Mitsubishi archive system.

This cautionary tale of course highlights the importance of effective program management, fully commented documentation and regular backups, as part of a customised Diamond Service Contract. The problem would have been difficult and time consuming to diagnose but for the fact that Carl already had an archived backup against which to compare the incorrect program running in the PLC.

Perhaps more importantly it demonstrates Mitsubishi Electric’s commitment to service and support. With downtime costing the Dairy an estimated £3000 per hour, Mitsubishi’s ability to provide local engineering support to expedite a return to normal functionality certainly helped to save the day.

Read 538 times Last modified on Tuesday, 18 March 2014 18:13