If a Disconnected PLC Runs the Wrong Program in the Field and No One Notices, Does It Still Create a Problem?

Ahh, the proverbial tree falling in the proverbial woods question…can something exist without it being perceived? Does the same question apply to a water company’s disconnected automation assets out in the field if the utility doesn’t know that there is problem with the device? That question can be answered quickly with a definitive “yes.” The customer will discover the problem in the form of interrupted service.

Utility companies have challenges that other automation users may not face: disconnected devices at field sites many miles away from the plant, and continual changes to programmable devices due to growth, climate change, and community expectations. In a connected plant environment if a device fails, the engineer will find out quickly as people are present to observe the problem. A connected plant will still experience downtime and possibly product loss if they do not have a copy of the correct program readily available to load into the device. These problems are easily compounded in remote operations when discovery of the problem and getting to the site can be delayed.

Both connected and disconnected operations need a good Change Management System (CMS) to provide backup and recovery of program data in the event of device failures and the ability to compare the program running on the device to the latest revision. For a CMS to be useful for many utilities, it must be also be suitable for the specialized operational demands in the field. For instance, disconnected devices should be supported by a checkout and check-in procedure, or better yet, non-networked tools can be used to download copies of programs from a central repository to provide the controls engineer access to the programs remotely. It is also helpful if the CMS can compare the program on the device with the one downloaded from the repository, capture user comments regarding program changes, assist in creating new programs in the field, and synchronize all changes back to repository.

Just as trees will always fall, automation device programs will always be changed. To ensure consistent process optimization and efficiency, uninterrupted service to customers, and staff safety, control system changes must be managed not only in connected plant environments but also at dispersed field sites.