SMART Data: Preventing data gaps with intelligent PLCs

smartDATAWe recently encountered an interesting challenge when one of our clients needed to ensure that all of their information is being gathered and stored by their SCADA system in the event of a data collection interruption. With a diverse assortment of reporting sites and technologies currently in use, the customer needed a fix that is both reliable for today and into the future. In the end Eramosa Engineering created a robust solution that allows the system to collect and backfill data to a historian during a communication outage without data loss.

Our client is part of the water industry where it is paramount that data be collected and stored by a SCADA system at rates governed by regulatory agencies. These organisations ensure that all water quality compliance reporting is done accurately. Otherwise, the operating authority can be subject to fines and other major consequences if there is an incident affecting public safety. Thus, there is a need to capture all data while the system is producing treated water.

The client operates dozens of water treatment and distribution sites including both surface and ground water sources. These systems have both in-plant and remote PLCs in outstations. They also require a mix of hardwired and wireless (long haul) connections – often at lower speeds and with less reliability.

This disparity in systems can often mean there are outages from factors like extreme weather, construction, human error or technical problems such as telecom glitches. SCADA systems without hardwired connections to the data collector of the historian, or without store-and-forward data logging in the remote PLC, means data gaps will occur in communication outage.

Working with our client we created a fairly simple Add-On-Instruction for the PLC that samples instrument data at a specified rate. It locally stores time stamp, quality and data values for any number of analog values in the PLC program. Depending on the hardware and version of the CPU, the PLC can hold sufficient amounts of data to span most major communication outages.

On the SCADA server side we were able to develop a very elegant data harvester to intelligently collect and backfill data from the PLC data array.  Data is collected using an index tracking system and any information collected by the PLC is inserted into the SQL database. It can be immediately queried using a SCADA, reporting or other corporate system that can access SQL records. In the case of our client we were able to leverage their existing e.RIS web based reporting system to surface the data for reporting and data analysis.

The end result is that our client no longer has to worry about communication outages or problems with server side processes that disrupt data collection. Interruptions can last for days but all of the logged data will begin to be uploaded within the first minute of being back online.

For more information please contact Clinton.Tonge@eramosa.com.

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