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Recently, I was asked to help a customer set up the Relative Accuracy Test Audit (RATA) records in StackVision™. The customer provided me with the tables summarizing the RATA run times and the average pollutant concentration values recorded by both the stack testers and the in-house Continuous Emissions Monitoring (CEM) system for each run. But when the results were entered into and evaluated in StackVision, the results showed the RATA failed.

After troubleshooting for several hours, we traced the problem back to the fact the data system used by the stack testers was not synchronized to the same time reference as StackVision (note that this problem could also have occurred with Prism™). The stack testers ignored the fact the data system used for a CEM system is required by Part 75 regulation to always record the time in standard time, and should not switch back and forth between daylight saving time and standard time. An accurate comparison of the performance of two emission monitoring systems cannot be achieved if the same reference time standard is not used (i.e. both systems need to be recording in standard time). Once corrected to bring the two sets of data into proper time alignment, the results were much better, and the RATA results were acceptable.

Before beginning a RATA, or any other emissions evaluation test, stack testers must synchronize their time reference to match the time reference used by their CEM system. They should be tracking “controller” as closely as possible so an accurate comparison of emission and operating data can be achieved.

Remember that the data system, as outlined in the Part 75 Policy Manual (Q & A 13.4), is required to continuously record its operating time in standard time. While not a requirement for CEM systems which are purely a Part 60 or 63 monitoring system, it is a commonly found practice. Some plants do switch back and forth between daylight saving time and standard time, and this makes comparing data between the CEM DAS and the plant DCS (Distributed Control System) difficult and confusing.

Be sure you understand how your CEM data system addresses the issue of daylight saving time. Your Quality Assurance Quality Control (QA/QC) plan should spell out that your data system always records in standard  time.

For questions, suggestions, or for a general chat, do not hesitate to contact me.


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Jon Konings

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