C. Linearities

Regulatory references:
P75 Appendix A, § 3.2 and 6.2, Appendix B 2.2.1, and P75 Policy Manual Section # 9 (Span, Calibration and Linearity).

Pre-linearity Activities:

  1. Linearities need to be separated by at least 30 calendar days, if possible.
  2. Linearities are required for a unit after it has operated in at least 168 clock hours in a calendar quarter.
  3. If you did not perform a linearity in a quarter, you will have 168 operating hour grace period available in the next calendar quarter.
  4. Verify that you have the correct blend of gas cylinders needed to perform a linearity check.
  5. Verify that you have enough gas in each cylinder to allow you to perform 6-7 runs (several runs for troubleshooting and then three good runs for the actual linearity).
  6. Prepare for the linearity check itself by selecting the date for performing it and schedule it for that date with the various parties involved (your boss, the operating staff, etc.).
  7. Assemble whatever other supplies you need to perform the linearity check. This might include, but it is not limited to:
    1. Linearity check list or an in-house procedure.
    2. Whatever notes you need to use to perform a linearity.

Day of Linearity Activities:

  1. Review your in-house linearity procedure making sure you understand it and can answer questions from those whom you will work or interface with.
  2. Confirm with the other parties involved that the linearity can proceed today and that the unit is scheduled to operate long enough to complete the linearity.
  3. The linearity should only be performed after successfully completing the daily calibration check.
  4. When you are ready to begin, contact the control room operator and tell them you are beginning and ask if you can have steady operating conditions until you are done. Make them aware that they may see the CEMs reading jumping around as you perform the linearity.
  5. A successful linearity is completed by running three different sets of blended gases through the system three separate times. Each set of gases will have a low, mid and high concentration gas to it, and the average linearity error calculated at each level is ≤ 5.0% (or is within the difference allowed for the alternate specification) to be a successful linearity audit. 
  6. Once you begin, and until the ninth run is recorded, no adjustments are allowed to the monitors. If any adjustment is necessary, then the linearity for that monitor is now aborted and the EPA considers an aborted linearity to be a failed linearity.
  7. Start each run of the three gases after the data system has recorded minute data in the first two clock quadrants. A properly executed linearity can be successfully completed in three hours, and still have valid hourly averages based on collecting two data points per hour during a QA check.
  8. When the linearity is over, review the system while you are still in the shelter and make sure it has been restored to normal operating status. Make sure the gas cylinders are set up and valved in for a successful calibration check in the next morning.

When you are done – Wrapping It Up:

  1. Take your notes from the linearity and setup your linearity records in the linearity editor of StackVision.  Make sure the editor says that you have “Passed”. Save the linearity records.
  2. Make a note of how much pressure remains in the cylinders for the next round of linearities.  If any cylinder has less than 500 psi, it’s time to verify that you have a replacement cylinder in hand.  If none are available, then order at least two more sets of cylinders.  Remember, it takes at least 28 days at the factory to blend up a Protocol I gas, as required by USEPA.
  3. Remember to associate or link the relevant gas cylinder certificates used in the linearities for the Part 75 gas monitors.  Linking these certificates for a CGA under P60 is not necessary.
  4. When you think the linearity records are completed, generate a QA file for the date that the linearity was performed on.  Import that EDR file into ECMPS and evaluate it. The evaluation report should report “No Errors”. If it reports anything errors, follow up appropriately in StackVision (SV) as needed.
  5. Remember that linearity records for SO2, NOx, CO2, or O2 are only to be included in QA EDR files. Do not check the box to “Include in the EDR file” for CO or any other type of systems.
  6. QA records for linearities can be submitted at any time, once they are deemed clean and ready. Submissions of QA records through ECMPS should only be made through the prior approval of the Designated Representative (DR) according to your plant’s submission procedures.
  7. A CGA (Cylinder Gas Audit) is not the same as a linearity. A CGA is performed with only two gas cylinders of different concentrations while a linearity requires three cylinders with concentrations within a specific range of the span of the system. For more details regarding CGAs, see the One Page Tips for P60. 
Downlaod the pdf document here.

Jon Konings, Senior Regulatory and Reporting Engineer, ESC    Published: 10/23/2016 5:10:39 PM

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