Valid calibration interval

Unfortunately, it is a major task for plant owners to report whether the plant’s AMS measurements are within the valid calibration interval cf. MEL 16 from ref-lab and EN 14181:2014 (E) 6.5.

Save yourself the hassle and let ReportLoq do the documentation for you.

Your mean values (STA) must comply with the calibration interval of the QAL2 report if your installation uses QAL2. The aim is to ensure that the AMS measurements of the plant are a maximum of 10% outside the calibration range used during QAL2. For example, if NOx has a calibration range of 0-450 mg/nm3, STA values above 495 mg/nm3 would be recorded as being outside the range.

The QAL2 report therefore shows a calibration interval which must be entered in ReportLoq. It is then automatically checked for compliance with the calibration interval as described in MEL-16 and EN 14181 (E).

You can read more about the rules for calibration intervals in MEL-16. In section 10.1 point 5 it is described that:

  1. More than 5% of SSTA values* are outside the valid calibration interval for more than 5 weeks in the period between two AST or AST and QAL 2, or
  2. More than 40% of SSTA values* are outside the valid calibration interval for one week.

ReportLoq provides the following tools to report compliance with the calibration interval as specified in this rule.
*SSTA = Normalised hourly mean values without confidence interval subtraction

Report: QAL2 valid calibration interval

This report can be used as a support tool to document whether the installation has stayed within the calibration interval.

It contains a weekly inventory of:

  • the number of valid intervals measured during operation
  • a statement of the number of these that were more than 10% outside the valid calibration interval
  • a percentage weighting of overruns for the week

The report is produced on an annual basis and thus provides a good overview of a long period of AMS measurements.

Example of report

Specific exceedances

In order to demonstrate compliance with MEL-16 section 10.1 point 5a, it is necessary to take into account AST and QAL2 dates. If these are entered into ReportLoq, the automatic check will use this information to check for 5 weeks of AMS measurements with more than 5% measurements outside the calibration interval. In the case of such a situation, an overflow is generated in ReportLoq, which draws attention to the problem. 1 week with 40% is handled in the same way. This means that you will be actively alerted to the problem if you have not seen it in the report.

The exceedances “5 weeks of 5%” and “1 week of 40%” can be included in exceedance reports for e.g. immediate reporting.

168-hour rule (EN 14181:2014 6.5)

The standard requires that the last 168 hours of valid operation of the installation be used to calculate the exceedance rate

The separate exceedances actively seek to account for the last 168 hours of operation at the facility during the exceedance rate evaluation. The rule means in practice that previous weeks’ data may be used in the calculation, which means that the calibration report does not always show the correct percentage. However, ReportLoq takes into account the situation of the separate exceedances.

It is worth noting that ReportLoq does not penalize for the same period twice. Therefore, previous weeks with 5% or 40% exceedances will be sorted out before calculating the overrun percentage.

In brief

It is important that the AMS measurements are within the calibration ranges to be sure that the measurements are correct. Let ReportLoq do the check automatically by entering only the min and max calibration range when creating QAL2.

Then ReportLoq takes care of all the checks, so you can spend your time on other important tasks.


Do you already have ReportLoq but need the report, or are you just not sure how to interpret it? Or would you like to learn more about ReportLoq so you can decide if it’s right for you? Contact us for a no-obligation chat.

Share this post