📏 Quality assurance of AMS — QAL2 calibration, QAL3 control and the annual AST test

Metrology PN-EN 14181

Overview

EN 14181 describes the quality assurance procedures needed to demonstrate that an automated measuring system (AMS) installed to measure emissions to air meets the requirements for the uncertainty of the measured values arising from the law (EU directives, national provisions) or from the competent authorities. Three levels of quality assurance are defined: QAL1 — the suitability of the AMS for the task (in accordance with EN 15267-3 and EN ISO 14956, with a calculation of the total uncertainty from the performance characteristics), QAL2 — validation after installation, QAL3 — control during operation, and the annual surveillance test (AST). The standard specifies: the QAL2 procedure for calibrating the AMS and determining the variability of the measured values, in order to demonstrate the suitability of the AMS after installation; the QAL3 procedure for maintaining and demonstrating the quality of the results in normal operation by checking the agreement of the zero and span characteristics with those established in QAL1; the AST procedure assessing whether the AMS is working correctly and whether the calibration function and the variability remain valid. It is applied after the certification of the AMS in accordance with the EN 15267 series; the QAL2 and AST procedures are carried out by testing laboratories, QAL3 — by the operator of the plant. The 2014 edition replaced EN 14181:2004. In Poland the regulation on the measurement of the quantity of emissions requires that continuous measurement systems be subject to procedures in accordance with PN-EN 14181, including at least once a year a control by parallel measurements with the reference methods (dust, SO₂, NOx, CO, O₂, water vapour), the full calibration and validation procedure for new systems, for existing ones at least once every five years and after major changes, and that the confidence intervals of a single result be determined in accordance with that standard.

Method principle

The AMS must have had its suitability for the task (the parameter and the composition of the gas) demonstrated in QAL1 — new plants require certification in accordance with EN 15267-1, -2, -3; EN 15267-3 requires the total uncertainty from the test to be at least 25 % below the maximum permissible one, in order to leave a margin for the influence of the installation. QAL2: on a correctly installed and commissioned AMS a series of parallel measurements is carried out with the standard reference method (SRM) in the same sampling plane; from the pairs of results a linear calibration function is determined (for dust a quadratic one is permissible in accordance with EN 13284-2) as well as the variability — the standard deviation of the differences between the SRM and the calibrated AMS — and it is compared by a test with the maximum permissible uncertainty (σ₀ derived from the provisions, e.g. σ₀ = P·E/1.96, where the uncertainty is given as half of the 95 % confidence interval as a percentage P of the permissible value E). QAL2 is repeated periodically, after a major change in the operation of the plant, after a failure of the AMS or where the law requires it. QAL3: periodic checks of the zero and the span with reference materials (as in the repeatability tests of QAL1) and assessment of the results with CUSUM or EWMA control charts against the uncertainty components from QAL1; where necessary, adjustment or servicing. AST: functional tests and a limited number of parallel SRM measurements checking whether the uncertainty and the calibration function from the previous QAL2 still hold. The standard does not cover the uncertainty of the data acquisition and handling system (DAHS); it distinguishes the certification range (≤ 1.5 × the daily ELV for incineration plants, ≤ 2.5 × for large combustion plants), the calibration range and the measuring range.

Applications

• Calibration and validation (QAL2) of continuous emission monitoring systems for SO₂, NOx, CO, dust, O₂, H₂O, HCl, NH₃, Hg and others after installation
• Annual control (AST) and five-yearly full calibration of continuous measurement systems required by the regulation on measurements of emissions
• Ongoing control by the operator (QAL3) — control charts of the drift and the precision at zero and at span
• Determination of the confidence intervals of a single result of a continuous measurement for comparison with the emission standards
• Assessment of existing, non-certified AMS (annex H.2) and of peripheral systems (temperature, pressure, O₂, water vapour)

Key parameters

Standard

Standard number

PN-EN 14181:2015-02 (EN 14181:2014)

Title (PL)

Emisja ze źródeł stacjonarnych — Zapewnienie jakości automatycznych systemów pomiarowych

Title (EN)

Stationary source emissions — Quality assurance of automated measuring systems

Step-by-step procedure

1. QAL1 — suitability

   Make sure that the AMS is certified in accordance with EN 15267-1/-2/-3 for the parameter and the composition of the gas and that its total uncertainty from QAL1 meets the requirements of the provisions with a margin of 25 %; for existing non-certified systems apply annex H.2.

2. QAL2 — parallel measurements

   After installation and commissioning have a laboratory carry out a series of parallel SRM measurements (in the same sampling plane, under conditions covering the operating range of the plant) with simultaneous recording of the AMS signal, after a functional check of the AMS.

3. QAL2 — calibration function and variability

   From the pairs (xi, yi) determine the calibration function (the best estimates of a and b), calculate the differences Di and their standard deviation sD, carry out the variability test against σ₀; establish the calibration range (ys,min – ys,max). A non-compliant result → corrective actions and repetition.

4. QAL3 — ongoing control

   The operator periodically (at intervals no longer than the maintenance interval) checks the zero and the span with reference materials, plots the results on CUSUM or EWMA charts and compares them with the limits from QAL1; on an exceedance — adjustment or maintenance.

5. AST — annual test

   Each year the laboratory carries out functional tests of the AMS and a limited number of parallel SRM measurements; it checks whether the variability is within the criteria and whether the calibration function from QAL2 remains valid; in the event of non-compliance — a new QAL2.

6. Repetition of QAL2 and documentation

   Repeat QAL2 periodically (in Poland at least once every 5 years), after a major change in the operation of the plant, after a failure or a repair of the AMS; document the calibration function, the variability, the confidence intervals of a single result and all the tests.

Required equipment and apparatus

Health and safety (OHS)

• Parallel SRM measurements on a stack platform — protection against falling, hot ports, toxic gases
• Test gases for the checks of zero and span (NO, CO, SO₂) — secured cylinders, ventilation, venting of the outlets

Frequently asked questions