BS EN 14626-2012 pdf download.Ambient air Standard method for the measurement of the concentration of carbon monoxide by non-dispersive infrared spectroscopy.
This standard describes the method for measurement of the concentration of carbon monoxide in ambient air by means of non-dispersive infrared spectroscopy. The requirements, the specific components of the infrared analyser and its sampling system are described. A number of performance characteristics with associated minimum performance criteria are given for the analyser. The actual values of these performance characteristics for a specific type of analyser shall be determined in a so-called type approval test for which procedures have been described. The type approval test comprises a laboratory test and a field test, The selection of a type-approved analyser for a specific measuring task in the field is based on the calculation of the expanded uncertainty of the measurement method. In this expanded uncertainty calculation, the actual values of various performance characteristics of a type-approved analyser and the site-specific conditions at the monitoring station are taken into account (see 9.6). The expanded uncertainty of the method shall not exceed 15 % for fixed measurements or 25 % for indicative measurements, as specified in Annex I of Directive 2008150!EC [1]. Requirements and recommendations for quality assurance and quality control are given for the measurements in the field (see 9.4).
5.2 Measuring principle
The attenuation of infrared light passing through a sample cell is a measure of the concentration of CO in the cell, according to the Lambert-Beer law. Not only CO but also most hetero-atomic molecules will absorb infrared light: in particular water and CO2 have broad bands that can interfere with the measurement of CO. Different technical solutions have been developed to suppress cross-sensitivity, instability and drift in order to design continuous monitoring systems with acceptable properties. For instance:
— measuring IR absorption of a specific wavelength (4,7 pm foc CO);
— dual-cell monitors, using a reference cell filled with clean air (compensation for drift);
— gas-filter correlation, measuring” over a range of wavelengths.
Special attention shall be paid to infrared radiation absorbing gases such as water vapour, carbon dioxide, nitrous oxide and hydrocarbons.
The concentration of carbon monoxide is measured in volumeivolume units (if the analyser is calibrated using a volume/volume standard). The final results for reporting are expressed in mg/rn3 using standard conversion factors (see Clause 10).
5.3 Type approval test
The type approval test is based on the evaluation of performance characteristics determined under a prescribed series of tests, In this European Standard, test procedures are described for the determination of the actual values of the performance characteristics for at least two anatysers in a laboratory and the same anatysers in the field, operated in parallel in both cases. The type approval laboratory tests shall not include the sampling inlet, sampling system and external data acquisition system, but shall include analyser sampling line and filter. The type approval field test may include a sampling inlet and a sampling system. However, the influence of these components on the test results shall be minimised by proper maintenance.
A designated body shall perform these tests. The evaluation for type approval of an analyser is based on the calculation of the expanded uncertainty in the measuring result based on the numerical values of the tested performance characteristics and compared with a prescribed maximum uncertainty.
The type approval of an analyser and subsequent QA and QC procedures provide evidence that the defined requirements concerning data quality laid out in Annex I of Directive 2008/50/EC (1J can be satisfied.
Appropriate experimental evidence shall be provided by
— type approval tests performed under conditions of intended use of the specified method of measurement, and
— calculation of expanded uncertainty of results of measurement by reference to ENV 13005.
5.4 Field operation and quality control
Prior to the installation and operation of a type approved analyser at a monitoring station, an expanded uncertainty calculation shall be performed with the actual values of the performance, obtained during the type approval tests. and the site-specific conditions at that monitoring station. This calculation shall be used to demonstrate that the type-approved analyser meets the requirements for all applicable limit values under the actual conditions present at that specific monitoring station.
After the installation of the approved analyser at the monitoring station, its correct functioning shall be tested.
Requirements for quality assurance and quality control are given for the operation and maintenance of the sampling system. as well as for the analyser, to ensure that the uncertainty of subsequent measurement results obtained in the field is not compromised.
6 Sampling
6.1 General.BS EN 14626-2012 pdf download.