Work we can Perform
A distinction need to be made between calibration work (one off discrepancies, linearity, gas factor, conversion rate, sensitivity to an interfering factor) from tests which cannot be accredited for calibration (repeatability, limits, response time, effect of power supply variations, flowrates, pressure, temperature, humidity, vibration and so on).
The laboratory performs the following activities:
Calibration at 1 to 5 points on the scale (accredited on display).
– Linearity at 7 points on the scale including zero (accredited on the display and analogue output).
– Calibration curve and function (accredited on the display and analogue output).
– Repeatability (zero and scale point) at 20 points (test not accredited on analogue or digital output).
– Limits by graphical method (test not accredited on analogue or digital output).
– Gas factor for FID analyzers (test accredited on analogue or digital output).
– NO2 conversion rate for chemiluminescence (test accredited on analogue or digital output).
– Ethane penetration rate for FIDs with oxidation oven (methane only).
And on request
– Sensitivity to an interfering factor (test accredited on analogue or digital output).
– Response time (test not accredited on analogue or digital output).
The level of interfering factors can vary depending on the general standard or on specific standards (state which standard to follow in your request).
The certified reference materials are ternary at most (air matrix).
Certified reference materials and pure gases are diluted in nitrogen or in air.
The calibration range is published on the website www.cofrac.fr (accreditation range or technical appendix).
Better uncertainty on reference concentrations obtained
The accreditation scope is used to estimate the best absolute enlarged uncertainty knowing the full scale of the instrument to be calibrated.
For work performed under NF EN 15267-3, the absolute enlarged uncertainty of the dilution system must be better than 33% of the value of the maximum tolerated deviation.
This requirement cannot be satisfied for NO, NO2 and CH4 (see accreditation scope).
Standard NF EN 12619 considers total organic compounds which it defines by a triple response to a concentration of propane. The effect of this is to triple the calibration uncertainty.
When a calibration certificate is requested, the laboratory gives the one-off deviations (1 to 5 scale points) with the uncertainty due to accuracy and screen resolution, i.e. a curve and a calibration function (at least 6 scale points).
If a verification report is requested, the laboratory will make a statement on its compliance with specified requirements which the customer must send to the laboratory with his request.
Results are provided with or without accreditation.
NF EN 15267-3
The following concentration levels are performed for the linearity check:
0% – 70% – 40% – 0% – 60% – 10% – 30% – 90% – 0% of full scale after adjustment to 0% and 70%.
Point of scale for repeatability (20 consecutive points): 80% of full scale.
Concentration of interfering gases:
– O2: 3% vol. and 21% vol.
– CO: 300 mg/m3;
– CO2: 15% vol.;
– CH4: 50 mg/m3;
– N2O: 20 mg/m3 and 100 mg/m3 (fluidized bed combustion);
– NO: 300 mg/m3;
– NO2: 30 mg/m3;
– NH3: 20 mg/m3;
– SO2: 200 mg/m3 and 1000 mg/m3 (coal fired thermal power plants without desulfurization);
– HCl: 50 mg/m3 and 200 mg/m3 (coal fired power plants).
Operation which, under specified conditions, first of all establishes a relationship between the values and associated measurement uncertainties which are provided by the standards and the corresponding readings with the associated uncertainties, and then secondly uses this information to establish a relation to obtain a measurement result from a reading.
NOTE 1: A calibration can be expressed in the form of a notice, a calibration function, a calibration diagram, a calibration curve or a calibration table. In some cases it can consist of a corrective addition or multiplication to the reading with an associated measurement uncertainty.
NOTE 2: Do not confuse calibration with adjustment of a measuring system, often incorrectly called “self-calibration”, nor with a calibration check.
Source: VIM 2008
Provision of tangible proof that a given entity satisfies specified requirements.
EXAMPLE 1 Confirmation that a given reference material is indeed uniform as declared for the measuring procedure and value concerned for mass measurements up to 10 mg.
EXAMPLE 2 Confirmation that properties that relate to legal performance or requirements are satisfied by a measuring system.
EXAMPLE 3 Confirmation that a target uncertainty can be achieved.
NOTE 1 If necessary, measurement uncertainty should be taken into account.
NOTE 2 The entity may be, for example, a process, a measuring procedure, a material, a component or a measuring system.
NOTE 3 Specified requirements can be, for instance, a manufacturer’s specifications.
NOTE 4 The legal metrology check as defined in VIML and more generally under a compliance assessment consists of inspecting, marking and/or issuing a check certification for a measuring system.
NOTE 5 Do not confuse verification with calibration. A verification is not a validation.
NOTE 6 In chemistry, verification of the identity of an entity or an activity requires a description of the structure or properties of that entity or activity.
Source: VIM 2008
Accreditation of the laboratory in accordance with ISO 17025 provides proof of its technical capability in the field of gas analyzers. It also shows that it has an effective quality management system. The laboratory also complies with the principles of ISO 9001:2000. Work carried out under accreditation is described in the scope of the accreditation of the laboratory.
The results of calibration under accreditation are recorded using the SI system of units.
Unless you specify otherwise, the specified requirements are the specifications of the manufacturer of the instrument (to be enclosed with your request for older items of equipment).