Directive 2005/55/EC of the European Parliament and of the Council (repealed)Show full title

Appendix 5 CALIBRATION PROCEDURE

1. CALIBRATION OF THE ANALYTICAL INSTRUMENTS U.K.

1.1. Introduction U.K.

Each analyser shall be calibrated as often as necessary to fulfil the accuracy requirements of this Directive. The calibration method that shall be used is described in this section for the analysers indicated in Annex III, Appendix 4, Section 3 and Annex V, Section 1.

1.2. Calibration gases U.K.

The shelf life of all calibration gases must be respected.

The expiration date of the calibration gases stated by the manufacturer shall be recorded.

1.2.1. Pure gases U.K.

The required purity of the gases is defined by the contamination limits given below. The following gases must be available for operation:

• Purified nitrogen

  (Contamination ≤ 1 ppm C1, ≤ 1 ppm CO, ≤ 400 ppm CO₂, ≤ 0,1 ppm NO)

• Purified oxygen

  (Purity > 99,5 % vol O₂)

• Hydrogen-helium mixture

  (40 ± 2 % hydrogen, balance helium)

  (Contamination ≤ 1 ppm C1, ≤ 400 ppm CO₂)

• Purified synthetic air

  (Contamination ≤ 1 ppm C1, ≤ 1 ppm CO, ≤ 400 ppm CO₂, ≤ 0,1 ppm NO)

  (Oxygen content between 18-21 % vol.)

• Purified propane or CO for the CVS verification

1.2.2. Calibration and span gases U.K.

Mixtures of gases having the following chemical compositions shall be available:

C₃H₈ and purified synthetic air (see Section 1.2.1);

CO and purified nitrogen;

NO_x and purified nitrogen (the amount of NO₂ contained in this calibration gas must not exceed 5 % of the NO content);

CO₂ and purified nitrogen;

CH₄ and purified synthetic air;

C₂H₆ and purified synthetic air.

Note: Other gas combinations are allowed provided the gases do not react with one another. U.K.

The true concentration of a calibration and span gas must be within ± 2 % of the nominal value. All concentrations of calibration gas shall be given on a volume basis (volume percent or volume ppm).

The gases used for calibration and span may also be obtained by means of a gas divider, diluting with purified N₂ or with purified synthetic air. The accuracy of the mixing device must be such that the concentration of the diluted calibration gases may be determined to within ± 2 %.

1.3. Operating procedure for analysers and sampling system U.K.

The operating procedure for analysers shall follow the start-up and operating instructions of the instrument manufacturer. The minimum requirements given in Sections 1.4 to 1.9 shall be included.

1.4. Leakage test U.K.

A system leakage test shall be performed. The probe shall be disconnected from the exhaust system and the end plugged. The analyser pump shall be switched on. After an initial stabilisation period all flow meters should read zero. If not, the sampling lines shall be checked and the fault corrected.

The maximum allowable leakage rate on the vacuum side shall be 0,5 % of the in-use flow rate for the portion of the system being checked. The analyser flows and bypass flows may be used to estimate the in-use flow rates.

Another method is the introduction of a concentration step change at the beginning of the sampling line by switching from zero to span gas. If after an adequate period of time the reading shows a lower concentration compared to the introduced concentration, this points to calibration or leakage problems.

1.5. Calibration procedure U.K.

1.5.1. Instrument assembly U.K.

The instrument assembly shall be calibrated and calibration curves checked against standard gases. The same gas flow rates shall be used as when sampling exhaust.

1.5.2. Warming-up time U.K.

The warming-up time should be according to the recommendations of the manufacturer. If not specified, a minimum of two hours is recommended for warming up the analysers.

1.5.3. NDIR and HFID analyser U.K.

The NDIR analyser shall be tuned, as necessary, and the combustion flame of the HFID analyser shall be optimised (Section 1.8.1).

1.5.4. Calibration U.K.

Each normally used operating range shall be calibrated.

Using purified synthetic air (or nitrogen), the CO, CO₂, NO_x and HC analysers shall be set at zero.

The appropriate calibration gases shall be introduced to the analysers, the values recorded, and the calibration curve established according to Section 1.5.5.

The zero setting shall be rechecked and the calibration procedure repeated, if necessary.

1.5.5. Establishment of the calibration curve U.K.

1.5.5.1. General guidelines U.K.

The analyser calibration curve shall be established by at least five calibration points (excluding zero) spaced as uniformly as possible. The highest nominal concentration must be equal to or higher than 90 % of full scale.

The calibration curve shall be calculated by the method of least squares. If the resulting polynomial degree is greater than 3, the number of calibration points (zero included) must be at least equal to this polynomial degree plus 2.

The calibration curve must not differ by more than ± 2 % from the nominal value of each calibration point and by more than ± 1 % of full scale at zero.

From the calibration curve and the calibration points, it is possible to verify that the calibration has been carried out correctly. The different characteristic parameters of the analyser must be indicated, particularly:

• the measuring range,

• the sensitivity,

• the date of carrying out the calibration.

1.5.5.2. Calibration below 15 % of full scale U.K.

The analyser calibration curve shall be established by at least 4 additional calibration points (excluding zero) spaced nominally equally below 15 % of full scale.

The calibration curve is calculated by the method of least squares.

The calibration curve must not differ by more than ± 4 % from the nominal value of each calibration point and by more than ± 1 % of full scale at zero.

1.5.5.3. Alternative methods U.K.

If it can be shown that alternative technology (e.g. computer, electronically controlled range switch, etc.) can give equivalent accuracy, then these alternatives may be used.

1.6. Verification of the calibration U.K.

Each normally used operating range shall be checked prior to each analysis in accordance with the following procedure.

The calibration shall be checked by using a zero gas and a span gas whose nominal value is more than 80 % of full scale of the measuring range.

If, for the two points considered, the value found does not differ by more than ± 4 % of full scale from the declared reference value, the adjustment parameters may be modified. Should this not be the case, a new calibration curve shall be established in accordance with Section 1.5.5.

1.7. Efficiency test of the NO_x converter U.K.

The efficiency of the converter used for the conversion of NO₂ into NO shall be tested as given in Sections 1.7.1 to 1.7.8 (Figure 6).

1.7.1. Test set-up U.K.

Using the test set-up as shown in Figure 6 (see also Annex III, Appendix 4, Section 3.3.5) and the procedure below, the efficiency of converters can be tested by means of an ozonator.

1.7.2. Calibration U.K.

The CLD and the HCLD shall be calibrated in the most common operating range following the manufacturer's specifications using zero and span gas (the NO content of which must amount to about 80 % of the operating range and the NO₂ concentration of the gas mixture to less than 5 % of the NO concentration). The NO_x analyser must be in the NO mode so that the span gas does not pass through the converter. The indicated concentration has to be recorded.

1.7.3. Calculation U.K.

The efficiency of the NO_x converter is calculated as follows:

where,

a

=

is the NO_x concentration according to Section 1.7.6

b

=

is the NO_x concentration according to Section 1.7.7

c

=

is the NO concentration according to Section 1.7.4

d

=

is the NO concentration according to Section 1.7.5

1.7.4. Adding of oxygen U.K.

Via a T-fitting, oxygen or zero air is added continuously to the gas flow until the concentration indicated is about 20 % less than the indicated calibration concentration given in Section 1.7.2. (The analyser is in the NO mode). The indicated concentration c shall be recorded. The ozonator is kept deactivated throughout the process.

1.7.5. Activation of the ozonator U.K.

The ozonator is now activated to generate enough ozone to bring the NO concentration down to about 20 % (minimum 10 %) of the calibration concentration given in Section 1.7.2. The indicated concentration d shall be recorded. (The analyser is in the NO mode).

1.7.6. NO_x mode U.K.

The NO analyser is then switched to the NO_x mode so that the gas mixture (consisting of NO, NO₂, O₂ and N₂) now passes through the converter. The indicated concentration a shall be recorded. (The analyser is in the NO_x mode).

1.7.7. Deactivation of the ozonator U.K.

The ozonator is now deactivated. The mixture of gases described in Section 1.7.6 passes through the converter into the detector. The indicated concentration b shall be recorded. (The analyser is in the NO_x mode).

1.7.8. NO mode U.K.

Switched to NO mode with the ozonator deactivated, the flow of oxygen or synthetic air is also shut off. The NO_x reading of the analyser shall not deviate by more than ± 5 % from the value measured according to Section 1.7.2. (The analyser is in the NO mode).

1.7.9. Test interval U.K.

The efficiency of the converter must be tested prior to each calibration of the NO_x analyser.

1.7.10. Efficiency requirement U.K.

The efficiency of the converter shall not be less than 90 %, but a higher efficiency of 95 % is strongly recommended.

Note: If, with the analyser in the most common range, the ozonator cannot give a reduction from 80 % to 20 % according to Section 1.7.5, then the highest range which will give the reduction shall be used. U.K.

1.8. Adjustment of the FID U.K.

1.8.1. Optimisation of the detector response U.K.

The FID must be adjusted as specified by the instrument manufacturer. A propane in air span gas should be used to optimise the response on the most common operating range.

With the fuel and air flow rates set at the manufacturer's recommendations, a 350 ± 75 ppm C span gas shall be introduced to the analyser. The response at a given fuel flow shall be determined from the difference between the span gas response and the zero gas response. The fuel flow shall be incrementally adjusted above and below the manufacturer's specification. The span and zero response at these fuel flows shall be recorded. The difference between the span and zero response shall be plotted and the fuel flow adjusted to the rich side of the curve.

1.8.2. Hydrocarbon response factors U.K.

The analyser shall be calibrated using propane in air and purified synthetic air, according to Section 1.5.

Response factors shall be determined when introducing an analyser into service and after major service intervals. The response factor (R_f) for a particular hydrocarbon species is the ratio of the FID C1 reading to the gas concentration in the cylinder expressed by ppm C1.

The concentration of the test gas must be at a level to give a response of approximately 80 % of full scale. The concentration must be known to an accuracy of ± 2 % in reference to a gravimetric standard expressed in volume. In addition, the gas cylinder must be preconditioned for 24 hours at a temperature of 298 K ± 5 K (25 °C ± 5 °C).

The test gases to be used and the recommended relative response factor ranges are as follows:

methane and purified synthetic air 1,00 ≤ R_f ≤ 1,15

propylene and purified synthetic air 0,90 ≤ R_f ≤ 1,10

toluene and purified synthetic air 0,90 ≤ R_f ≤ 1,10

These values are relative to the response factor (R_f) of 1,00 for propane and purified synthetic air.

1.8.3. Oxygen interference check U.K.

The oxygen interference check shall be determined when introducing an analyser into service and after major service intervals.

The response factor is defined and shall be determined as described in Section 1.8.2. The test gas to be used and the recommended relative response factor range are as follows:

This value is relative to the response factor (R_f) of 1,00 for propane and purified synthetic air.

The FID burner air oxygen concentration must be within ± 1 mole % of the oxygen concentration of the burner air used in the latest oxygen interference check. If the difference is greater, the oxygen interference must be checked and the analyser adjusted, if necessary.

1.8.4. Efficiency of the non-methane cutter (NMC, for NG fuelled gas engines only) U.K.

The NMC is used for the removal of the non-methane hydrocarbons from the sample gas by oxidising all hydrocarbons except methane. Ideally, the conversion for methane is 0 %, and for the other hydrocarbons represented by ethane is 100 %. For the accurate measurement of NMHC, the two efficiencies shall be determined and used for the calculation of the NMHC emission mass flow rate (see Annex III, Appendix 2, Section 4.3).

1.8.4.1. Methane efficiency U.K.

Methane calibration gas shall be flown through the FID with and without bypassing the NMC and the two concentrations recorded. The efficiency shall be determined as follows:

where,

conc_w

=

HC concentration with CH₄ flowing through the NMC

conc_w/o

=

HC concentration with CH₄ bypassing the NMC

1.8.4.2. Ethane efficiency U.K.

Ethane calibration gas shall be flown through the FID with and without bypassing the NMC and the two concentrations recorded. The efficiency shall be determined as follows

where,

conc_w

=

HC concentration with C₂H₆ flowing through the NMC

conc_w/o

=

HC concentration with C₂H₆ bypassing the NMC

1.9. Interference effects with CO, CO₂, and NO_x analysers U.K.

Gases present in the exhaust other than the one being analysed can interfere with the reading in several ways. Positive interference occurs in NDIR instruments where the interfering gas gives the same effect as the gas being measured, but to a lesser degree. Negative interference occurs in NDIR instruments by the interfering gas broadening the absorption band of the measured gas, and in CLD instruments by the interfering gas quenching the radiation. The interference checks in Sections 1.9.1 and 1.9.2 shall be performed prior to an analyser's initial use and after major service intervals.

1.9.1. CO analyser interference check U.K.

Water and CO₂ can interfere with the CO analyser performance. Therefore, a CO₂ span gas having a concentration of 80 to 100 % of full scale of the maximum operating range used during testing shall be bubbled through water at room temperature and the analyser response recorded. The analyser response must not be more than 1 % of full scale for ranges equal to or above 300 ppm or more than 3 ppm for ranges below 300 ppm.

1.9.2. NO_x analyser quench checks U.K.

The two gases of concern for CLD (and HCLD) analysers are CO₂ and water vapour. Quench responses to these gases are proportional to their concentrations, and therefore require test techniques to determine the quench at the highest expected concentrations experienced during testing.

1.9.2.1. CO₂ quench check U.K.

A CO₂ span gas having a concentration of 80 to 100 % of full scale of the maximum operating range shall be passed through the NDIR analyser and the CO₂ value recorded as A. It shall then be diluted approximately 50 % with NO span gas and passed through the NDIR and (H)CLD, with the CO₂ and NO values recorded as B and C, respectively. The CO₂ shall then be shut off and only the NO span gas be passed through the (H)CLD and the NO value recorded as D.

The quench, which must not be greater than 3 % of full scale, shall be calculated as follows:

where,

A

=

is the undiluted CO₂ concentration measured with NDIR in %

B

=

is the diluted CO₂ concentration measured with NDIR in %

C

=

is the diluted NO concentration measured with (H)CLD in ppm

D

=

is the undiluted NO concentration measured with (H)CLD in ppm

Alternative methods of diluting and quantifying of CO₂ and NO span gas values such as dynamic mixing/blending can be used.

1.9.2.2. Water quench check U.K.

This check applies to wet gas concentration measurements only. Calculation of water quench must consider dilution of the NO span gas with water vapour and scaling of water vapour concentration of the mixture to that expected during testing.

A NO span gas having a concentration of 80 to 100 % of full scale of the normal operating range shall be passed through the (H)CLD and the NO value recorded as D. The NO span gas shall then be bubbled through water at room temperature and passed through the (H)CLD and the NO value recorded as C. The analyser's absolute operating pressure and the water temperature shall be determined and recorded as E and F, respectively. The mixture's saturation vapour pressure that corresponds to the bubbler water temperature F shall be determined and recorded as G. The water vapour concentration (H, in %) of the mixture shall be calculated as follows:

The expected diluted NO span gas (in water vapour) concentration (D_e) shall be calculated as follows:

For diesel exhaust, the maximum exhaust water vapour concentration (H_m, in %) expected during testing shall be estimated, under the assumption of a fuel atom H/C ratio of 1,8:1, from the undiluted CO₂ span gas concentration (A, as measured in Section 1.9.2.1) as follows:

The water quench, which must not be greater than 3 %, shall be calculated as follows:

where,

D_e

=

is the expected diluted NO concentration in ppm

C

=

is the diluted NO concentration in ppm

H_m

=

is the maximum water vapour concentration in %

H

=

is the actual water vapour concentration in %

Note: It is important that the NO span gas contains minimal NO₂ concentration for this check, since absorption of NO₂ in water has not been accounted for in the quench calculations. U.K.

1.10. Calibration intervals U.K.

The analysers shall be calibrated according to Section 1.5 at least every three months or whenever a system repair or change is made that could influence calibration.

2. CALIBRATION OF THE CVS-SYSTEM U.K.

2.1. General U.K.

The CVS system shall be calibrated by using an accurate flowmeter traceable to national or international standards and a restricting device. The flow through the system shall be measured at different restriction settings, and the control parameters of the system shall be measured and related to the flow.

Various types of flowmeters may be used, e.g. calibrated venturi, calibrated laminar flowmeter, calibrated turbinemeter.

2.2. Calibration of the Positive Displacement Pump (PDP) U.K.

All parameters related to the pump shall be simultaneously measured with the parameters related to the flowmeter which is connected in series with the pump. The calculated flow rate (in m³/min at pump inlet, absolute pressure and temperature) shall be plotted versus a correlation function which is the value of a specific combination of pump parameters. The linear equation which relates the pump flow and the correlation function shall then be determined. If a CVS has a multiple speed drive, the calibration shall be performed for each range used. Temperature stability shall be maintained during calibration.

2.2.1. Data analysis U.K.

The air flowrate (Q_s) at each restriction setting (minimum six settings) shall be calculated in standard m³/min from the flowmeter data using the manufacturer's prescribed method. The air flow rate shall then be converted to pump flow (V₀) in m³/rev at absolute pump inlet temperature and pressure as follows:

where,

Q_s

=

air flow rate at standard conditions (101,3 kPa, 273 K), m³/s

T

=

temperature at pump inlet, K

p_A

=

absolute pressure at pump inlet (p_B-p₁), kPa

n

=

pump speed, rev/s

To account for the interaction of pressure variations at the pump and the pump slip rate, the correlation function (X₀) between pump speed, pressure differential from pump inlet to pump outlet and absolute pump outlet pressure shall be calculated as follows:

where,

Δp_p

=

pressure differential from pump inlet to pump outlet, kPa

p_A

=

absolute outlet pressure at pump outlet, kPa

A linear least-square fit shall be performed to generate the calibration equation as follows:

D₀ and m are the intercept and slope constants, respectively, describing the regression lines.

For a CVS system with multiple speeds, the calibration curves generated for the different pump flow ranges shall be approximately parallel, and the intercept values (D₀) shall increase as the pump flow range decreases.

The calculated values from the equation shall be within ± 0,5 % of the measured value of V₀. Values of m will vary from one pump to another. Particulate influx over time will cause the pump slip to decrease, as reflected by lower values for m. Therefore, calibration shall be performed at pump start-up, after major maintenance, and if the total system verification (Section 2.4) indicates a change of the slip rate.

2.3. Calibration of the Critical Flow Venturi (CFV) U.K.

Calibration of the CFV is based upon the flow equation for a critical venturi. Gas flow is a function of inlet pressure and temperature, as shown below:

where,

K_v

=

calibration coefficient

p_A

=

absolute pressure at venturi inlet, kPa

T

=

temperature at venturi inlet, K

2.3.1. Data analysis U.K.

The air flowrate (Q_s) at each restriction setting (minimum eight settings) shall be calculated in standard m³/min from the flowmeter data using the manufacturer's prescribed method. The calibration coefficient shall be calculated from the calibration data for each setting as follows:

where,

Q_s

=

air flow rate at standard conditions (101,3 kPa, 273 K), m³/s

T

=

temperature at the venturi inlet, K

p_A

=

absolute pressure at venturi inlet, kPa

To determine the range of critical flow, K_v shall be plotted as a function of venturi inlet pressure. For critical (choked) flow, K_v will have a relatively constant value. As pressure decreases (vacuum increases), the venturi becomes unchoked and K_v decreases, which indicates that the CFV is operated outside the permissible range.

For a minimum of eight points in the region of critical flow, the average K_v and the standard deviation shall be calculated. The standard deviation shall not exceed ± 0,3 % of the average K_V.

2.4. Total system verification U.K.

The total accuracy of the CVS sampling system and analytical system shall be determined by introducing a known mass of a pollutant gas into the system while it is being operated in the normal manner. The pollutant is analysed, and the mass calculated according to Annex III, Appendix 2, Section 4.3 except in the case of propane where a factor of 0,000472 is used in place of 0,000479 for HC. Either of the following two techniques shall be used.

2.4.1. Metering with a critical flow orifice U.K.

A known quantity of pure gas (carbon monoxide or propane) shall be fed into the CVS system through a calibrated critical orifice. If the inlet pressure is high enough, the flow rate, which is adjusted by means of the critical flow orifice, is independent of the orifice outlet pressure (≡ critical flow). The CVS system shall be operated as in a normal exhaust emission test for about 5 to 10 minutes. A gas sample shall be analysed with the usual equipment (sampling bag or integrating method), and the mass of the gas calculated. The mass so determined shall be within ± 3 % of the known mass of the gas injected.

2.4.2. Metering by means of a gravimetric technique U.K.

The weight of a small cylinder filled with carbon monoxide or propane shall be determined with a precision of ± 0,01 gram. For about 5 to 10 minutes, the CVS system shall be operated as in a normal exhaust emission test, while carbon monoxide or propane is injected into the system. The quantity of pure gas discharged shall be determined by means of differential weighing. A gas sample shall be analysed with the usual equipment (sampling bag or integrating method), and the mass of the gas calculated. The mass so determined shall be within ± 3 % of the known mass of the gas injected.

3. CALIBRATION OF THE PARTICULATE MEASURING SYSTEM U.K.

3.1. Introduction U.K.

Each component shall be calibrated as often as necessary to fulfil the accuracy requirements of this Directive. The calibration method to be used is described in this section for the components indicated in Annex III, Appendix 4, Section 4 and Annex V, Section 2.

3.2. Flow measurement U.K.

The calibration of gas flow meters or flow measurement instrumentation shall be traceable to international and/or national standards. The maximum error of the measured value shall be within ± 2 % of reading.

If the gas flow is determined by differential flow measurement, the maximum error of the difference shall be such that the accuracy of G_EDF is within ± 4 % (see also Annex V, Section 2.2.1, EGA). It can be calculated by taking the Root-Mean-Square of the errors of each instrument.

3.3. Checking the partial flow conditions U.K.

The range of the exhaust gas velocity and the pressure oscillations shall be checked and adjusted according to the requirements of Annex V, Section 2.2.1, EP, if applicable.

3.4. Calibration intervals U.K.

The flow measurement instrumentation shall be calibrated at least every three months or whenever a system repair or change is made that could influence calibration.

4. CALIBRATION OF THE SMOKE MEASUREMENT EQUIPMENT U.K.

4.1. Introduction U.K.

The opacimeter shall be calibrated as often as necessary to fulfil the accuracy requirements of this Directive. The calibration method to be used is described in this section for the components indicated in Annex III, Appendix 4, Section 5 and Annex V, Section 3.

4.2. Calibration procedure U.K.

4.2.1. Warming-up time U.K.

The opacimeter shall be warmed up and stabilised according to the manufacturer's recommendations. If the opacimeter is equipped with a purge air system to prevent sooting of the instrument optics, this system should also be activated and adjusted according to the manufacturer's recommendations.

4.2.2. Establishment of the linearity response U.K.

The linearity of the opacimeter shall be checked in the opacity readout mode as per the manufacturer's recommendations. Three neutral density filters of known transmittance, which shall meet the requirements of Annex III, Appendix 4, Section 5.2.5, shall be introduced to the opacimeter and the value recorded. The neutral density filters shall have nominal opacities of approximately 10 %, 20 % and 40 %.

The linearity must not differ by more than ± 2 % opacity from the nominal value of the neutral density filter. Any non-linearity exceeding the above value must be corrected prior to the test.

4.3. Calibration intervals U.K.

The opacimeter shall be calibrated according to Section 4.2.2 at least every three months or whenever a system repair or change is made that could influence calibration.