Guidance

MCERTS: performance standards and test procedures for automatic isokinetic samplers

Updated 4 September 2025

Applies to England

This guidance describes the certification process and performance standards for automatic isokinetic samplers used to measure emissions from stacks.

1. Overview of MCERTS for automatic isokinetic samplers

Automatic isokinetic samplers are used within monitoring systems that measure pollutants, such as particulate matter, dioxins and furans, and mercury. These samplers are permanently installed equipment used for sampling over an extended time, for example 2 to 4 weeks.

MCERTS for automatic isokinetic samplers is an official certification scheme that complies with EN ISO/IEC 17065 Conformity assessment – Requirements for bodies certifying products, processes and services. The certification body appointed to run this scheme is CSA Group Testing UK Ltd.

You can find the requirements for certification and for the manufacturer’s quality management system for manufacturing and design control of monitoring systems in:

• EN 15267-1 Air quality - Certification of automatic measuring systems - Part 1: General aspects
• EN 15267-2 Air quality - Certification of automatic measuring systems - Part 2: Minimum requirements for product quality assurance, initial assessment and on-going surveillance

2. Introducing the performance criteria

The performance criteria that the standard specifies for automatic isokinetic samplers includes:

• general criteria for all automatic measuring systems
• performance criteria and test procedures for testing in a laboratory
• performance criteria and test procedures for field testing

Performance requirements are for system characteristics that relate to the isokinetic sampling of pollutants. Other components of the monitoring system and subsequent offline analysis stage of the collected pollutants is not included as this is outside the remit of the automatic isokinetic sampler.

3. Required standards

You will need the following standards for the testing of automatic isokinetic samplers:

• EN ISO 16911-1 – Stationary source emissions – Manual and automatic determination of velocity and volume flow rate in ducts Part 1: Manual reference method
• EN 15259 Air Quality – Measurement of stationary source emissions – Requirements for measurement sections and sites and for the measurement objective, plan and report

4. General requirements

The general requirements from the standards that are applicable to the certification of automatic isokinetic samplers are as follows. The Environment Agency provides additional requirements that are specific to automatic isokinetic samplers later in this guidance.

4.1 Application of performance requirements 

The test laboratory shall test at least 2 identical automatic isokinetic samplers. All samplers tested shall meet the performance criteria specified in this guidance as well as the requirement for the maximum permissible expanded uncertainty. 

4.2 Ranges to be tested

A minimum velocity range of 2 to 30 metres per second (m/s) shall be used. 

4.3 Certification ranges

A minimum certification range of 2 to 30 m/s shall be used.

4.4 Manufacturing consistency and design changes

Certification is specific to the automatic isokinetic sampler version that has undergone performance testing. Subsequent design modifications that might affect the performance of the automatic isokinetic sampler may invalidate the certification.

4.5 Qualification of test laboratories

Test laboratories shall have the competence for performing emission measurements and carrying out the tests defined in this guidance.

Test laboratories shall have the knowledge on the uncertainties attributed to the individual test procedures applied during the performance test. 

5. Performance criteria and test procedures for laboratory testing

This section describes the performance criteria for laboratory testing that are applicable to automatic isokinetic samplers from EN 15267-3 Air quality – Certification of automated measuring systems Part 3: Performance criteria and test procedures for automated measuring systems for monitoring emissions from stationary sources.

The test laboratory shall make sure that the sampler meets the criteria using the test procedures provided in EN 15267-3.

5.1 Automatic isokinetic sampler for testing

All automatic isokinetic samplers shall be complete, including the operation manual. The performance criteria apply to the complete sampler and not to the individual parts. The test report shall be issued for the specific sampler with all the main components. 

The design of the automatic isokinetic sampler should be compliant with the requirements of the relevant standards for the intended application (for example particulate matter, dioxins and furans, or mercury). This will allow integration of the automatic isokinetic sampler into a properly functioning system.

5.2 Evidence of compliance with legal requirements

Automatic isokinetic sampler manufacturers shall supply verifiable and traceable evidence of compliance with the requirements of the relevant product marking requirements for the intended market. This includes requirements on electromagnetic compatibility and voltage limits.

5.3 Security

The manufacturer shall make sure that the automatic isokinetic sampler shall have a means of protection against unauthorised access to control functions. 

5.4 Operational status signals

Automatic isokinetic samplers shall have a means of connecting an additional indicating and recording device.

Manufacturers shall make sure that automatic isokinetic samplers have a means of displaying their operating status.

The status signal covers:

• normal operation
• stand-by
• maintenance mode
• malfunction error signals

Automatic isokinetic samplers shall also have a means of communicating the operational status to the plant’s control system.

5.5 Degree of protection provided by enclosure 

Equipment protected from rain (they are in ventilated rooms or cabinets) shall meet at least IP40 as specified in EN 60529 Degrees of protection provided by enclosures (IP codes). 

Equipment located where some kind of shelter against precipitation is in place (for example a porch roof) but where rain can reach, shall meet at least IP54 as specified in EN 60529. 

Equipment designed for outdoor use in the open air and without weather protection shall at least meet the requirements of standard IP65 as specified in EN 60529. 

5.6 Influence of ambient temperature

The manufacturer shall make sure that the automatic isokinetic sampler is capable of operation from: 

• −20°C to +50°C for assemblies installed outdoors
• +5°C to +40°C for assemblies installed indoors, where the temperatures do not fall below +5°C or rise above +40°C

5.7 Influence of supply voltage variations 

The manufacturer shall make sure the automatic isokinetic sampler can operate at a supply voltage of −15% and +10%. 

6. Laboratory performance criteria and test procedures specific to automatic isokinetic samplers

Table 1 shows the performance criteria for automatic isokinetic samplers for different flow control performance characteristics.

Table 1: Performance criteria for automatic isokinetic samplers (laboratory tests using a wind tunnel)

Flow control performance characteristic	Performance criteria
Velocity range	2 to 30 m/s
Accuracy of isokinetic sampling rate response to changes in stack gas velocity	±5%
Accuracy of determination of volume of gas sampled	±2%
Linearity of isokinetic sampling rate	±5%
Response time, T90	<100 seconds
Flow repeatability under laboratory conditions	±5%
Minimum operational velocity	2 m/s
Drift (short term)	2%

Where the values for the performance requirements are expressed as a percentage, this is a percentage of the relevant reading.

You shall determine the reference values by using velocity measurement standards and then calculating the volume.

The following tests are in the same order they should be carried out in the laboratory.

6.1 Response (delay and rise) time

The delay time (T₁₀) is the time taken for the sampler to reach 10% of the expected response, following introduction of a step change in sampling velocity. 

The response time (T₉₀) is the time taken for equipment to reach 90% of the expected response, following introduction of the same step change.

The rise time is T₉₀ − T₁₀ .

The time shall be measured by introducing randomised step changes in the velocity at the input to the sampler. The size of each step shall be between 10% and 95% of the maximum of the certification range. The random sequence of steps will include both increased and decreased velocities and need not start from or end at zero.

6.2 Accuracy

The sampler shall be calibrated either in the factory or at the start of the laboratory tests using the manufacturer’s instructions.

Sampler calibration shall use the technique and any artefacts that are normally recommended by the manufacturer for this purpose. Any calibration artefacts used by the manufacturer shall be traceable to national standards. The test laboratory may comment on the calibration technique where appropriate.

The isokinetic sampling accuracy of the equipment, with the accuracy of the control of the volumetric sampling rate, shall be assessed using a wind tunnel when faced with different flue gas velocities.

You shall make this measurement using a reference instrument whose own calibration is traceable to national standards. You shall assess this at 2 velocities in the range of 2 to 30 m/s, for example 5 and 25 m/s.

6.3 Linearity

Linearity is the measure of fit of the automatic isokinetic sampler’s performance across its sampling range to a straight line, using a few approximately equally distributed values of the flow velocity and zero.

The linearity of the isokinetic response of the sampler to different flue gas velocities shall be tested over the full certification range of the instrument. Linearity testing shall use at least 5 velocity values approximately equally spaced across the range.

The measure of linearity is the maximum difference between any measured point and the regression line fit to all the points.

6.4 Drift (short term)

The isokinetic response of the sampler to a set gas velocity shall be observed over a 24-hour period to check for the presence of drift. The output values shall be averaged over periods of 4 instrument rise times, and these averaged values shall be compared to the value set at the beginning of the test.

The recorded drift of the equipment shall be taken as the difference between the value measured at the end of the test compared with the value at the beginning of the test.

6.5 Minimum operating (flue gas) velocity

The minimum operating flue gas velocity shall be determined by increasing the velocity of the sample, using a wind tunnel, from zero until the equipment responds with a performance within the specified linearity criteria.

You shall verify this minimum value by reducing the velocity of the sample from a higher velocity to the minimum value to ensure the equipment continues to respond correctly. You shall report this value.

6.6 Repeatability

The repeatability of the sampler is determined from the measured statistical variation of the isokinetic sampling rate response of the equipment when a set velocity is generated using a wind tunnel. The repeatability is defined as:

C_R = t_f(0.95).X_R

C_R is the repeatability expressed in velocity units.

X_R is the standard deviation of the measurements.

t_{f (0.95)} is the statistical Student t-factor for a 95% confidence level with f degrees of freedom.

Measurements shall be averaged over at least 4 times the response time of the equipment, and the standard deviation calculated.

The repeatability value determined by this test, expressed as a percentage of the maximum of the certification range, shall be less than the performance criteria value.

6.7 Suitability of construction material

You shall carry out a visual inspection of the equipment to ensure that the materials of construction are adequate for prolonged exposure to the flue gas environment expected.

If needed, the test laboratory may request details of construction materials from the manufacturer.

6.8 Monitoring of the sampling process

Any functions offered by the system to monitor the sampling process will be recorded in the test report, for example:

• software driven messages
• data readouts

7. Field testing performance criteria and test procedures

Table 2 shows the performance criteria and field test procedures of automatic isokinetic samplers installed at an industrial plant. Where applicable, the performance criteria and test procedures in EN 15267-3 shall be followed.

Table 2: Performance criteria for automatic isokinetic samplers (field tests)

Performance characteristic	Performance criteria
Accuracy of the determination of volume of gas sampled calculated as an average of 10 runs performed during the first or the last month of testing	±5%
Flow reproducibility under field conditions calculated from 10 independent measurement results at one fixed location within the duct	±5%
Availability over 3 months continuous use	>95%

7.1 General criteria

The field tests shall be done at a plant that is applicable for the intended application, such as:

• a municipal waste incinerator
• a co-incineration cement plant

The sample locations used during the field tests shall be in accordance with EN 15259.

7.2 Accuracy

The accuracy of the automatic isokinetic sampler is expressed in terms of the volume sampled. The accuracy of the volume sampled under field conditions shall be assessed using a reference method which shall meet the criteria set within EN ISO 16911-1.

Measurements with the automatic isokinetic sampler and a suitably located reference method shall be done during the first and third month of the field trial.

7.3 Instrument availability under field conditions

The overall availability of the sampler is defined as the fraction of the total monitoring time for which data and sample material of acceptable quality has been collected.

The overall availability of the sampler is recorded during the 3-month programme of site tests.

8. What to do next 

Find out more about MCERTS product certification on the: 

• CSA website
• MCERTS collection on GOV.UK

Contact the Environment Agency if you need any help.

General enquiries

National Customer Contact Centre
PO Box 544
Rotherham
S60 1BY

Email enquiries@environment-agency.gov.uk

Telephone 03708 506 506

Telephone from outside the UK (Monday to Friday, 8am to 6pm GMT) +44 (0) 114 282 5312

Monday to Friday, 8am to 6pm.