Guidance

MCERTS: performance standard for low risk plant monitors

Published 6 December 2022

Applies to England and Wales

1. Overview

This guidance describes the certification process for low risk plant monitors.

These systems are used to make continuous measurements in a variety of applications, such as:

• stack emissions monitoring for indicative purposes
• monitoring some plants that fall under the Medium Combustion Plant Directive
• monitoring some plants that fall under the specified generator regulations

Low risk plant monitors are not suitable for quantitative measurements to meet the requirements of the Industrial Emissions Directive (IED). More information on monitoring equipment that meets the monitoring requirements of the IED is given in MCERTS for stack emissions monitoring equipment at industrial installations.

MCERTS for low risk plant monitors is an official certification scheme that complies with EN ISO/IEC 17065 Conformity assessment – Requirements for bodies certifying products, processes and services.

CSA Group UK Limited is a certification body appointed to run this scheme for the Environment Agency.

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

2. Scope

This document specifies the performance characteristics and test procedures for low risk plant monitors. The determinands covered include, but are not restricted to:

• sulfur dioxide
• oxides of nitrogen
• carbon monoxide and carbon dioxide
• methane
• volatile organic compounds, expressed as total organic carbon
• oxygen
• water vapour

3. Testing and certification

The following standard is required for the testing of low risk plant monitors under MCERTS:

• 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

To get certification for a low risk plant monitor you must arrange for it to be tested. You can:

• use a laboratory acceptable to the certification body
• carry out your own testing, if the certification body agrees that your test facilities meet the applicable quality assurance requirements specified in EN 15267-1
• choose to use a combination of both external and your own testing

If you decide to carry out your own testing, you must describe your test facilities to the certification body. Include arrangements for quality assurance and quality control of testing. Indicate which tests you want to perform yourselves.

If you carry out your own testing, then the results of the tests will be subject to an assessment and supervision by the certification body. The assessment will examine the test methods, test results and traceability.

When applying for certification, you must list the determinands measured, ranges and intended process applications. The performance data from testing may indicate that the possible range for each determinand may be greater or less than your nominated range. As lower ranges indicate better performance, you may decide to have a lower range based on the test results.

You may have had some tests already performed. If so, then you must include any relevant test reports with the application for certification. When some or all testing has already been carried out, the certification body will decide if any more tests are required. They will agree with you whether they can be performed using your own test facilities or at an external test laboratory.

4. Unique identification

The low risk plant monitor must have a unique designation that clearly identifies the equipment as a certified model.

Any changes in the design that influences the performance of the monitor must be reflected in the unique designation of the monitor. For example, a monitor that has been modified must be given a new model designation or number to distinguish it clearly from previous models.

5. Repairs, maintenance and changes

Any spares or replacement parts for a certified low risk plant monitor must meet the same performance standards as the original parts. Operators and equipment suppliers may be required to provide evidence that the replacement parts meet the required performance standards of the original equipment.

Changes to certified monitors are allowable if you can prove that these design changes do not degrade the performance of the monitor below the MCERTS performance standards.

You must keep detailed records and drawings of all design changes to the monitor. You must have arrangements for design verification, inspection and testing to make sure that the monitor still meets the required performance standards.

The certification body will conduct assessments of the design changes to monitors to meet the requirements of product certification. You must tell the certification body of any changes that may have a significant effect on the performance of the monitor.

You may need to arrange more testing of the monitor if you:

• change its design
• extend its range of application

The extent of this renewed testing will depend upon the nature of the changes.

If there is evidence that a change has only limited effects on the performance of the monitor, then only a supporting test would be required.

In the case of changes to software, you must provide documentation to the certification body showing the:

• nature of the modification
• resultant effects on operation and functionality

The certification body will then decide if any more testing is required.

6. Previous performance tests

You may send existing test data for low risk plant monitors.

7. Certificate validity

MCERTS certificates are valid for 5 years.

8. General requirements

Low risk plant monitors must have an indicator to show the measured parameters and value.

Monitors must have an output of at least −5% to +105% of the certification range.

This is to provide for a living zero reading, which means that the instrument can indicate both positive and negative drift. This requirement does not apply to oxygen monitors which use zirconia sensors.

The monitor must be equipped with a security mechanism to prevent inadvertent and unauthorised alteration. Security mechanisms can include a key or security code programmed into the system before adjustments are permitted.

The sampling system must be constructed to prevent damage to the sensors and pump by particulate matter and liquids in the stack gas. This will be verified by inspection.

9. Performance characteristics and test methods

Performance characteristics for low risk monitors are shown in tables 1 and 2. The values for individual performance characteristics are expressed as a percentage of the certification range unless otherwise stated.

Monitors for measuring total organic carbon must meet the performance criteria specified in table 1 and table 2

The performance criteria for the effect of oxygen and the response factors specified in table 3 must also be applied.

Table 1: Performance characteristics for low risk plant monitors in laboratory tests

Note: For oxygen, the performance specifications are expressed as a percentage of volume concentration of oxygen.

Performance characteristic	Gases except oxygen	Oxygen	EN 15267-3 clause
Response time	≤ 200 seconds	≤ 200 seconds	10.9
Repeatability at zero point	≤ 5%	≤ 0.4%	10.10
Repeatability at span point	≤ 5%	≤ 0.4%	10.11
Lack-of-fit (linearity)	≤ 5%	≤ 0.4%	10.12
Influence of ambient temperature change from 20ºC within specified range at zero point	≤ 5%	≤ 0.8%	10.14
Influence of ambient temperature change from 20ºC within specified range at span point	≤ 5%	≤ 0.8%	10.14
Influence of sample gas pressure at span point, for a pressure change (∆p) of 3 kPa	≤ 5%	≤ 0.8%	10.15
Influence of sample gas flow on extractive monitors for a given specification by the manufacturer	≤ 5%	≤ 0.8%	10.16
Influence of voltage, at −15 % below and at +10 % above nominal supply voltage	≤ 5%	≤ 0.8%	10.17
Influence of vibration	≤ 5%	≤ 0.8%	10.18
Cross-sensitivity	≤ 5%	≤ 0.8%	10.19
Excursion of the measurement beam of in-situ monitors	≤ 5%	Not applicable	10.20
Converter efficiency for monitors measuring oxides of nitrogen	≥ 95%	Not applicable	10.21

Table 2: Performance characteristics for low risk plant monitors in field tests

Note: For oxygen, the performance specifications are expressed as a percentage of volume concentration of oxygen.

Performance characteristic	Gases except oxygen	Oxygen	EN 15267-3 clause
Determination coefficient of calibration function, R²	≥ 0.9	≥ 0.9	12.1
Response time	≤ 200 seconds	≤ 200 seconds	12.2
Lack-of-fit (linearity)	≤ 5%	≤ 0.4%	12.3
Minimum maintenance interval	8 days	8 days	12.4
Zero drift with maintenance interval	≤ 5%	≤ 0.8%	12.5
Span drift with maintenance interval	≤ 5%	≤ 0.8%	12.5
Availability	≥ 95%	≥ 98%	12.6
Reproducibility, Rf	≤ 5%	≤ 0.8%	12.7

Table 3: Performance characteristics for low risk plant monitors measuring total organic carbon in laboratory tests

Performance characteristic: determinand	Performance criteria: response factor range
Effect of oxygen	≤ 5%
Methane response factor range	0.9 to 1.2
Aliphatic hydrocarbons response factor range	0.9 to 1.1
Aromatic hydrocarbons response factor range	0.8 to 1.1
Dichloromethane response factor range	0.75 to 1.15
Aliphatic alcohols response factor range	0.7 to 1
Esters and ketones response factor range	0.7 to 1
Organic acids response factor range	0.5 to 1

10. Test methods for low risk plant monitors

Response time

The test must be carried out in line with the requirements of EN 15267-3, Clause 10.9.

Repeatability at zero point

The test must be carried out in line with the requirements of EN 15267-3, Clause 10.10. The repeatability standard deviation at zero point must be calculated based on at least 5 consecutive individual readings.

Repeatability at span point

The test must be carried out in line with the requirements of EN 15267-3, Clause 10.11. The repeatability standard deviation at span point must be calculated based on at least 5 consecutive individual readings.

Lack-of-fit (linearity)

The test must be carried out in line with the requirements of EN 15267-3, Clause 10.12.

Influence of ambient temperature

The test must be carried out in line with the requirements of EN 15267-3, Clause 10.14. The ambient temperature range is usually −20°C to +50°C. The manufacturer may specify a different ambient temperature range. The ambient temperature range will be listed on the certificate.

Influence of sample gas pressure

The test must be carried out in line with the requirements of EN 15267-3, Clause 10.15.

Influence of sample gas flow for extractive monitors

The test must be carried out in line with the requirements of EN 15267-3, Clause 10.16.

Influence of voltage variations

The test must be carried out in line with the requirements of EN 15267-3, Clause 10.17.

Influence of vibration

The test must be carried out in line with the requirements of EN 15267-3, Clause 10.18.

Cross-sensitivity

The test must be carried out in line with the requirements of EN 15267-3, Clause 10.19. You must agree appropriate interferents with the certification body. The sum total of positive deviations and the sum total of negative deviations must be specified individually identifying the actual magnitude.

When determining cross-sensitivity of low risk plant monitors, the concentrations of interferents in table 4 must be used. The concentrations may need to be changed depending on the measuring technique, the type of system involved and the intended application. The interferents must be admitted individually.

Table 4: Recommended minimum concentrations of interferents

Interferent	Concentration	Unit
Oxygen	3 and 21	%
Water vapour	30	%
Carbon monoxide	300	mg/m³
Carbon dioxide	15	%
Methane	50	mg/m³
Nitrous oxide	20	mg/m³
Nitrogen monoxide	300	mg/m³
Nitrogen dioxide	30	mg/m³
Ammonia	20	mg/m³
Sulfur dioxide	200	mg/m³

Excursion of measurement beam of cross-stack in-situ monitors

The test must be carried out in line with the requirements of EN 15267-3, Clause 10.20.

Converter efficiency for oxides of nitrogen monitor

The test must be carried out in line with the requirements of EN 15267-3, Clause 10.21.

Response factors

The test must be carried out in line with the requirements of EN 15267-3, Clause 10.22.

13. Manufacturer’s quality system

You must have a quality system in place that complies with the requirements of ISO 9001 and the additional requirements of EN 15267-2.

You must have an annual assessment managed by the certification body. The assessment will not assess the elements covered by ISO 9001 certification. It will cover the additional requirements of EN 15267-2.

The assessment will include an evaluation of the arrangements for:

• the management and control of the design change process
• manufacturing (process control), final inspection tests and calibration to ensure reproducibility
• unambiguous identification of MCERTS certified equipment
• assuring that design changes do not degrade instrument performance such that instruments no longer meet the MCERTS performance standards

You must tell the certification body of any design changes to the low risk plant monitor. The certification body will then decide if the current certificate is still valid.

14. What to do next

Find out more about MCERTS product certification on the:

• CSA website
• MCERTS collection on GOV.UK

You can 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.