ASTM D6216-20

Standard Practice for Opacity Monitor Manufacturers to Certify Conformance with Design and Performance Specifications

SIGNIFICANCE AND USE
5.1 Continuous opacity monitors are required to be installed at many stationary sources of air pollution by federal, state, and local air pollution control agency regulations. EPA regulations regarding the design and performance of opacity monitoring systems for sources subject to “Standards of Performance for New Stationary Sources” are found in 40 CFR 60, Subpart A General Provisions, §60.13 Monitoring Provisions, Appendix B, Performance Specification 1, and in applicable source-specific subparts. Many states have adopted these or very similar requirements for opacity monitoring systems.  
5.2 Regulated industrial facilities are required to report continuous opacity monitoring data to control agencies on a periodic basis. The control agencies use the data as an indirect measure of particulate emission levels and as an indicator of the adequacy of process and control equipment operation and maintenance practices.  
5.3 EPA Performance Specification 1 provides minimum specifications for opacity monitors and requires source owners or operators of regulated facilities to demonstrate that their installed systems meet certain design and performance specifications. Performance Specification 1 adopts this ASTM practice by reference so that manufacturers can demonstrate conformance with certain design specifications by selecting and testing representative instruments.  
5.4 Experience demonstrated that EPA Performance Specification 1 prior to the Aug. 10, 2000 revisions did not address all of the important design and performance parameters for opacity monitoring systems. The additional design and performance specifications included in this practice are needed to eliminate many of the performance problems that were previously encountered. This practice also provides purchasers and vendors flexibility, by designing the test procedures for basic transmissometer components or opacity monitors, or in certain cases, complete opacity monitoring systems. However, the specificat...
SCOPE
1.1 This practice covers the procedure for certifying continuous opacity monitors. In the main part of this practice, it includes design and performance specifications, test procedures, and quality assurance requirements to ensure that continuous opacity monitors meet minimum design and calibration requirements, necessary in part, for accurate opacity monitoring measurements in regulatory environmental opacity monitoring applications subject to 10 % or higher opacity standards. In Annex A1, additional or alternative specifications are provided for certifying opacity monitors intended for use in applications where the opacity standard is less than 10 %, or where the user expects the opacity to be less than 10 % and elects to use the more restrictive criteria in Annex A1. In both cases, the error budgets for the opacity measurements are given in Appendix X1.  
1.2 This practice applies specifically to the original manufacturer, or to those involved in the repair, remanufacture, or resale of opacity monitors.  
1.3 Test procedures that specifically apply to the various equipment configurations of component equipment that comprise either a transmissometer, an opacity monitor, or complete opacity monitoring system are detailed in this practice.  
1.4 The specifications and test procedures contained in the main part of this practice have been adopted by reference by the United States Environmental Protection Agency (U.S. EPA). For each opacity monitor or monitoring system that the manufacturer demonstrates conformance to this practice, the manufacturer may issue a certificate that states that opacity monitor or monitoring system conforms with all of the applicable design and performance requirements of 40 CFR 60, Appendix B, Performance Specification 1 except those for which tests are required after installation.  
1.5 This international standard was developed in accordance with internationally recognized principles on sta...

General Information

• Status: Published
• Publication Date: 31-Aug-2020
• ICS: 17.180.30 - Optical measuring instruments
• Technical Committee: D22 - Air Quality
• Drafting Committee: D22.03 - Ambient Atmospheres and Source Emissions

Relations

• Refers: ASTM D1356-20a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Sep-2020
• Refers: ASTM D1356-20 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Mar-2020
• Refers: ASTM D1356-15a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Oct-2015
• Refers: ASTM D1356-15 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Jul-2015
• Refers: ASTM D1356-14b - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Dec-2014
• Refers: ASTM D1356-14a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-May-2014
• Refers: ASTM D1356-14 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Jan-2014
• Refers: ASTM D1356-05(2010) - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Apr-2010
• Refers: ASTM D1356-05 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-May-2005
• Refers: ASTM D1356-00a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 10-Nov-2000

Overview

ASTM D6216-20 is the Standard Practice developed by ASTM International for manufacturers of continuous opacity monitors (COMs) to certify that their equipment meets established design and performance specifications. These monitors are crucial for environmental regulatory compliance, as they provide continuous measurement of opacity in emissions from stationary sources, serving as an indirect indicator of particulate emissions and the effectiveness of air pollution control equipment.

This standard outlines rigorous requirements, detailed test procedures, and quality assurance protocols that ensure manufacturers can demonstrate conformance with U.S. Environmental Protection Agency (EPA) regulations, particularly 40 CFR 60, Appendix B, Performance Specification 1. Adoption of ASTM D6216-20 by manufacturers, users, and regulatory bodies plays a critical role in air quality management and regulatory reporting.

Key Topics

• Certifying Opacity Monitors: The standard specifies procedures for certifying COMs, including transmissometers and complete opacity monitoring systems, ensuring their suitability for regulatory applications.
• Design and Performance Specifications: Includes requirements for spectral response, angle of projection and view, supply voltage insensitivity, thermal stability, ambient light immunity, and calibration functionality.
• Test Procedures: Details the frequency and protocols for conducting design and performance tests both at the manufacturing stage and, optionally, after system repairs or remanufacture.
• Quality Assurance (QA): Stipulates the need for a robust QA program, corrective actions upon non-conformance, and proper documentation for traceability and audit purposes.
• Conformance and Certificates: Manufacturers can issue certificates demonstrating conformance with EPA specifications, adding value and credibility to their products in the marketplace.
• Flexible Testing Options: Provides flexibility in testing either component transmissometers, individual opacity monitors, or complete monitoring systems, as well as alternative or supplemental requirements for low-opacity applications.
• International Compliance: Developed to be consistent with international principles, supporting global harmonization and regulatory acceptance.

Applications

ASTM D6216-20 is widely used in various industries that must monitor and control air pollutants, especially:

• Industrial Facilities: Power plants, cement factories, refineries, and manufacturing plants utilize continuous opacity monitors to comply with emission limits set by environmental agencies.
• Regulatory Compliance: Facility operators use certified monitors to generate data for required periodic reporting to local, state, and federal air quality agencies.
• Instrumentation Manufacturing: Original manufacturers, as well as those engaged in equipment repair and remanufacture, apply this standard to ensure their products meet regulatory and performance expectations.
• Third-Party Auditing: The standard serves as a benchmark for independent audits and laboratory testing, supporting procurement, QA programs, and environmental due diligence.
• Low-Opacity Applications: Annexes provide procedures for equipment used in processes with opacity standards of less than 10%, accommodating stringent or specialized monitoring requirements.

Related Standards

Adhering to ASTM D6216-20 often requires consideration of related and referenced standards for a comprehensive compliance program:

• EPA 40 CFR 60, Appendix B, Performance Specification 1: Federal standard for opacity monitoring required at regulated stationary sources.
• ASTM D1356: Terminology relating to sampling and analysis of atmospheres.
• ANSI/NCSL Z 540-1-1994: General requirements for calibration laboratories and measuring equipment.
• ISO 9004: Guidelines for quality management and quality system elements.
• NIST 260-116: Procedures for filter calibration.
• ISO 842: Quality vocabulary.

Practical Value

Implementing ASTM D6216-20 ensures that continuous opacity monitors are reliable, accurate, and compliant with regulatory demands. This translates into:

• Regulatory Assurance: Streamlined approvals from environmental agencies.
• Operational Reliability: Reduced risk of non-compliance penalties.
• Market Advantage: Enhanced credibility for manufacturers and suppliers.
• Consistent Data Quality: Confidence in reported opacity and emission data.

By following ASTM D6216-20, industries and agencies support robust environmental monitoring and help drive continuous improvement in air quality management.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation:D6216 −20
Standard Practice for
Opacity Monitor Manufacturers to Certify Conformance with
Design and Performance Specifications
This standard is issued under the fixed designation D6216; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This practice covers the procedure for certifying con-
mendations issued by the World Trade Organization Technical
tinuous opacity monitors. In the main part of this practice, it
Barriers to Trade (TBT) Committee.
includes design and performance specifications, test
procedures, and quality assurance requirements to ensure that
2. Referenced Documents
continuous opacity monitors meet minimum design and cali-
2.1 ASTM Standards:
bration requirements, necessary in part, for accurate opacity
D1356 Terminology Relating to Sampling and Analysis of
monitoring measurements in regulatory environmental opacity
Atmospheres
monitoring applications subject to 10 % or higher opacity
2.2 U.S. Environmental Protection Agency Documents:
standards. In AnnexA1, additional or alternative specifications
40 CFR 60 Appendix B, Performance Specification 1
areprovidedforcertifyingopacitymonitorsintendedforusein
40 CFR 60 Appendix F, Procedure 3
applications where the opacity standard is less than 10 %, or
2.3 Other Documents:
where the user expects the opacity to be less than 10 % and
ANSI/NCSL Z 540-1-1994 Calibration Laboratories and
elects to use the more restrictive criteria in AnnexA1. In both
Measuring Equipment – General Requirements
cases,theerrorbudgetsfortheopacitymeasurementsaregiven
ISO 842 Quality Vocabulary
in Appendix X1.
ISO/DIS 9004 Quality Management and Quality System
1.2 This practice applies specifically to the original
Elements – Guidelines
manufacturer,ortothoseinvolvedintherepair,remanufacture,
NIST 260-116 Filter Calibration Procedures
or resale of opacity monitors.
3. Terminology
1.3 Test procedures that specifically apply to the various
3.1 Definitions—For terminology relevant to this practice,
equipment configurations of component equipment that com-
see Terminology D1356.
prise either a transmissometer, an opacity monitor, or complete
opacity monitoring system are detailed in this practice.
3.2 Definitions of Terms Specific to This Standard:
1.4 The specifications and test procedures contained in the
Analyzer Equipment
main part of this practice have been adopted by reference by
3.2.1 opacity, n—a measure of the degree to which the
the United States Environmental Protection Agency (U.S.
intensity of light is reduced as it passes through a gas, due to
EPA). For each opacity monitor or monitoring system that the
absorption and scattering.
manufacturer demonstrates conformance to this practice, the
3.2.1.1 Discussion—The degree to which the view of an
manufacturer may issue a certificate that states that opacity
object against the background is obscured increases with
monitor or monitoring system conforms with all of the appli-
increasing opacity. Opacity (Op) is related to transmittance (T)
cable design and performance requirements of 40 CFR 60,
through the equation:
Appendix B, Performance Specification 1 except those for
which tests are required after installation.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
1.5 This international standard was developed in accor-
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
dance with internationally recognized principles on standard- Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Available from U.S. Government Printing Office, Superintendent of
This practice is under the jurisdiction ofASTM Committee D22 on Air Quality Documents, 732 N. Capitol St., NW, Washington, DC 20401-0001, http://
and is the direct responsibility of Subcommittee D22.03 on Ambient Atmospheres www.access.gpo.gov.
and Source Emissions. Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
Current edition approved Sept. 1, 2020. Published September 2020. Originally 4th Floor, New York, NY 10036, http://www.ansi.org.
approved in 1998. Last previous edition approved in 2012 as D6216 – 12. Available from National Institute of Standards and Technology (NIST), 100
DOI:10.1520/D6216-20. Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6216−20
Op 5 1 2T (1) 3.2.6 transmittance, n—the fraction of incident light within
a specified optical region that passes through an optical
3.2.2 opacity monitor, n—an instrument that continuously
medium.
determines the opacity of emissions released to the atmo-
sphere. 3.2.7 transmissometer, n—an instrument that passes light
throughaparticulate-ladeneffluentstreamandmeasures in situ
3.2.2.1 Discussion—An opacity monitor includes a trans-
the optical transmittance of that light within a specified
missometer that determines the in-situ opacity, a means to
wavelength region.
correctopacitymeasurementstoequivalentsingle-passopacity
3.2.7.1 Discussion—Single-pass transmissometers consist
valuesthatwouldbeobservedatthepathlengthoftheemission
ofalightsourceanddetectorcomponentsmountedonopposite
outlet, and all other interface and peripheral equipment neces-
endsofthemeasurementpath.Double-passinstrumentsconsist
sary for continuous operation.
of a transceiver (including both light source and detector
3.2.2.2 Discussion—An opacity monitor may include the
components) and a reflector mounted on opposite ends of the
following: (1) sample interface equipment such as filters and
measurement path.
purge air blowers to protect the instrument and minimize
3.2.7.2 Discussion—For the purposes of this practice, the
contamination of exposed optical surfaces, (2) shutters or other
transmissometer includes the following mechanisms (1) means
devices to provide protection during power outages or failure
to verify the optical alignment of the components and (2)
of the sample interface, and (3) a remote control unit to
simulated zero and upscale calibration devices to check cali-
facilitate monitoring the output of the instrument, initiation of
bration drifts when the instrument is installed on a stack or
zero and upscale calibration checks, or control of other opacity
duct.
monitor functions.
3.2.7.3 Discussion—Transmissometers are sometimes re-
3.2.3 opacity monitor model, n—a specific transmissometer
ferred to as opacity analyzers when they are configured to
or opacity monitor configuration identified by the specific
measure opacity.
measurement system design, including: (1) the use of specific
light source, detector(s), lenses, mirrors, and other optical
Analyzer Zero Adjustments and Devices
components, (2) the physical arrangement of optical and other
3.2.8 dust compensation, n—a method or procedure for
principal components, (3) the specific electronics configuration
systematically adjusting the output of a transmissometer to
and signal processing approach, (4) the specific calibration
account for reduction in transmitted light reaching the detector
check mechanisms and drift/dust compensation devices and
(apparent increase in opacity) that is specifically due to the
approaches, and (5) the specific software version and data
accumulation of dust (that is, particulate matter) on the
processing algorithms, as implemented in a particular manu-
exposed optical surfaces of the transmissometer.
facturing process, at a particular facility and subject to an
3.2.8.1 Discussion—Dust compensation may be included as
identifiable quality assurance system.
an optional feature but is not required.
3.2.3.1 Discussion—Changingtheretro-reflectormaterialor
3.2.8.2 Discussion—The dust compensation is determined
the size of the retro-reflector aperture is not considered to be a
relative to the previous occasion when the exposed optics were
model change unless it changes the basic attributes of the
cleaned and the dust compensation was reset to zero. The
optical system.
determination of dust accumulation on surfaces exposed to the
3.2.3.2 Discussion—Minor changes to software or data
effluent must be limited to only those surfaces through which
outputsmaynotbeconsideredasamodelchangeprovidedthat
the light beam passes under normal opacity measurement and
the manufacturer documents all such changes and provides a
the simulated zero device or equivalent mechanism necessary
satisfactory explanation in a report.
for the dust compensation measurement. The determination of
3.2.4 opacity monitoring system, n—the entire set of equip- dust compensation is not required to include all surfaces
ment necessary to monitor continuously the in-stack opacity, exposed to the effluent or dust accumulation.
average the emission measurement data, and permanently
3.2.8.3 Discussion—The dust accumulation for all of the
record monitoring results.
optical surfaces included in the dust compensation method
must actually be measured. Unlike zero drift, which may be
3.2.4.1 Discussion—An opacity monitoring system includes
at least one opacity monitor with all of its associated interface either positive or negative, dust compensation can only reduce
the apparent opacity. A dust compensation procedure can
and peripheral equipment and the specific data recording
system (including software) employed by the end user. An correct for specific bias and provide measurement results
opacity monitoring system may include multiple opacity moni- equivalent to the clean window condition.
tors and a common data acquisition and recording system.
3.2.8.4 Discussion—In those cases where dust compensa-
tion is used, the opacity monitor must provide a means to
3.2.5 optical density (OD), n—a logarithmic measure of the
display the level of dust compensation. Regulatory require-
amount of incident light attenuated.
ments may impose a limit on the amount of dust compensation
3.2.5.1 Discussion—OD is related to transmittance and
that can be applied and require that an alarm be activated when
opacity as follows:
the limit is reached.
OD 5 log 1/T 52log T 52log 1 2 Op (2)
~ ! ~ ! ~ !
10 10 10
3.2.9 external audit device, n—an external device for simu-
where Op is expressed as a fraction. lating the zero opacity condition during a calibration error test.
D6216−20
3.2.10 external zero device, n—an external device for transmissometer, particulate matter (that is, dust) deposited on
checking the zero alignment of the transmissometer by simu- optical surfaces may contribute to zero drift. Zero drift may be
lating the zero opacity condition for a specific installed opacity positive or negative.
monitor.
Calibrations and Adjustments
3.2.10.1 Discussion—The external zero device can also be
3.2.15 attenuator, n—a glass or grid filter that reduces the
used as an external audit device provided it meets the require-
transmittance of light.
ments of both.
3.2.16 calibration drift, n—the difference between the opac-
3.2.11 simulated zero device, n—an automated mechanism
ity monitor response to the upscale calibration device and its
withinthetransmissometerthatproducesasimulatedclearpath
nominal value after a period of normal continuous operation
condition or low level opacity condition.
during which no maintenance, repairs, or external adjustments
3.2.11.1 Discussion—The simulated zero device is used to
to the opacity monitor took place.
check zero drift daily or more frequently and whenever
3.2.16.1 Discussion—Calibration drift may be determined
necessary (for example, after corrective actions or repairs) to
after determining and correcting for zero drift. For opacity
assess opacity monitor performance while the instrument is
monitors that include automatic zero compensation or dust
installed on the stack or duct.
compensation features, calibration drift may be determined
3.2.11.2 Discussion—The proper response to the simulated
after zero drift or dust compensation, or both, are applied.
zero device is established under clear path conditions while the
transmissometer is optically aligned at the installation path- 3.2.17 calibration error, n—thesumoftheabsolutevalueof
length and accurately calibrated. The simulated zero device is the mean difference and confidence coefficient for the opacity
then the surrogate, clear path calibration value, while the values indicated by an optically aligned opacity monitor
opacity monitor is in service. (laboratory test) or opacity monitoring system (field test) as
compared to the known values of three calibration attenuators
3.2.11.3 Discussion—Simulated zero checks do not neces-
sarily assess the optical alignment, the reflector status (for under clear path conditions.
double-pass systems), or the dust contamination level on all 3.2.17.1 Discussion—The calibration error indicates the
optical surfaces. (See also 6.9.1.) fundamental calibration status of the opacity.
3.2.12 zero alignment, n—the process of establishing the 3.2.18 external adjustment, n—either (1) a physical adjust-
quantitativerelationshipbetweenthesimulatedzerodeviceand ment to a component of the opacity monitoring system that
the actual clear path opacity responses of a transmissometer. affects its response or its performance, or (2) an adjustment
applied by the data acquisition system (for example, math-
3.2.13 zero compensation, n—an automatic adjustment of
ematical adjustment to compensate for drift) which is external
the transmissometer to achieve the correct response to the
to the transmissometer and control unit, if applicable.
simulated zero device.
3.2.18.1 Discussion—External adjustments are made at the
3.2.13.1 Discussion—The zero compensation adjustment is
election of the end user but may be subject to various
fundamental to the transmissometer design and may be inher-
regulatory requirements.
ent to its operation (for example, continuous adjustment based
oncomparisontoreferencevalues/conditions,useofautomatic 3.2.19 intrinsic adjustment, n—an automatic and essential
control mechanisms, rapid comparisons with simulated zero feature of an opacity monitor that provides for the internal
and upscale calibration drift check values, and so forth) or it control of specific components or adjustment of the opacity
may occur each time a calibration check cycle (zero and monitor response in a manner consistent with the manufactur-
upscalecalibrationdriftcheck)isperformedbyapplyingeither er’s design of the instrument and its intended operation.
analog or digital adjustments within the transmissometer.
3.2.19.1 Discussion—Examples of intrinsic adjustments in-
3.2.13.2 Discussion—For opacity monitors that do not dis- clude automatic gain control used to maintain signal ampli-
tinguish between zero compensation and dust compensation, tudes constant with respect to some reference value, or the
the accumulated zero compensation may be designated as the technique of ratioing the measurement and reference beams in
dust compensation. Regulatory requirements may impose a dual beam systems. Intrinsic adjustments are either non-
limit on the amount of dust compensation that can be applied elective or are configured in accordance with factory recom-
and require that an alarm be activated when the limit is mended procedures; they are not subject to change from time
reached. to time at the discretion of the end user.
3.2.14 zero drift, n—the difference between the opacity 3.2.20 upscale calibration device, n—an automated mecha-
monitor response to the simulated zero device and its nominal nism (employing a filter or reduced reflectance device) within
value (reported as percent opacity) after a period of normal the transmissometer that produces an upscale opacity value.
continuous operation during which no maintenance, repairs, or 3.2.20.1 Discussion—The upscale calibration device is used
external adjustments to the opacity monitor took place.
tochecktheupscaledriftofthemeasurementsystem.Itmaybe
3.2.14.1 Discussion—Zero drift may occur due to changes used in conjunction with the simulated zero device (for
in the light source, changes in the detector, variations due to example, filter superimposed on simulated zero reflector) or a
internal scattering, changes in electronic components, or vary- parallel fashion (for example, zero and upscale (reduced
ing environmental conditions such as temperature, voltage or reflectance) devices applied to the light beam sequentially).
other external factors. Depending on the design of the (See also 6.9.2.)
D6216−20
Opacity Monitor Location Characteristics 3.2.30 peak spectral response, n—the wavelength of maxi-
mum sensitivity of the transmissometer.
3.2.21 installation pathlength, n—the installation flange-to-
flangeseparationdistancebetweenthetransceiverandreflector 3.2.31 photopic, n—a region of the electromagnetic spec-
for a double-pass transmissometer or between the transmitter trumdefinedbytheresponseofthelight-adaptedhumaneyeas
and receiver for a single-pass transmissometer. characterized in the “Source C, Human Eye Response” con-
tained in 40 CFR 60, Appendix B, Performance Specification
3.2.22 monitoring pathlength, n—the effective single pass
1.
depth of effluent between the receiver and the transmitter of a
single-pass transmissometer, or between the transceiver and
4. Summary of Practice
reflector of a double-pass transmissometer at the installation
location.
4.1 A comprehensive series of specifications and test pro-
cedures that opacity monitor manufacturers must use to certify
3.2.23 emission outlet pathlength, n—the physical path-
opacity monitoring equipment (that is, that the equipment
length (single pass depth of effluent) at the location where
meetsminimumdesignandperformancerequirements)priorto
emissions are released to the atmosphere.
shipment to the end user is provided. The design and perfor-
3.2.23.1 Discussion—For circular stacks, the emission out-
mance specifications are summarized in Table 1.
let pathlength is the internal diameter at the stack exit. For
non-circular outlets, the emission outlet pathlength is the 4.2 Design specifications and test procedures for (1) peak
hydraulic diameter. For rectangular stacks: and mean spectral responses, (2) angle of view and angle of
projection, (3) insensitivity to supply voltage variations, (4)
D 5 2LW / L1W (3)
~ ! ~ !
thermal stability, (5) insensitivity to ambient light, and (6)an
where L is the length of the outlet and W is the width
optional procedure for opacity monitors with external zero
of the stack exit.
devices which regulatory agencies may require are included.
The manufacturer periodically selects and tests for confor-
3.2.24 pathlength correction factor (PLCF), n—the ratio of
mance with these design specifications an instrument that is
the emission outlet pathlength to the monitoring pathlength.
representative of a group of instruments) produced during a
3.2.24.1 Discussion—The PLCF is used to calculate the
specified period or lot. Non-conformance with the design
equivalent single pass opacity that would be observed at the
specifications requires corrective action and retesting. Each
stack exit.
remanufactured opacity monitor must be tested to demonstrate
3.2.24.2 Discussion—A number of similar terms are found
conformancewiththedesignspecifications.Thetestfrequency,
in the literature, manufacturer operating manuals, and in
transmissometer installation pathlength (that is, set-up dis-
common usage. OPLR (optical pathlength ratio) and STR
tance) and pathlength correction factor for each design speci-
(stack taper ratio) are common. The OPLR is equal to one half
fication test are summarized in Table 2.
of the pathlength correction. Refer to the instrument manufac-
turer for the proper factor. 4.3 This practice includes manufacturer’s performance
specifications and test procedures for (1) instrument response
3.2.24.3 Discussion—Warning—In cases where the PLCF
time, (2) calibration error, (3) optical alignment sight perfor-
value is greater than typical values (for example, greater than
mance – homogeneity of light beam and detector. It also
two), the effects of measurement errors will be significantly
includes a performance check of the spectral response of the
increased.
instrument. Conformance with these performance specifica-
Opacity Monitor Optical Characteristics
tions is determined by testing each opacity monitor prior to
shipment to the end user. (The validity of the results of the
3.2.25 angle of projection (AOP), n—the total angle that
calibration error test depends upon the accuracy of the instal-
contains all of the visible (photopic) radiation projected from
lation pathlength measurements, which is provided by the end
the light source of the transmissometer at a level greater than
user.) The test frequency, transmissometer installation path-
2.5 % of its peak illuminance.
length(thatis,set-updistance)andpathlengthcorrectionfactor
3.2.26 angle of view (AOV), n—the total angle that contains
for each performance specification test are summarized in
all of the visible (photopic) radiation detected by the photode-
Table 3.
tector assembly of the transmissometer at a level greater than
4.4 This practice establishes appropriate guidelines for QA
2.5 % of the peak detector response.
programs for manufacturers of continuous opacity monitors,
3.2.27 instrument response time, n—the time required for
including corrective actions when non-conformance with
the electrical output of an opacity monitor to achieve 95 % of
specifications is detected.
a step change in the path opacity.
4.5 AnnexA1 details additional or alternative specifications
3.2.28 mean spectral response, n—themeanresponsewave-
for certifying opacity monitors for use in applications where
length of the wavelength distribution for the effective spectral
the opacity standard is less than 10 % opacity, or where the
response curve of the transmissometer.
user expects the opacity to be less than 10 % and elects to use
3.2.29 optical alignment indicator, n—a device or means to the more restrictive criteria in Annex A1. Annex A2 provides
determine objectively the optical alignment status of opacity procedures for calibration of primary neutral density attenua-
monitor components. tors.
D6216−20
TABLE 1 Summary of Manufacturer’s Specifications and
measurements. Appendix X2 provides guidelines for ensuring
Requirements
adequate performance of opacity monitors. Appendix X3
Specification Requirement
presentsanexampledatasummaryformforreportingresultsof
Spectral response peak and mean spectral response between 500 and
the manufacturer’s certification.
600 nm: less than 10 % of peak response below
400 nm and above 700 nm
5. Significance and Use
Angle of view, angle of #4° for all radiation above 2.5 % of peak
5.1 Continuous opacity monitors are required to be installed
projection
atmanystationarysourcesofairpollutionbyfederal,state,and
Insensitivity to supply ±1.0 % opacity max. change over specified range of
local air pollution control agency regulations. EPAregulations
voltage variations supply voltage variation, or ±10 % variation from the
regarding the design and performance of opacity monitoring
nominal supply voltage
systems for sources subject to “Standards of Performance for
Thermal stability ±2.0 % opacity change per 22 °C change over
New Stationary Sources” are found in 40 CFR 60, Subpart A
specified operational range
General Provisions, §60.13 Monitoring Provisions, Appendix
Insensitivity to ambient ±2.0 % opacity max. change for solar radiation level
B, Performance Specification 1, and in applicable source-
light of $900 W/m
specific subparts. Many states have adopted these or very
similar requirements for opacity monitoring systems.
External audit filter required
access
5.2 Regulated industrial facilities are required to report
External zero device ±1.0 % opacity
continuous opacity monitoring data to control agencies on a
repeatability – optional
periodic basis. The control agencies use the data as an indirect
measure of particulate emission levels and as an indicator of
Automated calibration check of all active analyzer internal optics with
checks power or curvature, all active electronic circuitry the adequacy of process and control equipment operation and
including the light source and photodetector
maintenance practices.
assembly, and electric or electro-mechanical
systems used during normal measurement
5.3 EPA Performance Specification 1 provides minimum
operation
specifications for opacity monitors and requires source owners
or operators of regulated facilities to demonstrate that their
Simulated zero check simulated condition during which the energy
device reaching the detector is between 90 and 110 % of
installed systems meet certain design and performance speci-
the energy reaching the detector under actual clear
fications. Performance Specification 1 adopts this ASTM
path conditions
practice by reference so that manufacturers can demonstrate
Upscale calibration check check of the measurement system where the
conformance with certain design specifications by selecting
device energy level reaching the detector is between the
and testing representative instruments.
energy levels corresponding to 10 % opacity and
the highest level filter used to determine calibration
5.4 Experience demonstrated that EPA Performance Speci-
error
fication 1 prior to the Aug. 10, 2000 revisions did not address
Status indicators manufacturer to identify and specify
all of the important design and performance parameters for
opacity monitoring systems. The additional design and perfor-
Pathlength correction manufacturer to specify one of three options
mance specifications included in this practice are needed to
factor security
eliminate many of the performance problems that were previ-
Measurement output 0.5 % opacity over measurement range from –5 %
ously encountered. This practice also provides purchasers and
resolution to 50 % opacity, or higher value
vendors flexibility, by designing the test procedures for basic
Measurement and sampling and analyzing at least every 10 s:
transmissometer components or opacity monitors, or in certain
recording frequency calculate averages from at least 6 measurements
cases, complete opacity monitoring systems. However, the
per minute
specifications and test procedures are also sufficiently detailed
Instrument response time #10 s to 95 % of final value
to support the manufacturer’s certification and to facilitate
independent third party evaluations of the procedures used.
Calibration error #3.0 % opacity for the sum of the absolute value of
mean difference and 95 % confidence coefficient for
5.5 Purchasers of opacity monitoring equipment meeting all
each of three test filters
of the requirements of this practice are assured that the opacity
Optical alignment clear indication of misalignment at or before the
monitoring equipment meets all of the applicable requirements
indicator – (uniformity of point where opacity changes ±2.0 % due to
of EPA Performance Specification 1 for which the manufac-
light beam and detector) misalignment as system is misaligned both linearly
and rotationally in horizontal and vertical planes turer can certify conformance. Purchasers can rely on the
manufacturer’s published operating range specifications for
Calibration device #1.5 % opacity
ambient temperature and supply voltage. These purchasers are
repeatability
also assured that the specific instrument has been tested at the
point of manufacture and demonstrated to meet the manufac-
turer’s performance specifications for instrument response
4.6 Appendix X1 provides error budgets and estimates of time, calibration error (based on pathlength measurements
measurement uncertainty for opacity monitors that conform provided by the end user), optical alignment, and the spectral
with requirements of the main part of this practice or conform response performance check requirement. Conformance with
with the requirements in Annex A1 for low level opacity the requirements of this practice ensures conformance with all
D6216−20
TABLE 2 Manufacturer’s Design Specifications – Test Frequency, Set-Up Distance, and Pathlength Correction Factor
Pathlength Correction
Manufacturer’s Design Specification Test Frequency Set-Up Distance
Factor
Spectral Response annually, and following failure of spectral response 1 to 3 m when measured (not applicable NA
A
performance check when spectral response is calculated)
Angle of view, angle of projection monthly, or 1 in 20 units (whichever is more 3.00 m NA
frequent)
Insensitivity to supply voltage monthly, or 1 in 20 units (whichever is more 3.00 m 1.00
variations frequent)
B
Thermal stability annually 3.00 m (external jig 1.00
for tests)
B
Insensitivity to ambient light annually 3.00 m 1.00
B
External zero device repeatability – annually 3.00 m 1.00
optional
C
Additional design specifications as applicable
A
The spectral response is determined annually for each model and whenever there is a change in the design, manufacturing process, or component that might affect
performance. Reevaluation of the spectral response is necessary when an instrument fails to meet the spectral response performance check.
B
Annually, and whenever there is a change in the design, manufacturing process, or component that might affect performance.
C
Themanufacturershallcertifythattheopacitymonitordesignmeetstheapplicablerequirementsfor(1)externalauditfilteraccess,(2)externalzerodevice(ifapplicable),
(3) simulated zero and upscale calibration devices, (4) status indicators, (5) pathlength correction factor security, (6) measurement output resolution, and (7) measurement
recording frequency.
TABLE 3 Manufacturer’s Performance Specification – Test Applicability, Set-Up Distance and Pathlength Correction Factor
Manufacturer’s Performance Specification Test Applicability Set-Up Distance Pathlength Correction Factor
Instrument response time each instrument per actual installation per actual installation
A A
Calibration error each instrument per actual installation per actual installation
Acceptable tolerance comparing test to ±10 % reset clear path zero values ±10 %, use actual value for all
B B
actual conditions for subsequent monitoring subsequent monitoring
Optical alignment indicator – (uniformity of each instrument per actual installation per actual installation
light beam and detector)
Spectral response performance check each instrument per actual installation per actual installation
Calibration device repeatability each instrument per actual installation per actual installation
A
Default test values are provided for use where the installation pathlength and pathlength correction factor can not be determined.
B
When actual measurements are within ±10 % tolerance, a field performance audit can be performed rather than a field calibration error test at the time of installation.
of the requirements of 40 CFR 60, Appendix B, Performance 6. Procedure—Design Specification Verification
Specification 1 except those requirements for which tests are
6.1 Test Opacity Monitor Selection, Test Frequency, and
required after installation.
Summary of Tests:
5.6 The original manufacturer, or those involved in the
6.1.1 Perform the design specification verification proce-
repair, remanufacture, or resale of opacity monitors can use
dures in this section for each representative model or configu-
this practice to demonstrate that the equipment components or
ration involving substantially different optics, electronics, or
opacity monitoring systems provided meet, or exceed, or both,
software before being shipped to the end-user.
appropriate design and performance specifications.
6.1.2 At a minimum, select one opacity monitor from each
5.7 The applicable test procedures and specifications of this
month’sproduction,oroneopacitymonitorfromeachgroupof
practice are selected to address the equipment and activities
twenty opacity monitors, whichever is more frequent. Test this
that are within the control of the manufacturer; they do not
opacity monitor for (1) angle of view, (2) angle of projection,
mandate testing of the opacity system data recording equip-
and (3) insensitivity to supply voltage variations. If any design
ment or reporting.
specification is unacceptable, institute corrective action in
accordance with the established quality assurance program and
5.8 This practice also may serve as the basis for third party
remedy the cause of unacceptability for all opacity monitors
independent audits of the certification procedures used by
produced during the month or group of twenty. In addition, test
manufacturers of opacity monitoring equipment.
alloftheopacitymonitorsinthegroupandverifyconformance
5.9 This practice does not address ongoing quality assur-
withthedesignspecificationsbeforeshipmenttotheend-users.
ance procedures which are needed to maintain correct opera-
tion during the lifetime of the opacity monitor. NOTE 1—The selected opacity monitor may be the first opacity monitor
D6216−20
producedeachmonth,orthefirstopacitymonitorineachgroupoftwenty,
6.2.4.2 Set-up, optically align, and calibrate the transmis-
provided that it is representative of the entire group.
someter for operation on a pathlength of 1 to 3 m.
6.1.3 At a minimum, test one opacity monitor each year for
6.2.4.3 Connect an appropriate data recorder to the trans-
(1) spectral response, (2) thermal stability, and (3) insensitivity missometer and adjust the gain to an acceptable measurement
to ambient light. If any design specification is unacceptable,
level.
institute corrective action in accordance with the established
6.2.4.4 Placethemonochromatorintheopticalpathwiththe
quality assurance program and remedy the cause of unaccept-
slit edge at an appropriate distance from the permanently
ability for all affected opacity monitors. In addition, retest
mounted focusing lenses.
another representative opacity monitor after corrective action
6.2.4.5 Use the monochromator with a range from 350 nm
has been implemented to verify that the problem has been
to 750 nm or greater resolution. Record the response of the
resolved.
transmissometer at each wavelength in units of optical density
6.1.4 Certify that the opacity monitor design meets the
or voltage.
applicable requirements (see 6.7 – 6.13) for (1) external audit
6.2.4.6 Cover the reflector for double-pass
filter access, (2) external zero device (if applicable), (3)
transmissometers, or turn off the light source for single-pass
simulated zero and upscale calibration devices, (4) status
transmissometers, and repeat the test to compensate measure-
indicators, (5) pathlength correction factor security, (6) mea-
ment values for dark current at each wavelength.
surement output resolution, and (7) measurement recording
6.2.4.7 Determine the spectral response from the opacity
frequency. Maintain documentation of tests and data necessary
monitor double pass response and the monochromator calibra-
to support certification.
tion.
6.2 Spectral Response:
6.2.4.8 Graph the raw spectral response of the transmissom-
eter over the test range.
NOTE 2—The purpose of the spectral response specifications is to
6.2.4.9 Normalize the raw response curve to unity by
ensure that the transmissometer measures the transmittance of light within
the photopic range. The spectral response requirements ensure some level
dividing the response at 10 nm intervals by the peak response.
of consistency among opacity monitors because the determination of
6.2.5 Option 2, Calculation from Manufacturer Supplied
transmittance for effluent streams depends on the particle size,
Data—Obtain data from component suppliers that describes
wavelength, and other parameters. The spectral response requirements
the spectral characteristics of the light source, detector, filters,
also eliminate potential interfering effects due to absorption by various
gaseous constituents except NO , which can be an interferent if present in and all other optical components that are part of the instrument
abnormally high concentrations or over long pathlengths, or both. The
design and affect the spectral response of the transmissometer.
spectral response requirements apply to the entire transmissometer. Any
Ensure that such information is accurately determined using
combination of components may be used in the transmissometer so long
reliable means and that the information is representative of the
as the response of the entire transmissometer satisfies the applicable
specific components used in current production of the trans-
requirements.
missometer under evaluation. Update the information at least
6.2.1 Test Frequency—See 6.1.3. In addition, conduct this
every year or when new components are used, or both. Keep
test (1) anytime a change in the manufacturing process occurs
the information and records necessary to demonstrate its
or a change in a component that may affect the spectral
applicability to the current spectral response determination on
response of the transmissometer occurs or (2) on each opacity
file. Using the component manufacturer-supplied data, calcu-
monitor that fails the spectral response performance check in
late the effective spectral response for the transmissometer as
7.10.
follows:
6.2.2 Specification—The peak and mean spectral responses
6.2.5.1 Obtain the spectral emission curve for the source.
must occur between 500 nm and 600 nm. The response at any
The data must be applicable for the same voltages or currents,
wavelengthbelow400nmandabove700nmmustbelessthan
or both, as those used to power the source in the instrument.
10 %ofthepeakspectralresponse.Calculatethemeanspectral
6.2.5.2 Obtain the spectral sensitivity curve for the detector
response as the arithmetic mean value of the wavelength
that is being used in the system.
distribution for the effective spectral response curve of the
6.2.5.3 Obtain spectral transmittance curves for all filters
transmissometer.
and other active optical components that affect the spectral
6.2.3 Spectral Response Design Specification Verification
response.
Procedure—Determine the spectral response of the transmis-
6.2.5.4 Perform a point-wise multiplication of the data
someter by either of the procedures in 6.2.4 (Option 1) or 6.2.5
obtained in 6.2.5.1 – 6.2.5.3, at 10 nm intervals, over the range
(Option 2), then calculate the mean response wavelength from
350 to 750 nm, to yield the raw response curve for the system.
the normalized spectral response curve in accordance with
6.2.6. Option 1 is to measure the spectral response using a 6.2.5.5 Normalize the raw response curve to unity by
dividing the response at 10 nm intervals by the peak response.
variable slit monochromator. Option 2 is to determine the
spectral response from manufacturer-supplied data for the 6.2.6 Using the results from Option 1 or 2, as applicable,
active optical components of the measurement system. determine conformance to the specifications in 6.2.2. Then
6.2.4 Option 1, Monochromator—Use the following proce- calculate the mean response wavelength (response-weighted
dure: average wavelength) by (1) multiplying the response at 10 nm
6.2.4.1 Verify the performance of the monochromator using intervals by the wavelength, (2) summing all the products, and
a NIST traceable photopic band pass filter or light source, or (3) dividing by the sum of all 10 nm interval responses. Verify
both. that this result is greater than 500 nm but less than 600 nm.
D6216−20
6.2.7 Monitor-Specific Performance Check Limits— 6.3.3 AOV and AOP Design Specification Verification
Establishthemonitor-specificperformancechecklimitsforuse Procedure—Conduct the AOV and AOP tests using the proce-
in conducting the Spectral Response Performance Check (see dures given in 6.3.4 – 6.3.13.
7.10) as follows:
6.3.4 Transmissometer Configuration—Conduct the AOV
and AOP tests with the complete transmissometer assembly,
NOTE 3—The equivalent single-pass opacity from 6.2.7.2 and the
including all parts of the measurement system that may impact
single-pass opacity results corresponding to the applicable shifts from
the results. Provide a justification of (1) exactly what is
6.2.7.3 bound the acceptable limits for the spectral response performance
check.
included and excluded from the AOV and AOP tests and (2)
any test procedure modifications necessary to accommodate
6.2.7.1 Obtain a transmission filter that (1) has monotoni-
particular designs, such as those that may be required for dual
cally decreasing transmission between 500 and 600
beam designs that are chopped and synchronously detected.
nanometres, (2) has transmission greater than 80 % at 500 nm,
Include the justifications with documentation of the results.
(3) has its 50 % transmission point between 550 and 575 nm,
6.3.5 Set-Up—Focus and configure the transmissometer for
(4) has less than 20 % transmission at 600 nm and, (5) has less
a flange-to-flange installation separation distance of 3.00 m.
than 5 % transmission at all wavelengths greater than 625 nm.
Such filters are widely available. Calibrate and verify the
6.3.6 Test Fixture—Set up the AOV test fixture that incor-
transmittance of the filter as a function of wavelength initially porates (1) a movable light source along arcs of radius
and at least annually.
equivalent to 3.00 m flange-to-flange installation separation
distance, in both the horizontal and vertical directions relative
NOTE 4—A BG39 glass filter with thickness between 3 mm and 5 mm
to the normal installation orientation, and (2) recording mea-
meets this requirement.
surements at 2.5 cm increments along the arc. Similarly, set up
6.2.7.2 Calculate the expected single-pass opacity (assum-
the AOP test fixture that incorporates (1) a movable photode-
ingPLCF=1)thatwouldresultfrominsertingthetransmission
tector along an arc of radius equivalent to 3.00 m flange-to-
filter into the clear-stack path of the transmissometer by (1)
flange separation distance in both the horizontal and vertical
performing a point-wise multiplication of the square of the
directionsrelativetothenormalinstallationorientation,and(2)
transmission curve with the normalized transmissometer re-
recording measurements at 2.5 cm increments along the arc.
sponse curve, (2) summing the products, (3) dividing by the
NOTE 6—It is helpful to mount on test stands the detector and
sum of the 10 nm responses to form the double-pass
transmitter housings for single-pass transmissometers, or the transceiver
transmission,(4)calculatingthesingle-passtransmissionasthe
for double-pass transmissometers.
squarerootofthedoublepasstransmissionand,(5)calculating
the equivalent single-pass opacity. 6.3.7 Alternative Test Fixture—For the AOV test, at a
distance equivalent to a 3.00 m flange-to-flange separation
6.2.7.3 Repeat the calculations in 6.2.7.2, except use (1) the
distance from a stationary light source, mount the detector
normalized transmissometer curve shifted by +20 nm or the
housing on a turntable that can be rotated (both horizontally
amount which would cause the peak or mean spectral response
and vertically) in increments of 0.5°, corresponding to mea-
to shift to the limiting value of 600 nm, whichever shift is less,
surements displaced 2.5 cm along the arc, to a maximum angle
and (2) the normalized transmissometer curve shifted by –20
of 5° (corresponding to a distance of 26 cm along the arc) on
nmortheamountwhichwouldcausethepeakormeanspectral
either side of the alignment centerline. Similarly, for the AOP
response to shift to the limiting value of 500 nm, whichever
test, mount transmitter housing on the turntable at a distance
shift is less.
equivalent to a 3.00 m flange-to-flange separation distance
6.2.7.4 Repeat the calculations with any design changes
relative to a stationary photodetector.
involving the source, detector(s), or light transmitting optics.
Although failure of the spectral response performance check in
NOTE 7—If the turntable is capable of rotating only in either the
7.10 does not necessarily me
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D6216 − 12 D6216 − 20
Standard Practice for
Opacity Monitor Manufacturers to Certify Conformance with
Design and Performance Specifications
This standard is issued under the fixed designation D6216; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*Scope
1.1 This practice covers the procedure for certifying continuous opacity monitors. In the main part of this practice, it includes
design and performance specifications, test procedures, and quality assurance requirements to ensure that continuous opacity
monitors meet minimum design and calibration requirements, necessary in part, for accurate opacity monitoring measurements in
regulatory environmental opacity monitoring applications subject to 10 % or higher opacity standards. In Annex A1, additional or
alternative specifications are provided for certifying opacity monitors intended for use in applications where the opacity standard
is less than 10 %, or where the user expects the opacity to be less than 10 % and elects to use the more restrictive criteria in Annex
A1. In both cases, the error budgets for the opacity measurements are given in Appendix X1.
1.2 This practice applies specifically to the original manufacturer, or to those involved in the repair, remanufacture, or resale of
opacity monitors.
1.3 Test procedures that specifically apply to the various equipment configurations of component equipment that comprise either
a transmissometer, an opacity monitor, or complete opacity monitoring system are detailed in this practice.
1.4 The specifications and test procedures contained in the main part of this practice have been adopted by reference by the United
States Environmental Protection Agency (U.S. EPA). For each opacity monitor or monitoring system that the manufacturer
demonstrates conformance to this practice, the manufacturer may issue a certificate that states that opacity monitor or monitoring
system conforms with all of the applicable design and performance requirements of 40 CFR 60, Appendix B, Performance
Specification 1 except those for which tests are required after installation.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D1356 Terminology Relating to Sampling and Analysis of Atmospheres
This practice is under the jurisdiction of ASTM Committee D22 on Air Quality and is the direct responsibility of Subcommittee D22.03 on Ambient Atmospheres and
Source Emissions.
Current edition approved Oct. 1, 2012Sept. 1, 2020. Published November 2012September 2020. Originally approved in 1998. Last previous edition approved in 20072012
as D6216 – 07.D6216 – 12. DOI:10.1520/D6216-12.DOI:10.1520/D6216-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’sstandard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6216 − 20
2.2 U.S. Environmental Protection Agency Document:Documents:
40 CFR 60 Appendix B, Performance Specification 1
40 CFR 60 Appendix F, Procedure 3
2.3 Other Documents:
ISO/DIS 9004 Quality Management and Quality System Elements-Guidelines
ANSI/NCSL Z 540-1-1994 Calibration Laboratories and Measuring Equipment -– General Requirements
ISO 842 Quality Vocabulary
ISO/DIS 9004 Quality Management and Quality System Elements – Guidelines
NIST 260-116 Filter Calibration Procedures
3. Terminology
3.1 Definitions—For terminology relevant to this practice, see Terminology D1356.
3.2 Definitions of Terms Specific to This Standard:
Analyzer Equipment
3.2.1 opacity, n—measurement a measure of the degree to which particulate emissions reduce (due to absorption, reflection, and
scattering) the intensity of transmitted photopic light and obscure the view of an object through ambient air, an effluent gas stream,
or an optical medium, of a given pathlength.light is reduced as it passes through a gas, due to absorption and scattering.
3.2.1.1 Discussion—
Opacity (Op), expressed as a percent, The degree to which the view of an object against the background is obscured increases with
increasing opacity. Opacity (Op) is related to transmitted light, transmittance (T) through the equation:
Op 5 12 T 100 . (1)
~ ! ~ !
Op 5 12 T (1)
3.2.2 opacity monitor, n—an instrument that continuously determines the opacity of emissions released to the atmosphere.
3.2.2.1 Discussion—
An opacity monitor includes a transmissometer that determines the in-situ opacity, a means to correct opacity measurements to
equivalent single-pass opacity values that would be observed at the pathlength of the emission outlet, and all other interface and
peripheral equipment necessary for continuous operation.
3.2.2.2 Discussion—
An opacity monitor may include the following: (1) sample interface equipment such as filters and purge air blowers to protect the
instrument and minimize contamination of exposed optical surfaces, (2) shutters or other devices to provide protection during
power outages or failure of the sample interface, and (3) a remote control unit to facilitate monitoring the output of the instrument,
initiation of zero and upscale calibration checks, or control of other opacity monitor functions.
3.2.3 opacity monitor model, n—a specific transmissometer or opacity monitor configuration identified by the specific
measurement system design, including: (1) the use of specific light source, detector(s), lenses, mirrors, and other optical
components, (2) the physical arrangement of optical and other principal components, (3) the specific electronics configuration and
signal processing approach, (4) the specific calibration check mechanisms and drift/dust compensation devices and approaches, and
(5) the specific software version and data processing algorithms, as implemented in a particular manufacturing process, at a
particular facility and subject to an identifiable quality assurance system.
3.2.3.1 Discussion—
Changing the retro-reflector material or the size of the retro-reflector aperture is not considered to be a model change unless it
changes the basic attributes of the optical system.
3.2.3.2 Discussion—
Minor changes to software or data outputs may not be considered as a model change provided that the manufacturer documents
all such changes and provides a satisfactory explanation in a report.
3.2.4 opacity monitoring system, n—the entire set of equipment necessary to monitor continuously the in-stack opacity, average
the emission measurement data, and permanently record monitoring results.
Available from U.S. Government Printing Office, Superintendent of Documents, 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401,20401-0001,
http://www.access.gpo.gov.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Available from National Institute of Standards and Technology (NIST), 100 Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.
D6216 − 20
3.2.4.1 Discussion—
An opacity monitoring system includes at least one opacity monitor with all of its associated interface and peripheral equipment
and the specific data recording system (including software) employed by the end user. An opacity monitoring system may include
multiple opacity monitors and a common data acquisition and recording system.
3.2.5 optical density (OD), n—a logarithmic measure of the amount of incident light attenuated.
3.2.5.1 Discussion—
OD is related to transmittance and opacity as follows:
OD 5 log 1/T 52log T 52log 12 Op , (2)
~ ! ~ ! ~ !
10 10 10
OD 5 log ~1/T!52log ~T!52log ~12 Op! (2)
10 10 10
where Op is expressed as a fraction.
3.2.6 transmittance, n—the fraction of incident light within a specified optical region that passes through an optical medium.
3.2.7 transmissometer, n—an instrument that passes light through a particulate-laden effluent stream and measures in situ the
optical transmittance of that light within a specified wavelength region.
3.2.7.1 Discussion—
Single-pass transmissometers consist of a light source and detector components mounted on opposite ends of the measurement
path. Double-pass instruments consist of a transceiver (including both light source and detector components) and a reflector
mounted on opposite ends of the measurement path.
3.2.7.2 Discussion—
For the purposes of this practice, the transmissometer includes the following mechanisms (1) means to verify the optical alignment
of the components and (2) simulated zero and upscale calibration devices to check calibration drifts when the instrument is
installed on a stack or duct.
3.2.7.3 Discussion—
Transmissometers are sometimes referred to as opacity analyzers when they are configured to measure opacity.
Analyzer Zero Adjustments and Devices
3.2.8 dust compensation, n—a method or procedure for systematically adjusting the output of a transmissometer to account for
reduction in transmitted light reaching the detector (apparent increase in opacity) that is specifically due to the accumulation of
dust (that is, particulate matter) on the exposed optical surfaces of the transmissometer.
3.2.8.1 Discussion—
Dust compensation may be included as an optional feature but is not required.
3.2.8.2 Discussion—
The dust compensation is determined relative to the previous occasion when the exposed optics were cleaned and the dust
compensation was reset to zero. The determination of dust accumulation on surfaces exposed to the effluent must be limited to only
those surfaces through which the light beam passes under normal opacity measurement and the simulated zero device or equivalent
mechanism necessary for the dust compensation measurement. The determination of dust compensation is not required to include
all surfaces exposed to the effluent or dust accumulation.
3.2.8.3 Discussion—
The dust accumulation for all of the optical surfaces included in the dust compensation method must actually be measured. Unlike
zero drift, which may be either positive or negative, dust compensation can only reduce the apparent opacity. A dust compensation
procedure can correct for specific bias and provide measurement results equivalent to the clean window condition.
3.2.8.4 Discussion—
In those cases where dust compensation is used, the opacity monitor must provide a means to display the level of dust
compensation. Regulatory requirements may impose a limit on the amount of dust compensation that can be applied and require
that an alarm be activated when the limit is reached.
3.2.9 external audit device, n—an external device for simulating the zero opacity condition during a calibration error test.
3.2.10 external zero device, n—an external device for checking the zero alignment of the transmissometer by simulating the zero
opacity condition for a specific installed opacity monitor.
D6216 − 20
3.2.10.1 Discussion—
The external zero device can also be used as an external audit device provided it meets the requirements of both.
3.2.11 simulated zero device, n—an automated mechanism within the transmissometer that produces a simulated clear path
condition or low level opacity condition.
3.2.11.1 Discussion—
The simulated zero device is used to check zero drift daily or more frequently and whenever necessary (for example, after
corrective actions or repairs) to assess opacity monitor performance while the instrument is installed on the stack or duct.
3.2.11.2 Discussion—
The proper response to the simulated zero device is established under clear path conditions while the transmissometer is optically
aligned at the installation pathlength and accurately calibrated. The simulated zero device is then the surrogate, clear path
calibration value, while the opacity monitor is in service.
3.2.11.3 Discussion—
Simulated zero checks do not necessarily assess the optical alignment, the reflector status (for double-pass systems), or the dust
contamination level on all optical surfaces. (See also 6.9.1.)
3.2.12 zero alignment, n—the process of establishing the quantitative relationship between the simulated zero device and the actual
clear path opacity responses of a transmissometer.
3.2.13 zero compensation, n—an automatic adjustment of the transmissometer to achieve the correct response to the simulated
zero device.
3.2.13.1 Discussion—
The zero compensation adjustment is fundamental to the transmissometer design and may be inherent to its operation (for example,
continuous adjustment based on comparison to reference values/conditions, use of automatic control mechanisms, rapid
comparisons with simulated zero and upscale calibration drift check values, and so forth) or it may occur each time a calibration
check cycle (zero and upscale calibration drift check) is performed by applying either analog or digital adjustments within the
transmissometer.
3.2.13.2 Discussion—
For opacity monitors that do not distinguish between zero compensation and dust compensation, the accumulated zero
compensation may be designated as the dust compensation. Regulatory requirements may impose a limit on the amount of dust
compensation that can be applied and require that an alarm be activated when the limit is reached.
3.2.14 zero drift, n—the difference between the opacity monitor response to the simulated zero device and its nominal value
(reported as percent opacity) after a period of normal continuous operation during which no maintenance, repairs, or external
adjustments to the opacity monitor took place.
3.2.14.1 Discussion—
Zero drift may occur due to changes in the light source, changes in the detector, variations due to internal scattering, changes in
electronic components, or varying environmental conditions such as temperature, voltage or other external factors. Depending on
the design of the transmissometer, particulate matter (that is, dust) deposited on optical surfaces may contribute to zero drift. Zero
drift may be positive or negative.
Calibrations and Adjustments
3.2.15 attenuator, n—a glass or grid filter that reduces the transmittance of light.
3.2.16 calibration drift, n—the difference between the opacity monitor response to the upscale calibration device and its nominal
value after a period of normal continuous operation during which no maintenance, repairs, or external adjustments to the opacity
monitor took place.
3.2.16.1 Discussion—
Calibration drift may be determined after determining and correcting for zero drift. For opacity monitors that include automatic
zero compensation or dust compensation features, calibration drift may be determined after zero drift or dust compensation, or
both, are applied.
3.2.17 calibration error, n—the sum of the absolute value of the mean difference and confidence coefficient for the opacity values
indicated by an optically aligned opacity monitor (laboratory test) or opacity monitoring system (field test) as compared to the
known values of three calibration attenuators under clear path conditions.
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3.2.17.1 Discussion—
The calibration error indicates the fundamental calibration status of the opacity.
3.2.18 external adjustment, n—either (1) a physical adjustment to a component of the opacity monitoring system that affects its
response or its performance, or (2) an adjustment applied by the data acquisition system (for example, mathematical adjustment
to compensate for drift) which is external to the transmissometer and control unit, if applicable.
3.2.18.1 Discussion—
External adjustments are made at the election of the end user but may be subject to various regulatory requirements.
3.2.19 intrinsic adjustment, n—an automatic and essential feature of an opacity monitor that provides for the internal control of
specific components or adjustment of the opacity monitor response in a manner consistent with the manufacturer’smanufacturer’s
design of the instrument and its intended operation.
3.2.19.1 Discussion—
Examples of intrinsic adjustments include automatic gain control used to maintain signal amplitudes constant with respect to some
reference value, or the technique of ratioing the measurement and reference beams in dual beam systems. Intrinsic adjustments are
either non-elective or are configured in accordance with factory recommended procedures; they are not subject to change from time
to time at the discretion of the end user.
3.2.20 upscale calibration device, n—an automated mechanism (employing a filter or reduced reflectance device) within the
transmissometer that produces an upscale opacity value.
3.2.20.1 Discussion—
The upscale calibration device is used to check the upscale drift of the measurement system. It may be used in conjunction with
the simulated zero device (for example, filter superimposed on simulated zero reflector) or a parallel fashion (for example, zero
and upscale (reduced reflectance) devices applied to the light beam sequentially). (See also 6.9.2.)
Opacity Monitor Location Characteristics
3.2.21 installation pathlength, n—the installation flange-to-flange separation distance between the transceiver and reflector for a
double-pass transmissometer or between the transmitter and receiver for a single-pass transmissometer.
3.2.22 monitoring pathlength, n—the effective single pass depth of effluent between the receiver and the transmitter of a
single-pass transmissometer, or between the transceiver and reflector of a double-pass transmissometer at the installation location.
3.2.23 emission outlet pathlength, n—the physical pathlength (single pass depth of effluent) at the location where emissions are
released to the atmosphere.
3.2.23.1 Discussion—
For circular stacks, the emission outlet pathlength is the internal diameter at the stack exit. For non-circular outlets, the emission
outlet pathlength is the hydraulic diameter. For rectangular stacks:
D 5 2LW / L1W , (3)
~ ! ~ !
D 5 2LW / L1W (3)
~ ! ~ !
where L is the length of the outlet and W is the width of the stack exit.
3.2.24 pathlength correction factor (PLCF), n—the ratio of the emission outlet pathlength to the monitoring pathlength.
3.2.24.1 Discussion—
The PLCF is used to calculate the equivalent single pass opacity that would be observed at the stack exit.
3.2.24.2 Discussion—
A number of similar terms are found in the literature, manufacturer operating manuals, and in common usage. OPLR (optical
pathlength ratio) and STR (stack taper ratio) are common. The OPLR is equal to one half of the pathlength correction. Refer to
the instrument manufacturer for the proper factor.
3.2.24.3 Discussion—
Warning—In cases where the PLCF value is greater than typical values,values (for example, greater than two)two), the effects
of measurement errors will be significantly increased.
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Opacity Monitor Optical Characteristics
3.2.25 angle of projection (AOP), n—the total angle that contains all of the visible (photopic) radiation projected from the light
source of the transmissometer at a level greater than 2.5 % of its peak illuminance.
3.2.26 angle of view (AOV), n—the total angle that contains all of the visible (photopic) radiation detected by the photodetector
assembly of the transmissometer at a level greater than 2.5 % of the peak detector response.
3.2.27 instrument response time, n—the time required for the electrical output of an opacity monitor to achieve 95 % of a step
change in the path opacity.
3.2.28 mean spectral response, n—the mean response wavelength of the wavelength distribution for the effective spectral response
curve of the transmissometer.
3.2.29 optical alignment indicator, n—a device or means to determine objectively the optical alignment status of opacity monitor
components.
3.2.30 peak spectral response, n—the wavelength of maximum sensitivity of the transmissometer.
3.2.31 photopic, n—a region of the electromagnetic spectrum defined by the response of the light-adapted human eye as
characterized in the “Source C, Human Eye Response” contained in 40 CFR 60, Appendix B, Performance Specification 1.
4. Summary of Practice
4.1 A comprehensive series of specifications and test procedures that opacity monitor manufacturers must use to certify opacity
monitoring equipment (that is, that the equipment meets minimum design and performance requirements) prior to shipment to the
end user is provided. The design and performance specifications are summarized in Table 1.
4.2 Design specifications and test procedures for (1) peak and mean spectral responses, (2) angle of view and angle of projection,
(3) insensitivity to supply voltage variations, (4) thermal stability, (5) insensitivity to ambient light, and (6) an optional procedure
for opacity monitors with external zero devices which regulatory agencies may require are included. The manufacturer periodically
selects and tests for conformance with these design specifications an instrument that is representative of a group of instruments)
produced during a specified period or lot. Non-conformance with the design specifications requires corrective action and retesting.
Each remanufactured opacity monitor must be tested to demonstrate conformance with the design specifications. The test
frequency, transmissometer installation pathlength (that is, set-up distance) and pathlength correction factor for each design
specification test are summarized in Table 2.
4.3 This practice includes manufacturer’smanufacturer’s performance specifications and test procedures for (1) instrument
response time, (2) calibration error, (3) optical alignment sight performance -– homogeneity of light beam and detector. It also
includes a performance check of the spectral response of the instrument. Conformance with these performance specifications is
determined by testing each opacity monitor prior to shipment to the end user. (The validity of the results of the calibration error
test depends upon the accuracy of the installation pathlength measurements, which is provided by the end user.) The test frequency,
transmissometer installation pathlength (that is, set-up distance) and pathlength correction factor for each performance
specification test are summarized in Table 3.
4.4 This practice establishes appropriate guidelines for QA programs for manufacturers of continuous opacity monitors, including
corrective actions when non-conformance with specifications is detected.
4.5 Annex A1 details additional or alternative specifications for certifying opacity monitors for use in applications where the
opacity standard is less than 10 % opacity, or where the user expects the opacity to be less than 10 % and elects to use the more
restrictive criteria in Annex A1. Annex A2 provides procedures for calibration of primary neutral density attenuators.
4.6 Appendix X1 provides error budgets and estimates of measurement uncertainty for opacity monitors that conform with
requirements of the main part of this practice or conform with the requirements in Annex A1 for low level opacity measurements.
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TABLE 1 Summary of Manufacturer’sManufacturer’s
Specifications and Requirements
Specification Requirement
Specification Requirement
Spectral response peak and mean spectral response between 500 and
600 nm: less than 10% of peak response below 400
nm and above 700 nm
Spectral response peak and mean spectral response between 500 and
600 nm: less than 10 % of peak response below
400 nm and above 700 nm
Angle of view, angle of #4° for all radiation above 2.5 % of peak
projection
Insensitivity to supply ±1.0 % opacity max. change over specified range of
voltage variations supply voltage variation, or ±10 % variation from the
nominal supply voltage
Thermal stability ±2.0 % opacity change per 22°C (40°F) change
over specified operational range
Thermal stability ±2.0 % opacity change per 22 °C change over
specified operational range
Insensitivity to ambient ±2.0 % opacity max. change for solar radiation level
light of $900 W/m
External audit filter required
access
External zero device ±1.0 % opacity
repeatability - Optional
External zero device ±1.0 % opacity
repeatability – optional
Automated calibration check of all active analyzer internal optics with
checks power or curvature, all active electronic circuitry
including the light source and photodetector
assembly, and electric or electro-mechanical
systems used during normal measurement
operation
Simulated zero check simulated condition during which the energy
device reaching the detector is between 90 and 110 % of
the energy reaching the detector under actual clear
path conditions
Upscale calibration check check of the measurement system where the
device energy level reaching the detector is between the
energy levels corresponding to 10 % opacity and
the highest level filter used to determine calibration
error
Status indicators manufacturer to identify and specify
Pathlength correction manufacturer to specify one of three options
factor security
Measurement output 0.5 % opacity over measurement range from -5 % to
resolution 50 % opacity, or higher value
Measurement output 0.5 % opacity over measurement range from –5 %
resolution to 50 % opacity, or higher value
Measurement and sampling and analyzing at least every 10 s:
recording frequency calculate averages from at least 6 measurements
per minute
Instrument response time #10 s to 95 % of final value
Calibration error #3.0 % opacity for the sum of the absolute value of
mean difference and 95 % confidence coefficient for
each of three test filters
Optical alignment clear indication of misalignment at or before the
indicator - (uniformity of point where opacity changes ±2.0 % due to
light beam and detector) misalignment as system is misaligned both linearly
and rotationally in horizontal and vertical planes
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Specification Requirement
Optical alignment clear indication of misalignment at or before the
indicator – (uniformity of point where opacity changes ±2.0 % due to
light beam and detector) misalignment as system is misaligned both linearly
and rotationally in horizontal and vertical planes
Calibration device #1.5 % opacity
repeatability
Appendix X2 provides guidelines for ensuring adequate performance of opacity monitors. Appendix X3 presents an example data
summary form for reporting results of the manufacturer’s certification.
5. Significance and Use
5.1 Continuous opacity monitors are required to be installed at many stationary sources of air pollution by federal, state, and local
air pollution control agency regulations. EPA regulations regarding the design and performance of opacity monitoring systems for
sources subject to “Standards of Performance for New Stationary Sources” are found in 40 CFR 60, Subpart A General Provisions,
§60.13 Monitoring Provisions, Appendix B, Performance Specification 1, and in applicable source-specific subparts. Many states
have adopted these or very similar requirements for opacity monitoring systems.
5.2 Regulated industrial facilities are required to report continuous opacity monitoring data to control agencies on a periodic basis.
The control agencies use the data as an indirect measure of particulate emission levels and as an indicator of the adequacy of
process and control equipment operation and maintenance practices.
5.3 EPA Performance Specification 1 provides minimum specifications for opacity monitors and requires source owners or
operators of regulated facilities to demonstrate that their installed systems meet certain design and performance specifications.
Performance Specification 1 adopts this ASTM practice by reference so that manufacturers can demonstrate conformance with
certain design specifications by selecting and testing representative instruments.
5.4 Experience demonstrated that EPA Performance Specification 1 prior to the AugustAug. 10, 2000 10, 2000 revisions did not
address all of the important design and performance parameters for opacity monitoring systems. The additional design and
performance specifications included in this practice are needed to eliminate many of the performance problems that were
previously encountered. This practice also provides purchasers and vendors flexibility, by designing the test procedures for basic
transmissometer components or opacity monitors, or in certain cases, complete opacity monitoring systems. However, the
specifications and test procedures are also sufficiently detailed to support the manufacturer’smanufacturer’s certification and to
facilitate independent third party evaluations of the procedures used.
5.5 Purchasers of opacity monitoring equipment meeting all of the requirements of this practice are assured that the opacity
monitoring equipment meets all of the applicable requirements of EPA Performance Specification 1 for which the manufacturer
can certify conformance. Purchasers can rely on the manufacturer’smanufacturer’s published operating range specifications for
ambient temperature and supply voltage. These purchasers are also assured that the specific instrument has been tested at the point
of manufacture and demonstrated to meet the manufacturer’smanufacturer’s performance specifications for instrument response
time, calibration error (based on pathlength measurements provided by the end user), optical alignment, and the spectral response
performance check requirement. Conformance with the requirements of this practice ensures conformance with all of the
requirements of 40 CFR 60, Appendix B, Performance Specification 1 except those requirements for which tests are required after
installation.
5.6 The original manufacturer, or those involved in the repair, remanufacture, or resale of opacity monitors can use this practice
to demonstrate that the equipment components or opacity monitoring systems provided meet, or exceed, or both, appropriate design
and performance specifications.
5.7 The applicable test procedures and specifications of this practice are selected to address the equipment and activities that are
within the control of the manufacturer; they do not mandate testing of the opacity system data recording equipment or reporting.
5.8 This practice also may serve as the basis for third party independent audits of the certification procedures used by
manufacturers of opacity monitoring equipment.
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TABLE 2 Manufacturer’sManufacturer’s Design Specifications – Test Frequency, Set-Up Distance, and Pathlength Correction Factor
Pathlength Correction
Manufacturer’s Design Specification Test Frequency Set-Up Distance
Factor
Manufacturer’s Design Specification Test Frequency Set-Up Distance Pathlength Correction
Factor
Spectral Response annually, and following failure of spectral response 1 to 3 m when measured (not applicable NA
A
performance check when spectral response is calculated)
Angle of view, angle monthly, or 1 in 20 units (whichever is more 3.00 m NA
of projection frequent)
Insensitivity to supply voltage monthly, or 1 in 20 units (whichever is more 3.00 m 1.00
variations frequent)
B
Thermal stability annually 3.00 m (external jig 1.00
for tests)
B
Insensitivity to annually 3.00 m 1.00
ambient light
B
External zero device repeatability - annually 3.00 m 1.00
optional
B
External zero device repeatability – annually 3.00 m 1.00
optional
C
Additional design specifications as applicable
A
The spectral response is determined annually for each model and whenever there is a change in the design, manufacturing process, or component that might affect
performance. Reevaluation of the spectral response is necessary when an instrument fails to meet the spectral response performance check.
B
Annually, and whenever there is a change in the design, manufacturing process, or component that might affect performance.
C
The manufacturer shall certify that the opacity monitor design meets the applicable requirements for (a1) external audit filter access, (b2) external zero device (if
applicable), (c3) simulated zero and upscale calibration devices, (d4) status indicators, (e5) pathlength correction factor security, (f6) measurement output resolution, and
(g7) measurement recording frequency.
TABLE 3 Manufacturer’sManufacturer’s Performance Specification – Test Applicability, Set-Up Distance and Pathlength Correction
Factor
Manufacturer’s Performance Specification Test Applicability Set-Up Distance Pathlength Correction Factor
Manufacturer’s Performance Specification Test Applicability Set-Up Distance Pathlength Correction Factor
Instrument response time each instrument per actual installation per actual installation
A A
Calibration error each instrument per actual installation per actual installation
Acceptable tolerance comparing test to ±10 % reset clear path zero values ±10 %, use actual value for all
B B
actual conditions for subsequent monitoring subsequent monitoring
Optical alignment indicator - (uniformity of each instrument per actual installation per actual installation
light beam and detector)
Optical alignment indicator – (uniformity of each instrument per actual installation per actual installation
light beam and detector)
Spectral response performance check each instrument per actual installation per actual installation
Calibration device repeatability each instrument per actual installation per actual installation
A
Default test values are provided for use where the installation pathlength and pathlength correction factor can not be determined.
B
When actual measurements are within ±10 % tolerance, a field performance audit can be performed rather than a field calibration error test at the time of installation.
5.9 This practice does not address ongoing quality assurance procedures which are needed to maintain correct operation during
the lifetime of the opacity monitor.
6. Procedure—Design Specification Verification
6.1 Test Opacity Monitor Selection, Test Frequency, and Summary of Tests:
6.1.1 Perform the design specification verification procedures in this section for each representative model or configuration
involving substantially different optics, electronics, or software before being shipped to the end-user.
6.1.2 At a minimum, select one opacity monitor from each month’smonth’s production, or one opacity monitor from each group
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of twenty opacity monitors, whichever is more frequent. Test this opacity monitor for (1) angle of view, (2) angle of projection,
and (3) insensitivity to supply voltage variations. If any design specification is unacceptable, institute corrective action in
accordance with the established quality assurance program and remedy the cause of unacceptability for all opacity monitors
produced during the month or group of twenty. In addition, test all of the opacity monitors in the group and verify conformance
with the design specifications before shipment to the end-users.
NOTE 1—The selected opacity monitor may be the first opacity monitor produced each month, or the first opacity monitor in each group of twenty,
provided that it is representative of the entire group.
6.1.3 At a minimum, test one opacity monitor each year for (1) spectral response, (2) thermal stability, and (3) insensitivity to
ambient light. If any design specification is unacceptable, institute corrective action in accordance with the established quality
assurance program and remedy the cause of unacceptability for all affected opacity monitors. In addition, retest another
representative opacity monitor after corrective action has been implemented to verify that the problem has been resolved.
6.1.4 Certify that the opacity monitor design meets the applicable requirements (see 6.7 – 6.13) for (1) external audit filter access,
(2) external zero device (if applicable), (3) simulated zero and upscale calibration devices, (4) status indicators, (5) pathlength
correction factor security, (6) measurement output resolution, and (7) measurement recording frequency. Maintain documentation
of tests and data necessary to support certification.
6.2 Spectral Response:
NOTE 2—The purpose of the spectral response specifications is to ensure that the transmissometer measures the transmittance of light within the photopic
range. The spectral response requirements ensure some level of consistency among opacity monitors because the determination of transmittance for
effluent streams depends on the particle size, wavelength, and other parameters. The spectral response requirements also eliminate potential interfering
effects due to absorption by various gaseous constituents except NO , which can be an interferent if present in abnormally high concentrations or over
long pathlengths, or both. The spectral response requirements apply to the entire transmissometer. Any combination of components may be used in the
transmissometer so long as the response of the entire transmissometer satisfies the applicable requirements.
6.2.1 Test Frequency—See 6.1.3. In addition, conduct this test (1) anytime a change in the manufacturing process occurs or a
change in a component that may affect the spectral response of the transmissometer occurs or (2) on each opacity monitor that fails
the spectral response performance check in 7.10.
6.2.2 Specification—The peak and mean spectral responses must occur between 500 nm and 600 nm. The response at any
wavelength below 400 nm and above 700 nm must be less than 10 % of the peak spectral response. Calculate the mean spectral
response as the arithmetic mean value of the wavelength distribution for the effective spectral response curve of the
transmissometer.
6.2.3 Spectral Response Design Specification Verification Procedure—Determine the spectral response of the transmissometer by
either of the procedures in 6.2.4 (Option 1) or 6.2.5 (Option 2), then calculate the mean response wavelength from the normalized
spectral response curve in accordance with 6.2.6. Option 1 is to measure the spectral response using a variable slit monochromator.
Option 2 is to determine the spectral response from manufacturer-supplied data for the active optical components of the
measurement system.
6.2.4 Option 1, Monochromator—Use the following procedure:
6.2.4.1 Verify the performance of the monochromator using a NIST traceable photopic band pass filter or light source, or both.
6.2.4.2 Set-up, optically align, and calibrate the transmissometer for operation on a pathlength of 1 to 3 m.
6.2.4.3 Connect an appropriate data recorder to the transmissometer and adjust the gain to an acceptable measurement level.
6.2.4.4 Place the monochromator in the optical path with the slit edge at an appropriate distance from the permanently mounted
focusing lenses.
6.2.4.5 Use the monochromator with a range from 350 nm to 750 nm or greater resolution. Record the response of the
transmissometer at each wavelength in units of optical density or voltage.
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6.2.4.6 Cover the reflector for double-pass transmissometers, or turn off the light source for single-pass transmissometers, and
repeat the test to compensate measurement values for dark current at each wavelength.
6.2.4.7 Determine the spectral response from the opacity monitor double pass response and the monochromator calibration.
6.2.4.8 Graph the raw spectral response of the transmissometer over the test range.
6.2.4.9 Normalize the raw response curve to unity by dividing the response at 10 nm intervals by the peak response.
6.2.5 Option 2, Calculation from Manufacturer Supplied Data—Obtain data from component suppliers that describes the spectral
characteristics of the light source, detector, filters, and all other optical components that are part of the instrument design and affect
the spectral response of the transmissometer. Ensure that such information is accurately determined using reliable means and that
the information is representative of the specific components used in current production of the transmissometer under evaluation.
Update the information at least every year or when new components are used, or both. Keep the information and records necessary
to demonstrate its applicability to the current spectral response determination on file. Using the component manufacturer-supplied
data, calculate the effective spectral response for the transmissometer as follows:
6.2.5.1 Obtain the spectral emission curve for the source. The data must be applicable for the same voltages or currents, or both,
as those used to power the source in the instrument.
6.2.5.2 Obtain the spectral sensitivity curve for the detector that is being used in the system.
6.2.5.3 Obtain spectral transmittance curves for all filters and other active optical components that affect the spectral response.
6.2.5.4 Perform a point-wise multiplication of the data obtained in 6.2.5.1 – 6.2.5.3, at 10 nm intervals, over the range 350 to 750
nm, to yield the raw response curve for the system.
6.2.5.5 Normalize the raw response curve to unity by dividing the response at 10 nm intervals by the peak response.
6.2.6 Using the results from Option 1 or 2, as applicable, determine conformance to the specifications in 6.2.2. Then calculate the
mean response wavelength (response-weighted average wavelength) by (1) multiplying the response at 10 nm intervals by the
wavelength, (2) summing all the products, and (3) dividing by the sum of all 10 nm interval responses. Verify that this result is
greater than 500 nm but less than 600 nm.
6.2.7 Monitor-Specific Performance Check Limits—Establish the monitor-specific performance check limits for use in conducting
the Spectral Response Performance Check (see 7.10) as follows:
NOTE 3—The equivalent single-pass opacity from 6.2.7.2 and the single-pass opacity results corresponding to the applicable shifts from 6.2.7.3 bound
the acceptable limits for the spectral response performance check.
6.2.7.1 Obtain a transmission filter that (1) has monotonically decreasing transmission between 500 and 600 nanometres, (2) has
transmission greater than 80 % at 500 nm, (3) has its 50 % transmission point between 550 and 575 nm, (4) has less than 20 %
transmission at 600 nm and, (5) has less than 5 % transmission at all wavelengths greater than 625 nm. Such filters are widely
available. Calibrate and verify the transmittance of the filter as a function of wavelength initially and at least annually.
NOTE 4—A BG39 glass filter with thickness between 3 mm and 5 mm meets this requirement.
6.2.7.2 Calculate the expected single-pass opacity (assuming PLCF=1) PLCF = 1) that would result from inserting the
transmission filter into the clear-stack path of the transmissometer by (1) performing a point-wise multiplication of the square of
the transmission curve with the normalized transmissometer response curve, (2) summing the products, (3) dividing by the sum
of the 10 nm responses to form the double-pass transmission, (4) calculating the single-pass transmission as the square root of the
double pass transmission and, (5) calculating the equivalent single-pass opacity.
6.2.7.3 Repeat the calculations in 6.2.7.2, except use (1) the normalized transmissometer curve shifted by +20 nm or the amount
which would cause the peak or mean spectral response to shift to the limiting value of 600 nm, whichever shift is less, and (2)
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the normalized transmissometer curve shifted by –20 nm or the amount which would cause the peak or mean spectral response
to shift to the limiting value of 500 nm, wh
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