ASTM D6543-15

Standard Guide to the Evaluation of Measurements Made by Online Coal Analyzers

SIGNIFICANCE AND USE
5.1 Online analyzers are used to provide quality data on lots of coal. The resulting quality data are used as a production tool or for some contractual application. This guide provides the means of evaluating the analyzer system and the data produced.  
5.2 Become familiar with the document's terminology and layout. The section on test design and data collection will provide the means by which all the analysis data will be gathered. The test should be carefully designed to ensure the user’s requirements are met.  
5.3 The procedures defined in this guide can be used to estimate the accuracy and precision of an online analyzer, (1) to conduct acceptance testing following installation and (2) to monitor the accuracy and precision (a) during routine use (quality control), (b) when significant changes are made to the analyzer, and (c) when a significant change in the coal being analyzed occurs (e.g., a different seam at a mine, or a new coal source at a power plant). These procedures can also be used for calibration purposes.
SCOPE
1.1 This guide provides techniques to be used for the evaluation of the measurement performance of online coal analyzers.  
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-Dec-2014
• ICS: 73.040 - Coals
• Technical Committee: D05 - Coal and Coke
• Drafting Committee: D05.23 - Sampling

Relations

• Replaces: ASTM D6543-14b - Standard Guide to the Evaluation of Measurements Made by Online Coal Analyzers
• Effective Date: 01-Jan-2015
• Replaced By: ASTM D6543-17 - Standard Guide to the Evaluation of Measurements Made by Online Coal Analyzers
• Effective Date: 01-Jun-2017

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D6543 − 15
Standard Guide to
the Evaluation of Measurements Made by Online Coal
Analyzers
This standard is issued under the fixed designation D6543; 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 3.2.3 full-stream analyzer, n—an analyzer system that inter-
rogates the coal on a process belt.
1.1 This guide provides techniques to be used for the
evaluation of the measurement performance of online coal 3.2.4 Latent Variable Model, n—a mathematical model that
analyzers.
can estimate each system’s precision, when the analyzer is
compared to two independent reference systems.
1.2 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3.2.5 online analyzer, n—an analytical tool consisting of an
responsibility of the user of this standard to establish appro-
instrumentandsystems,whichtogetherprovidemeasurements,
priate safety and health practices and determine the applica-
or estimates, or both, of coal quality parameters.
bility of regulatory limitations prior to use.
3.2.6 outlier, n—an extreme value that statistical tests indi-
cate to be far enough from other results in a population under
2. Referenced Documents
consideration to cause suspicion that the value is not a member
2.1 ASTM Standards:
of the population.
D121 Terminology of Coal and Coke
3.2.7 reference material, n—material of stable composition
D2013 Practice for Preparing Coal Samples for Analysis
that may be used to generate static analyzer measurements.
D2234/D2234M Practice for Collection of a Gross Sample
of Coal
3.2.8 reference system, n—a measurement system used to
D6518 Practice for Bias Testing a Mechanical Coal Sam-
measure the characteristics of a lot of coal that are also
pling System (Withdrawn 2008)
measured by an online analyzer, and against which the online
D7430 Practice for Mechanical Sampling of Coal
analyzer measurements are compared.
E178 Practice for Dealing With Outlying Observations
3.2.9 sample stream analyzer, n—an analyzer system that is
fed a save or reject stream from a sampling system.
3. Terminology
3.2.10 standardization, n—calibration of an instrument to a
3.1 Definitions—For additional definitions of terms used in
reference material using static stability measurements.
this standard, refer to Terminology D121.
3.2.11 static stability, n—an estimate of the measurement
3.2 Definitions of Terms Specific to This Standard:
precision of an instrument obtained on material that is not
3.2.1 analyzer system, n—a coal quality measurement sys-
moving. The estimate normally is expressed as the standard
tem which includes an online coal analyzer and which may
deviation and average of the measurements for a given period
include one or more stages of a coal-sampling system.
of time.
3.2.2 calibration, n—mathematical modeling of analyzer
3.2.12 synchronization error, n—an error that occurs from
and comparative coal sampling and analysis data. Factors from
the model are used in the online analyzer control software. comparing measurements made by an online analyzer and a
reference system that are not measuring exactly the same lot
because of temporal and/or spatial offsets.
This guide is under the jurisdiction of ASTM Committee D05 on Coal and
Coke and is the direct responsibility of Subcommittee D05.23 on Sampling.
4. Summary of Guide
Current edition approved Jan. 1, 2015. Published January 2015. Originally
approved in 2000. Last previous edition approved in 2014 as D6543-14b. DOI:
4.1 This guide describes how to measure performance of an
10.1520/D6543-15.
online analyzer using comparative measurements. The perfor-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
mance evaluation consists of a paired comparison of analyses
Standards volume information, refer to the standard’s Document Summary page on
from a reference method using ASTM sampling, sample
the ASTM website.
preparation, and analysis methods for several lots of coal with
The last approved version of this historical standard is referenced on
www.astm.org. the analyses from the online analyzer for the same lots of coal.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6543 − 15
The data resulting from the comparative test may be evaluated 6.1.5 Additional changes which could merit performance
using graphical and statistical techniques outlined below. testing include a change in the material or width of the
conveyor, or coal flow rates (in the case of full-flow analyzers).
4.2 Varioustechniquesarerecommendedbyonlineanalyzer
manufacturers for standardization or static testing. These
6.2 Static Stability Measurements for Baseline
techniques are useful for establishing a benchmark before
Assessment—A reference material may be used to provide a
conducting a comparative test. These techniques may also be
baseline assessment of static measurement precision. The
used as diagnostic tests in accordance with methods recom-
reference material may be used to compare current mean and
mended by online analyzer manufacturers and graphical and
standard deviation values with mean and standard deviation
statistical techniques included in this guide.
values, previously collected in the same manner. The resulting
comparative data may help determine whether any apparent
5. Significance and Use
decline in analyzer dynamic performance may be attributed to
5.1 Online analyzers are used to provide quality data on lots
a change in the operating characteristics of the analyzer, in the
of coal.The resulting quality data are used as a production tool
absenceoftheinfluenceofsampling,preparation,andanalysis.
or for some contractual application. This guide provides the
6.2.1 The results of this evaluation can indicate whether
means of evaluating the analyzer system and the data pro-
analyzer precision has significantly degraded or whether a bias
duced.
may have occurred. If so, it may be possible to adjust the
5.2 Become familiar with the document’s terminology and analyzer to restore initial performance. If the user wishes only
layout. The section on test design and data collection will
to measure current static stability, any available coal may be
provide the means by which all the analysis data will be used in the analysis zone of the analyzer. Note, however, that
gathered. The test should be carefully designed to ensure the
the actual standard deviation in static stability tests might be
user’s requirements are met. influenced by the composition or mass of the coal being
examined or analyzer factors, such as the strength of the
5.3 The procedures defined in this guide can be used to
radioactive sources used by the analyzer or condition of
estimate the accuracy and precision of an online analyzer, (1)
analyzer electronic components.
to conduct acceptance testing following installation and (2) to
6.2.2 It is essential that the length of the analysis period be
monitor the accuracy and precision (a) during routine use
defined, (for example, one minute, two minutes, or five
(quality control), (b) when significant changes are made to the
minutes) and be constant in the static stability test. The
analyzer, and (c) when a significant change in the coal being
standard deviation resulting from the static stability test de-
analyzed occurs (e.g., a different seam at a mine, or a new coal
creases as the length of the analysis period increases.
source at a power plant).These procedures can also be used for
calibration purposes.
6.3 Comparison of Analyzer System to Reference System
Measurements:
6. Selection and Conduct of Performance Evaluations
6.3.1 Once an analyzer installation has been completed and
6.1 Introduction:
calibration adjustments have been made, the analyzer owner
6.1.1 Several techniques can be used to evaluate the perfor-
may require acceptance testing. Also, the analyzer owner may
mance of an online analyzer. These techniques provide data
decide to relocate the analyzer. In these cases, comparison
that can be evaluated by using the graphical and statistical
tests–that is, to compare the analyzer system results to conven-
methods described in Section 7 of this guide.
tional sampling and analysis techniques–will provide the user
6.1.2 At the time of installation, all of the graphical and
calibration verification data and/or data that could be used for
numerical methods outlined in this guide may prove useful. On
recalibration of the analyzer.
a routine basis, conducting any of the instrument stability
6.3.2 Sinceperformanceevaluationsusuallyconsistof30or
checks and comparative evaluations that do not disrupt normal
more comparisons, with each of these lasting from 30 minutes
operations may prove useful. Control charts may be applied to
to three hours, these comparisons may be conducted in a batch
all the performance measures that are gathered on a routine
over several hours or days, or continuously throughout the
basis, including mean analysis value of reference material,
operational life of the analyzer system.
RMSD, etc.
6.3.3 If two independent conventional coal-sampling and
6.1.3 Whenever there is a major change to the operating
laboratory analysis measurements can be made from each of a
parameters, the configuration, the calibration, the processes, or
series of batches of coal interrogated by the analyzer, the
the hardware associated with the analyzer or the reference
Latent Variable Model (LVM) can be used to provide unbiased
system, the user may wish to perform comparative tests. In
estimates of the measurement precision of the analyzer and of
addition to comparative tests, standardization or static tests, or
the conventional sampling and analysis systems.
both, as recommended by the online analyzer manufacturer,
may be helpful. 6.3.4 Any two series of measurements are independent if
6.1.4 Changes in coal characteristics may also impact ana- their measurement errors are uncorrelated. Correlation of
lyzer performance. Particle size, source of coal, mining measurement errors can be avoided and independence assured
techniques, and degree of preparation, which if changed from by use of a true random selection of physical increments or
previous test periods and which are not in the analyzer samples of material or by using different schemes and equip-
calibration database, may affect analyzer precision and accu- ment for collection, preparation, and laboratory analysis of the
racy. samples, or both. A complete treatment of the subject of
D6543 − 15
independence of measurements and the various means of
assuring independence is beyond the scope of this guide.
6.4 Sampling Considerations:
6.4.1 Selection of Appropriate Sampling and Sample Prepa-
ration Methods—Decisions regarding sample collection should
be governed by Practices D2234/D2234M and D7430 as
appropriate. The method to be used for sample preparation
should be determined before the beginning of increment
collection. Sample preparation techniques should remain con-
sistent (see Practice D2013). Before installation of the
analyzer, consideration should be given to the ability to obtain
representative samples for comparison to analyzer measure-
ments and the regimen for sample handling and analysis. For
the use of mechanical sampling systems, inspection (see
Practice D7430, Part C) and bias testing (see Practice D7430,
Part D) are good methods for evaluation of the system’s
suitability for the test.
6.4.2 Selection of Reference Sample Point(s):
6.4.2.1 Comparative tests can be used to evaluate the
performance of either the analyzer itself or the “analyzer
FIG. 2 Analyzer on Secondary Reject—Three-Stage Mechanical
Sampling
system” (consisting of the analyzer and the sampling system
that feeds it). The comparative evaluations of the analyzer
system can be used to determine the ability of the analyzer
system to measure the characteristics of the main coal stream.
The selection of the reference system sample point(s) deter-
mines whether the comparative tests will assess the analyzer or
the analyzer system.
6.4.2.2 The most direct and practical two-instrument test,
when the analyzer is fed the secondary reject of a mechanical
sampling system, uses the final save to compare directly to the
analyzer. A manual or mechanical sample collected from the
analyzer discharge may provide an independent sample, which
may be used to assess the performance of the analyzer (see
Figs. 1-3).
FIG. 3 Analyzer on Secondary Reject—Two-Stage Mechanical
Sampling
requires more than one set of comparative data might incor-
porate a series of samples (stopped belt or full stream cut)
FIG. 1 Key to Schematics
collected from the analyzer discharge or the secondary reject
stream, as well. In the relatively rare circumstances in which
6.4.2.3 There are instances when there is no save sample the analyzer discharge feeds two additional stages of sampling,
(see Fig. 4) associated with the system feeding the analyzer. In the tertiary save is recommended for two-instrument and bias
this case, it is possible to construct a test with several testing, and a stopped belt or full stream cut of the secondary
comparisons by collecting separate samples from the analyzer or tertiary rejects of the analyzer discharge may be used as a
feed and discharge. third instrument. Practical considerations of increment collec-
6.4.2.4 In some instances, the discharge of the analyzer may tion at the secondary reject should be balanced with consider-
be fed to further stages of mechanical sampling.Asingle stage ations of sampling variances introduced by crushing and
of sampling downstream of the analyzer is most common (see tertiary sampling. For two instruments to be independent of
Fig. 5). In this case, the secondary save will provide a each other, one or both instruments must interrogate the stream
convenient comparison sample. A test of such a system that of interest without changing the characteristics of the stream.
D6543 − 15
FIG. 6 Analyzer Distinct from Reference
rations. In the case of flow-through analyzers that require a
sample, the independence of systems is obtained in a case in
which the primary coal stream is sampled by one instrument
beforebeingsampledbyanotherinstrument(seeFig.6).Inthis
case, the two systems may be evaluated by comparing the
FIG. 4 Single-Stage Mechanica
...

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: D6543 − 14b D6543 − 15
Standard Guide to
the Evaluation of Measurements Made by Online Coal
Analyzers
This standard is issued under the fixed designation D6543; 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
1.1 This guide provides techniques to be used for the evaluation of the measurement performance of online coal analyzers.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D121 Terminology of Coal and Coke
D2013 Practice for Preparing Coal Samples for Analysis
D2234/D2234M Practice for Collection of a Gross Sample of Coal
D6518 Practice for Bias Testing a Mechanical Coal Sampling System (Withdrawn 2008)
D7430 Practice for Mechanical Sampling of Coal
E178 Practice for Dealing With Outlying Observations
3. Terminology
3.1 Definitions—For additional definitions of terms used in this standard, refer to Terminology D121.
3.2 Definitions:Definitions of Terms Specific to This Standard:
3.2.1 analyzer system, n—a coal quality measurement system which includes an online coal analyzer and which may include
one or more stages of a coal-sampling system.
3.2.2 calibration, n—mathematical modeling of analyzer and comparative coal sampling and analysis data. Factors from the
model are used in the online analyzer control software.
3.2.3 full-stream analyzer, n—an analyzer system that interrogates the coal on a process belt.
3.2.4 Latent Variable Model, n—a mathematical model that can estimate each system’s precision, when the analyzer is
compared to two independent reference systems.
3.2.5 online analyzer, n—an analytical tool consisting of an instrument and systems, which together provide measurements, or
estimates, or both, of coal quality parameters.
3.2.6 outlier, n—an extreme value that statistical tests indicate to be far enough from other results in a population under
consideration to cause suspicion that the value is not a member of the population.
3.2.7 reference material, n—material of stable composition that may be used to generate static analyzer measurements.
3.2.8 reference system, n—a measurement system used to measure the characteristics of a lot of coal that are also measured by
an online analyzer, and against which the online analyzer measurements are compared.
3.2.9 sample stream analyzer, n—an analyzer system that is fed a save or reject stream from a sampling system.
3.2.10 standardization, n—calibration of an instrument to a reference material using static stability measurements.
This guide is under the jurisdiction of ASTM Committee D05 on Coal and Coke and is the direct responsibility of Subcommittee D05.23 on Sampling.
Current edition approved Sept. 1, 2014Jan. 1, 2015. Published October 2014January 2015. Originally approved in 2000. Last previous edition approved in 2014 as
D6543-14a.-14b. DOI: 10.1520/D6543-14b.10.1520/D6543-15.
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’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6543 − 15
3.2.11 static stability, n—an estimate of the measurement precision of an instrument obtained on material that is not moving.
The estimate normally is expressed as the standard deviation and average of the measurements for a given period of time.
3.2.12 synchronization error, n—an error that occurs from comparing measurements made by an online analyzer and a reference
system that are not measuring exactly the same lot because of temporal and/or spatial offsets.
4. Summary of Guide
4.1 This guide describes how to measure performance of an online analyzer using comparative measurements. The performance
evaluation consists of a paired comparison of analyses from a reference method using ASTM sampling, sample preparation, and
analysis methods for several lots of coal with the analyses from the online analyzer for the same lots of coal. The data resulting
from the comparative test may be evaluated using graphical and statistical techniques outlined below.
4.2 Various techniques are recommended by online analyzer manufacturers for standardization or static testing. These
techniques are useful for establishing a benchmark before conducting a comparative test. These techniques may also be used as
diagnostic tests in accordance with methods recommended by online analyzer manufacturers and graphical and statistical
techniques included in this guide.
5. Significance and Use
5.1 Online analyzers are used to provide quality data on lots of coal. The resulting quality data are used as a production tool
or for some contractual application. This guide provides the means of evaluating the analyzer system and the data produced.
5.2 Become familiar with the document’s terminology and layout. The section on test design and data collection will provide
the means by which all the analysis data will be gathered. The test should be carefully designed to ensure the user’s requirements
are met.
5.3 The procedures defined in this guide can be used to estimate the accuracy and precision of an online analyzer, (1) to conduct
acceptance testing following installation and (2) to monitor the accuracy and precision (a) during routine use (quality control), (b)
when significant changes are made to the analyzer, and (c) when a significant change in the coal being analyzed occurs (e.g., a
different seam at a mine, or a new coal source at a power plant). These procedures can also be used for calibration purposes.
6. Selection and Conduct of Performance Evaluations
6.1 Introduction:
6.1.1 Several techniques can be used to evaluate the performance of an online analyzer. These techniques provide data that can
be evaluated by using the graphical and statistical methods described in Section 7 of this guide.
6.1.2 At the time of installation, all of the graphical and numerical methods outlined in this guide may prove useful. On a routine
basis, conducting any of the instrument stability checks and comparative evaluations that do not disrupt normal operations may
prove useful. Control charts may be applied to all the performance measures that are gathered on a routine basis, including mean
analysis value of reference material, RMSD, etc.
6.1.3 Whenever there is a major change to the operating parameters, the configuration, the calibration, the processes, or the
hardware associated with the analyzer or the reference system, the user may wish to perform comparative tests. In addition to
comparative tests, standardization or static tests, or both, as recommended by the online analyzer manufacturer, may be helpful.
6.1.4 Changes in coal characteristics may also impact analyzer performance. Particle size, source of coal, mining techniques,
and degree of preparation, which if changed from previous test periods and which are not in the analyzer calibration database, may
affect analyzer precision and accuracy.
6.1.5 Additional changes which could merit performance testing include a change in the material or width of the conveyor, or
coal flow rates (in the case of full-flow analyzers).
6.2 Static Stability Measurements for Baseline Assessment—A reference material may be used to provide a baseline assessment
of static measurement precision. The reference material may be used to compare current mean and standard deviation values with
mean and standard deviation values, previously collected in the same manner. The resulting comparative data may help determine
whether any apparent decline in analyzer dynamic performance may be attributed to a change in the operating characteristics of
the analyzer, in the absence of the influence of sampling, preparation, and analysis.
6.2.1 The results of this evaluation can indicate whether analyzer precision has significantly degraded or whether a bias may
have occurred. If so, it may be possible to adjust the analyzer to restore initial performance. If the user wishes only to measure
current static stability, any available coal may be used in the analysis zone of the analyzer. Note, however, that the actual standard
deviation in static stability tests might be influenced by the composition or mass of the coal being examined or analyzer factors,
such as the strength of the radioactive sources used by the analyzer or condition of analyzer electronic components.
6.2.2 It is essential that the length of the analysis period be defined, (for example, one minute, two minutes, or five minutes)
and be constant in the static stability test. The standard deviation resulting from the static stability test decreases as the length of
the analysis period increases.
6.3 Comparison of Analyzer System to Reference System Measurements:
D6543 − 15
6.3.1 Once an analyzer installation has been completed and calibration adjustments have been made, the analyzer owner may
require acceptance testing. Also, the analyzer owner may decide to relocate the analyzer. In these cases, comparison tests–that is,
to compare the analyzer system results to conventional sampling and analysis techniques–will provide the user calibration
verification data and/or data that could be used for recalibration of the analyzer.
6.3.2 Since performance evaluations usually consist of 30 or more comparisons, with each of these lasting from 30 minutes to
three hours, these comparisons may be conducted in a batch over several hours or days, or continuously throughout the operational
life of the analyzer system.
6.3.3 If two independent conventional coal-sampling and laboratory analysis measurements can be made from each of a series
of batches of coal interrogated by the analyzer, the Latent Variable Model (LVM) can be used to provide unbiased estimates of
the measurement precision of the analyzer and of the conventional sampling and analysis systems.
6.3.4 Any two series of measurements are independent if their measurement errors are uncorrelated. Correlation of measurement
errors can be avoided and independence assured by use of a true random selection of physical increments or samples of material
or by using different schemes and equipment for collection, preparation, and laboratory analysis of the samples, or both. A
complete treatment of the subject of independence of measurements and the various means of assuring independence is beyond
the scope of this guide.
6.4 Sampling Considerations:
6.4.1 Selection of Appropriate Sampling and Sample Preparation Methods—Decisions regarding sample collection should be
governed by Practices D2234/D2234M and D7430 as appropriate. The method to be used for sample preparation should be
determined before the beginning of increment collection. Sample preparation techniques should remain consistent (see Practice
D2013). Before installation of the analyzer, consideration should be given to the ability to obtain representative samples for
comparison to analyzer measurements and the regimen for sample handling and analysis. For the use of mechanical sampling
systems, inspection (see Practice D7430, Part C) and bias testing (see Practice D7430, Part D) are good methods for evaluation
of the system’s suitability for the test.
6.4.2 Selection of Reference Sample Point(s):
6.4.2.1 Comparative tests can be used to evaluate the performance of either the analyzer itself or the “analyzer system”
(consisting of the analyzer and the sampling system that feeds it). The comparative evaluations of the analyzer system can be used
to determine the ability of the analyzer system to measure the characteristics of the main coal stream. The selection of the reference
system sample point(s) determines whether the comparative tests will assess the analyzer or the analyzer system.
6.4.2.2 The most direct and practical two-instrument test, when the analyzer is fed the secondary reject of a mechanical
sampling system, uses the final save to compare directly to the analyzer. A manual or mechanical sample collected from the
analyzer discharge may provide an independent sample, which may be used to assess the performance of the analyzer (see Figs.
1-3).
FIG. 1 Key to Schematics
6.4.2.3 There are instances when there is no save sample (see Fig. 4) associated with the system feeding the analyzer. In this
case, it is possible to construct a test with several comparisons by collecting separate samples from the analyzer feed and discharge.
6.4.2.4 In some instances, the discharge of the analyzer may be fed to further stages of mechanical sampling. A single stage of
sampling downstream of the analyzer is most common (see Fig. 5). In this case, the secondary save will provide a convenient
comparison sample. A test of such a system that requires more than one set of comparative data might incorporate a series of
samples (stopped belt or full stream cut) collected from the analyzer discharge or the secondary reject stream, as well. In the
relatively rare circumstances in which the analyzer discharge feeds two additional stages of sampling, the tertiary save is
recommended for two-instrument and bias testing, and a stopped belt or full stream cut of the secondary or tertiary rejects of the
analyzer discharge may be used as a third instrument. Practical considerations of increment collection at the secondary reject
should be balanced with considerations of sampling variances introduced by crushing and tertiary sampling. For two instruments
to be independent of each other, one or both instruments must interrogate the stream of interest without changing the characteristics
of the stream. This may be true in some through-belt noncontacting configurations. In the case of flow-through analyzers that
D6543 − 15
FIG. 2 Analyzer on Secondary Reject—Three-Stage M
...