United States Office of Air Quality "{K/
Environmental Protection Planning and Standards January
Agency Research Triangle Park NC 27711
Stationary Source Compliance Series
A Compilation
of Opacity
Monitor
Performance
Audit Results
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EPA-340/1-83-011
A Compilation of Opacity Monitor
Performance Audit Results
Prepared by:
Steve Plaisance
Entropy Environmentalists, Inc.
Research Triangle Park, North Carolina
Prepared for:
Darryl von Lehmden
and
Thomas Logan
Quality Assurance Division
United States Environmental Protection Agency
QAD Contract No. 68-02-3431
and
Louis R. Paley
Stationary Source Compliance Division
United States Environmental Protection Agency
SSCD Contract No. 68-01 -6317
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air Quality Planning and Standards
Stationary Source Compliance Division
Washington, D.C. 20460
January 1983 ,t ^ s
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The Stationary Source Compliance series of reports is issued by the
Office of Air Quality Planning and Standards, U. S Environmental
Protection Agency, to assist Regional Offices in activities related to
compliance with implementation plans, new source emission standards,
and hazardous emission standards to be developed under the dean Air
Act. Copies of Stationary Source Compliance Reports are available -
as supplies permit - from Library Services, U.S. Environmental
Protection Agency, MD-35, Research triangle Park, North Carolina
27711, or may be obtained, for a nominal cost, from the National
Technical Information Service, 5285 Port Royal Road, Springfield,
Virginia 22151.
This report has been reviewed by the Office of Air Quality Planning
and Standards, U.S. Environmental Protection Agency, and approved for
publication as received from Entropy Environmentalists, Inc. Approval
does not signify that the contents necessarily reflect the views and
policies of the U.S. Environmental Protection Agency, nor does mention
of trade names or commercial products constitute endorsement or
recommendation for use.
ii
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ABSTRACT
Opacity monitor performance audit procedures and devices have been
developed and field tested on 93 opacity monitors * The results of this
test program indicate that opacity monitoring systems achieve high levels
of availability, and are capable of providing accurate emissions data. The
results also show that problems impacting data quality are generally
limited to monitor miscalibration and/or misadjustment, as well as improper
or inadequate operating and maintenance practices. It is believed that
improved monitor performance and data reliability can be achieved with
additional training of monitor operators and more frequent performance
audits.
This document describes the audit program for continuous emission
monitors (CEMs) of effluent opacity. Detailed explanations of the audit
methodology, monitor analyses, and analytical criteria are included, and
both criteria- and monitor-specific results of installed opacity monitor
audits are delineated. Finally, conclusions are drawn as to the adequacy
of monitor performance and data reliability, and recommendations are
offered that can optimize opacity monitoring system performance.
iii
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II. PERFORMANCE AUDIT PROGRAM
Audit Program Description
Performance audits of 93 opacity monitors were conducted at 41 sources
in EPA Regions IV, V, and VII through July 1982. All monitors were located
at coal-fired steam generators, with the exception of one that was located
at a petroleum refinery catalytic regenerator. These test sites were
selected according to the following audit criteria:
The test site had at least one of the four representative
monitor types in current use (Lear Siegler, Contraves Goerz,
Dynatron, Esterline Angus).
The monitor had been in operation for a minimum of one year.
The monitor had undergone a PST that indicated initial
compliance with Performance Specification 1, Appendix B,
40 CFR 60.
The opacity monitor audit program was designed to provide accurate,
reliable analyses of monitor performance through a simple, quick field test
procedure which can be performed by a single technician with a basic
understanding of transmissometry. Equipment necessary for a typical audit
includes a specialized retroreflector for the specific monitor being tested
to simulate clear stack conditions. In addition, three neutral density
filters, traceable to the National Bureau of Standards (NBS) , are included
to evaluate both the linearity and the calibration error of the monitor.
All of the necessary equipment can be transported in a small suitcase.
Audit Methodology
Opacity monitor field audits consist of two sequential procedures: (1)
a general information survey and (2) the site monitor audit. The general
information survey, typically conducted prior to the actual site visit,
serves to gather information required to tailor the audit procedures and
equipment to the specific source and monitor. This information includes:
1. Source identification, location, fuel used, emission control
device(s) (before and after the monitor).
2. Opacity monitor manufacturer, model and serial numbers, dates
of installation and certification (PST), stack diameters at
monitor location and exit, proximity to upstream or downstream
flow disturbances, types of opacity data recording equipment
and recording intervals.
3. Date of most recent opacity monitor calibration and type of
calibration (off-stack using neutral density filters, or
on-stack during clear-stack conditions) , recalibration
criteria (zero/span error or scheduled recalibration), time
interval between check/change of air purge filters, between
check/change of optical surfaces, or between zero/span
adjustment.
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The field audit procedures are used to determine whether the monitor
has been properly operated and whether the monitor accuracy and calibration
are of sufficient quality to provide useful opacity data. Although these
procedures may differ slightly in their order for each type of monitor,
they all include the following three basic analyses:
1. Monitor Component Analysis,
a. The fault lamp indicators on the monitor's control panel are
checked to determine whether the monitor is operating within
the manufacturer's prescribed limits.
b. The stack exit diameter and monitor pathlength are determined
to verify the accuracy of the monitor's preset stack exit
opacity correction factor.
c. Various internal electronic checks are performed using the
controls in the monitor's control unit to further verify the
operational status of the monitor.
d. The control panel meter and chart recorder responses are
compared to the monitor's internal span value, in order to
determine the accuracy of the control panel meter and internal
zero and span functions.
2. Monitor Maintenance Analysis,
The optical alignment and dust accumulation on optical
surfaces are checked to determine the adequacy of the monitor
mounting and maintenance frequency.
3. Calibration B-ror Analysis,
The calibration error and linearity of the monitor are checked
using neutral density filters.
The Lear Siegler, Esterline Angus, and Contraves Goer z monitors
require that an audit device with an adjustable retroreflector be mounted
on the transceiver to simulate clear stack conditions. Neutral density
filters are then inserted into the audit device to determine the
calibration/accuracy of the monitor at three different opacity levels. For
the Dynatron opacity monitor, the audit device neutral density filters must
be inserted in front of the monitor's retroreflector. This methodology
provides an incremental calibration check, because the filter opacity is
combined with the effluent opacity.
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Audit Procedures and Terminology
Each opacity monitor field audit comprises up to 10 specific analyses
which encompass the monitor's accuracy, precision, and the quality of
monitor operation and maintenance practices. These procedures and their
associated terminology are detailed as follows:
Fault Lamp Analysis. The transceiver unit of a typical opacity
monitor has several fault monitors that warn of monitor system malfunctions
and/or impending conditions of excessive opacity. Monitor fault lamps are
indicative of a variety of conditions, depending on the manufacturer, but
most units use fault lamps to monitor the intensity of the optical beam,
the quantity of dust on monitor optical surfaces, the status of internal
circuitry that maintains monitor calibration, and/or the magnitude and rate
of increase of opacity. In general, a fault lamp error exists if, at the
time of a performance audit, any of the fault lamps are illuminated.
However , the absence of illuminated fault lamps does not preclude
malfunctions in the fault lamp circuits or the lamp bulbs.
Automatic Gain Control (AGO) Circuit Analysis. Lear Siegler opacity
monitors employ an AGC circuit to compensate electronically for reductions
in the optical beam intensity resulting from power supply fluctuations or
normal bulb deterioration. This compensation prevents beam intensity
variations from being interpreted as variations in measured opacity. Thus,
a fault condition exists when a Lear Siegler monitor's AGC circuit is not
functional, and is indicated when the AGC lamp is not lit. However, an AGC
circuit fault does not necessarily diminish the accuracy of opacity
measurements, provided that the reference signal value is within the
specified range.
Monitor Alignment Analysis. The optical alignment of the
transceiver/retroreflector system is critical in maintaining accurate
opacity measurements. Misalignment of the beam can cause erroneously high
opacity readings, because a significant portion of the measurement beam is
not returned to the transceiver. Most opacity monitor manufacturers
include provisions for an optical alignment check, as either a standard
feature or an option. Monitor alignment errors are indicated by an
off-center beam image on the transceiver and/or retrore flee tor.
Stack Exit Correlation Analysis. Typically, the cross-stack optical
pathlength of the installed opacity monitor is not equal to the diameter of
the stack exit. To obtain a true stack exit opacity value, the measured
opacity at the monitor location is corrected to stack exit conditions
through the use of a pathlength correction factor. The stack exit
correlation error is the percent error of the pathlength correction factor,
as preset by the manufacturer, relative to a pathlength correction factor
calculated through the use of actual measurements, blueprints, etc.
Control Panel Meter Analysis. Most opacity monitors have a panel
meter located on their control or transceiver units to monitor opacity
readings or to adjust an internal monitor parameter. The control panel
meter correction factor is the meter readings compared to the specified
opacity value for the internal span filter.
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Reference Signal Analysis. The Lear Siegler monitor reference signal
is an internal monitor electrical signal output that indicates the
electronic alignment of the transceiver circuitry (usually 20 ma). The
reference signal error is the percentage difference between the measured
current value of the signal and the specified 20-ma value.
Internal Zero and Span Analysis. The zero and span errors are the
percentage difference between the internal reference filter opacities that
the monitoring system should record and those opacity values actually
displayed on the chart recorder. These errors occur due to one or a
combination of reasons: (a) the values for the internal zero and span
functions are wrong, (b) the internal electronics responding to the zero
and span functions are not working properly, (c) the signal from the
transceiver to the chart recorder is being altered, and (d) the chart
recorder is not displaying the incoming signal correctly.
Zero Compensation Analysis. The zero compensation circuit of the Lear
Siegler monitor automatically adjusts the monitor's zero to compensate for
dust accumulation on the transceiver's optical surfaces. The zero
compensation analysis is based on recording the zero compensation before
and after cleaning the transceiver and retro-reflector optical surfaces.
Optical Surface Dust Accumulation Analysis. The optical surface dust
accumulation analysis determines the amount of dust (measured in terms of
percent opacity) found on the optical surfaces, based on the reduction in
opacity before and after cleaning of the optical surfaces. To obtain a
reliable assessment, this audit analysis should be performed when the stack
opacity is relatively constant.
Calibration Error Analysis. This analysis involves comparison of the
monitor responses to the known opacity values for a series of three
reference neutral density filters (as modified in opacity value by the
optical pathlength correction factor). The calibration of the reference
filters used in this analysis is traceable to the NBS.
Audit Criteria
Specific criteria have been developed for the determination of opacity
monitor performance based on (1) Performance Specification 1, Appendix B,
40 CFR 60, (2) manufacturer's recommendations, and (3) extensive practical
experience. For the previous analytical procedures, these criteria are:
Fault Lamp Analysis. A fault lamp error is indicated when one or more
of the control unit fault lamps are illuminated. Under performance audit
conditions, these lamps provide an indication of monitor systems and
parameters that may be out-of-specification prior to the audit, thereby
signifying the level of monitor operation and maintenance.
Automatic Gain Control (AGC) Circuit Analysis. A Lear Siegler AGC
circuit error occurs when the AGC circuit is not operating. The AGC LED,
located on the transceiver head, is illuminated when the AGC circuit is
operating.
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Monitor Alignment Analysis. The optical beam path should be properly
aligned as indicated by checking the centering of the beam image on the
transceiver and/or r etrore flee tor .
Stack Exit Correlation Analysis. The percent error of the optical
pathlength correction factor, as preset by the monitor manufacturer,
relative to that calculated from actual measurements, should be no greater
than +2 percent.
Control Panel Meter Analysis. The control panel meter correction
factor, based on a comparison of opacity values between the meter and that
of the internal span filter, should fall within the range of 0.98 to 1.02,
or +2 percent opacity (differences of more than 10 percent opacity may be
indicative of other monitor problems) .
Reference Signal Analysis. The Lear Siegler reference signal error,
as indicated by the percentage difference in the internal reference signal
value and the manufacturer's specified value of 20 ma, should not exceed
+ 10 percent of the specified value.
Internal Zero and Span Analysis. Internal zero and span errors, based
on comparing the monitor internal filter opacity values with those
indicated by the opacity recorder, should not exceed +2 percent opacity.
Zero Compensation Analysis. The zero compensation analysis, based on
a comparison of zero compensations before and after cleaning of monitor
optics, should result in an automatic zero adjustment range of +0.018
optical density (not in excess of +4 percent opacity) The zero
compensation should approach 0.000 optical density after cleaning.
Optical Surface Dust Accumulation Analysis. The optical surface dust
accumulation, based on the difference in opacity readings before and after
cleaning of monitor optics, should not exceed 4 percent opacity.
Calibration Error Analysis. Transmissometer calibration error, based
on the sum of the absolute value of the mean difference and 95 percent
confidence interval observed for the differences in opacity indicated by
the monitor and that of the given reference neutral density filters, should
be no greater than 3 percent opacity.
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III. SUMMARY AND DISCUSSION OF AUDIT RESULTS
Opacity monitor audit results are summarized and discussed in this
section for the four representative types of monitors evaluated. Table 1
summarizes results of the audit analyses of the four monitors. Figure 1
illustrates the relationship between actual and measured opacity for all
monitor types, and Figures 2 through 5 illustrate the same relationship for
each type of monitor tested.
Results of Criteria-Specific Analyses
General Operation and Maintenance Survey. At the initiation of the
opacity monitor field audit program, all of the monitors were believed to
be functioning properly. However, of the 93 monitors audited, only 89 were
fully operational. Monitor availability, as determined by reviewing the
previous month's data, was 100 percent for 69 of the 93 monitors, and the
average monitor availability was approximately 95 percent.
The general audit survey includes a variety of factors affecting
monitor operation and maintenance (e.g., the accessibility for maintenance,
the supply of spare parts, etc.). In general, these factors had little
correlation with monitor performance. However, one factor of significant
importance was whether the monitor maintenance was performed by plant
personnel or by a monitor-servicing contractor. Nearly all (six of seven)
of the monitors serviced by monitor-servicing contractors had calibration
errors of _<3 percent opacity. In contrast, monitors serviced by site
personnel often lacked necessary maintenance, and two sources were
identified at which monitor manufacturer's specifications for maintenance
were not followed .
During the audit program, 30 opacity monitors that were installed in
exhaust ducts transporting effluent streams to a common exhaust stack were
audited. None of these common stacks had an installed opacity monitor . To
determine the stack exit opacity, the source combined the duct opacities
measured by the respective monitors without weighting them according to
duct flowrate . In addition, a few of these sources simply arithmetically-
averaged the duct opacities to obtain a stack exit opacity. Thus, in cases
where the duct flowrates were unequal , the total opacities measured for
combining duct systems were determined incorrectly.
Fault Lamp Analysis. The fault lamps provide a good indication of the
current status of the monitoring system operation and maintenance,
particularly with reference to the optical beam intensity, optical system
dust accumulation, or a zero/span malfunction. The monitor parameter
indicated by a fault lamp is considered to be "out of specification" if the
control unit lamp is illuminated. Of the 93 monitors audited,
approximately 4 percent of the total were found to have one or more
illuminated fault lamps. In addition, these same monitors had calibration
errors in excess of 10 percent, thereby indicating a positive correlation
between the fault lamp status and the reliability of measured opacity.
Automatic Gain Control (AGO Circuit Analysis. The status of the AGC
circuit (anployed on the Lear Siegler monitor only) is indicative of the
monitor's ability to compensate electronically for reductions in the
optical beam intensity resulting from fluctuations in the lamp electrical
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TABLE 1. OPACITY MONITOR AUDIT RESULTS
AUDIT
ANALYSES
Number of Monitors Audited
MONITOR COMPONENT ANALYSIS
Fault Lamps
AGC Circuit
Monitor Alignment
Stack Exit Correlation Error
Panel Meter Status
Reference Signal Error
Internal Span Error
Internal Zero Error
MONITOR MAINTENANCE ANALYSIS
Zero Compensation Factor
Optical Eust Accunulc^ion
Calibration Error Analysis :^
Low Range (8.5% Opacity)
Midrange (18.5% Opacity)
High Range (42.5% Opacity)
LEAR
Number
Within
Specs.
SIEGLER
Number
Out of
Specs.
58
56
57
55
51
0
54
44
53
47
41
50
49
46
2
1
0
7
55 4
1
11
2
8
12
5
7
9
CONTRA VES GOERZ DYNATRON
Number Number Number Number
Within Out of Within Out of
Specs. Specs. Specs. Specs.
27
27
NA3
26
26
22
NA
22
25
NA .
22
25
22
19
0
NA
0
1
5
NA
5
2
NA
3
2
5
8
3
NA
3
2
4
NA
3
3
NA
3
1
1
0
5
2
NA
2
3
0
NA
1
1
NA
1
3
3
4
ESTERLINE ANGUS
Number Number % Total Number
Within Out of Monitors Tested
Specs. Specs. Out of Specs.
3
3
NA
2
3
2
NA
3
3
NA
3
3
3
2
0
NA
1
0
1
NA
0
0
NA
0
0
0
1
4
2
3
12
69
2
19
6
15
19
11
17
25
See Section II of this report for audit methodology, definition of terms, and audit criteria.
The calibration error analysis for the Dynatron monitors utilized different neutral density filters:
Low Range = 17.0$ Opacity, Midrange = 56.5% Opacity, and High Range = 81.0% Opacity.
Not Applicable
Lear Siegler panel meter readings of opacity were generally accurate, but values for optical density
and circuit current were typically erroneous.
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70
20 30 40
Actual Opacity (% Opacity)
Figure 1. Observed Opacity Responses for All
Audited Monitors: 8.9 Monitors
12
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70
60
•H
O
a
o
W
c
o
CO
0)
o
(0
QJ
M
3
CO
(1)
Actual Opacity (% Opacity)
Figure 2. Observed Opacity Responses for 58 Lear Siegler
Monitors
13
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•H
O
td
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O
(U
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c
o
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•p
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40.
10-
Range of Measured Responses
Average'Measured Responses
/
±3% Opacity
Error Band
Expected Responses
i I I i | i I i i
I l i I | i i i i
IMIIIIII
10 20 30 40
Actual Opacity (% Opacity)
Figure 3, Observed Opacity Responses for 27
Contraves Goerz Monitors
50
14
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100
80
-P
•H
O
(0
ft
O
Oft
4J
•H
O
0)
M
d
en
-------
70
60
50
4J
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(0
Ck
o
df>
•H
O
T)
(U
M
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en
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40
20
10
Range of Measured Responses
Average Measured Responses —
+3% Opacity
Error Band
Expected Responses
M T I I [ l t i i i l i | i i l i 11 i i i | i M i | i i i i i i i i i i
0 10 20 30 40
Actual Opacity (% Opacity)
50
Figure 5. Observed Opacity Responses for 3 Esterline Ang\
Monitors
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supply and/or deterioration of the lamp bulb. The AGC circuit is
considered to be "out of specification" if the circuit is not operating, as
indicated by an LED on the Lear Siegler transceiver. Of the 58 monitors
evaluated, only one monitor (approximately 2 percent of the total) was
found to have an inoperative AGC circuit.
Monitor Alignment Analysis. The monitor alignment analysis indicates
whether the optical beam path across the effluent stream is centered on the
measurement r etr ore flee tor , with "out of specification" conditions being
indicated by an off-center beam path. Improper alignment was found in
three of 89 monitors audited, representing about 3 percent of the total.
In addition, two of these monitors (Dynatron) were out-of-calibration, and
the source indicated that attempts at proper alignment resulted in the loss
of monitor zeroing capability. During o ff-stack calibration , however, an
alternative alignment was devised, but this alignment failed to correct the
zero calibration problem when the monitor was installed on the stack,
thereby indicating that such problems may require the attention of a
monitor service specialist. Finally, three Lear Siegler monitors had
faulty alignment sights, and therefore, were not included in the tabulated
audit results.
Stack Exit Correlation Analysis. The stack exit correlation analysis
evaluates the pathlength correction factor which has an exponential impact
on the monitor opacity reading. The audit results indicate that the most
common error in computing the monitor optical pathlength was the use of the
flange-to-flange distance, rather than the stack/duct inside diameter.
Approximately 12 percent of the monitors audited had incorrect pathlength
correction factors. However, the data obtained for these monitors can be
used, provided that the erroneous opacity readings are mathematically
corrected by using the proper pachlength correction factor.
Panel Meter Analysis. The panel meter analysis serves to evaluate the
accuracy of the panel meter readings of opacity, optical density, and (on
Lear Siegler monitors only) reference circuit current values. The panel
meter is considered to be "out of specification" if any of the meter
readings vary by more than 2 percent of the true value. Although 61 of the
monitors audited (about 69 percent of the total) exhibited faulty panel
meter readings, 55 of these units were Lear Siegler monitors which
accuractely indicated opacity, but were inaccurate in their readings of
optical density and/or monitor circuit current. In addition, zero and span
function adjustments were made on five monitors using inaccurate panel
meter readings. In general, the audit results indicated that chart
recorder readings of opacity, optical density, and monitor circuit current
should be used in monitor calibration and adjustment. However, seven
monitors (8 percent of the total) were found to have incorrect chart
recorder readings.
Reference Signal Analysis. The reference signal analysis for the Lear
Siegler monitor serves as an internal verification of the beam intensity as
well as an indication of the status of the photo detector and its
associated electronics. The reference signal is considered to be "out of
specification" when it varies by more than -MO percent beyond the value
specified by the monitor manufacturer. Based on the audit data, all of the
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Lear Siegler monitors had reference signals within the recommended range,
with the exception of one unit. This monitor had an incorrectly calibrated
panel meter, and correction of this miscalibration resulted in a reference
signal reading within the manufacturer's recommended range.
Internal Zero and Span Analysis. The internal zero and span analysis
evaluates the monitor's ability to maintain calibration by automatically
adjusting its internal electronics to compensate for dust accumulation on
monitor optics. The zero and span are considered to be "out of
specification" when either of their errors exceed +2 percent opacity. The
audit results indicated no direct correlation between zero/span errors and
monitor miscalibration. Although 72 monitors had accurate zero/span
responses, 12 of these had calibration errors outside the specifications.
Likewise, of 17 monitors having zero/span errors exceeding the
specifications, only 10 had excessive calibration errors.
Procedural error was identified at two sources having seven monitors
in which the zero and span were adjusted without cleaning the monitor
optics. Because the zero mode is designed to simulate the amount of light
returned to the transceiver under clear stack conditions, any dust
accumulation on the transceiver window during the zero adjustment causes a
lesser amount of light to be returned to the detector, and thus, an
improper zero adjustment. However, the Lear Siegler monitor's zero
compensation circuit is automatically reset during the zero adjustment, and
the circuit will respond to the dirty optics as if they were clean. Thus,
the adverse impact of making zero adjustments without cleaning the monitor
optics depends on whether the monitor has a zero compensation function and
on its effectiveness, and may or may not bias the recorded opacity.
Zero Compensation Analysis. The zero compensation analysis evaluates
the extent to which the zero compensation circuitry of the Lear Siegler
monitor electronically nullifies the adverse effects of dust accumulation
on monitor optics. The zero compensation is considered to be "out of
specification" if the indicated value exceeds +0.018 optical density (4
percent opacity). The audit results indicated that the zero compensation
circuit values are an accurate measure of the amount of dust on the
transceiver optics, but give no indication of the dust accumulation on the
retroreflector . Eight (15 percent) of the 55 Lear Siegler monitors had
zero compensation values exceeding 4 percent opacity, and eleven monitors
incorrectly used the zero compensation value as an indication of dust
accumulation on the entire system optics. Thus, the Lear Siegler zero
compensation circuitry generally fulfills its intended purpose of
accounting for dirt on the transceiver optics.
Optical Dust Accumulation Analysis. The optical dust accumulation
analysis is a quantitative determination of the dust deposition on a
monitor's exposed optical surfaces. An "out of specification" dust
accumulation is indicated by a value in excess of 4 percent opacity. Of 85
monitors audited, 16 (19 percent of the total) had excessive dust on the
optical surfaces. The audit results indicated that dust deposition on
monitor optics is both site- and monitor-specific, with deposition
occurring at dissimilar, non-linear rates for transceiver and
retroreflector optics.
18
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Calibration Error Analysis. The calibration error analysis determines
the accuracy and linearity of the entire opacity monitoring system,
excluding retrore flee tor optics and monitor alignment. The calibration
error is considered to be "out of specification" if the difference between
the indicated opacity and that of the NBS neutral density filter employed
exceeds 3 percent opacity. In order to optimize the accuracy of the
calibration error analysis, all exposed monitor optics were cleaned prior
to calibration, and the optical pathlength correction factor preset by the
manufacturer was used to correct the audit filters for stack exit
conditions.
For all four types of monitors evaluated, the high range calibration
error was the most prevalent with 25 percent of the monitors having opacity
readings in excess of the specifications. Furthermore, the mid and low
range error analyses indicated corresponding reductions in calibration
error, with these values being determined as 17 percent and 11 percent,
respectively. Thus, a linear relationship between the magnitude of the
opacity and that of the calibration error was indicated wherein monitors
with lower range errors would not only have high range errors, but these
errors would be of a greater magnitude (see Figure 1). In general, the
monitors audited with calibration errors in excess of 3 percent opacity
were biased high. Poorly performing monitors tended to give falsely high
opacity readings, and, therefore, it is in the source's best interest to
calibrate and maintain opacity monitors properly.
Results of Monitor-Specific Analyses
Lear Siegler. The component analysis of 58 Lear Siegler opacity
monitors indicated significant problems with panel meter and internal span
errors. Although none of the monitors' panel meters were within
specifications, the erroneous readings were limited to values of optical
density and circuit current, with opacity readings of panel meters being
generally accurate. Internal span errors were present in 11 monitors (19
percent of the total) thereby, indicating either the presence of
significant quantities of dust on the transceiver system optics,
miscalibration of the monitor, or an incorrectly labeled internal span
filter.
An analysis of monitor maintenance indicated that dust accumulation on
system optics was a significant factor, with approximately 30 percent of
the Lear Siegler monitors having excessive dust accumulations. As a
further consequence of this dust accumulation, 17 percent of the monitors
had zero compensation values in excess of the specified value. In
addition, several of the sources indicated that they were unaware of the
specifications for the zero compensation value, thereby indicating their
lack of understanding of the role of the zero compensation as an indicator
of dust accumulation on the transceiver optics.
Monitor calibration was found to be generally accurate and linear,
with the greatest number of "out of specification" monitors resulting from
the high range calibration error analysis (9 monitors, or 16 percent of the
total). As Figure 2 illustrates, the Lear Siegler monitors tended to give
elevated opacity measurements, but typically not in excess of the 3 percent
19
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opacity error band based on average measured responses. However, the range
of measured opacities increased disproportionately with increases in the
actual opacity, thereby indicating that monitor accuracy deteriorated with
higher actual opacity.
Contraves Goerz. An analysis of the performance of 27 Contraves Goerz
monitors indicated that panel meter and internal span errors occurred in
about 20 percent of the monitors audited. Monitor maintenance, as
indicated by the optical dust accumulation, was generally satisfactory,
with only 3 units (about 12 percent of the total) having excessive dust
accumulations. Monitor calibration, as illustrated in Figure 3, was
adequate, with average low, medium, and high opacity values falling within
the +3 percent opacity error band. Contraves Goerz monitor opacity
measurements were typically higher than actual opacity values, and this
bias increased with higher actual opacity values.
Dynatron. Audits of 5 Dynatron opacity monitors yielded problems with
stack exit correlation factors in 60 percent of the monitors (3 units) .
Also, monitor alignment errors were found in 2 units, and these alignment
problems were not corrected. Fault lamp errors were encountered in 2
monitors, and were not previously repaired by the source because the
monitor control unit partially obscured view of the lamps.
Maintenance of Dynatron monitors, as indicated by dust accumulation on
monitor optics, was satisfactory, with only one monitor having excessive
dust on system optics. Figure 4 illustrates the very high bias found in
the calibration analysis, indicating severe inaccuracies in measured
opacity, particularly in the higher range of actual opacity values. In
fact, only 25 percent of the Eynatron units were found to be within the
acceptable range of accuracy for low and mid-range opacity values.
Moreover, monitor linearity was found to be deficient, with average
mid-range opacity values having less accuracy than either low or high range
opacity values.
Esterline Angus. Of 3 Esterline Angus monitors audited, one unit had
problems with monitor alignment and panel meter errors. Optical dust
accumulations were found to be minimal, thereby indicating adequate monitor
maintenance. Furthermore, only one unit was found to have excessive
calibration error (high range). Monitor accuracy and linearity, as
illustrated in Figure 5, were satisfactory, with both low and mid-range
calibration errors falling well within the +3 percent error band.
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IV. CONCLUSIONS AND RECOMMENDATIONS
General Conclusions
1. Opacity monitoring systems installed at stationary sources
typically achieve high levels of availability (approximately 95
percent)
2. Contemporary opacity monitoring instrumentation is capable of
providing accurate emissions monitoring data.
3- Problems impacting opacity monitoring data quality are generally
limited to monitor miscalibration and/or adjustment, as well as
improper or inadequate operation and maintenance practices.
4. The opacity monitor performance audit procedures which have been
evaluated provide a reliable indication of the accuracy of opacity
monitoring data and the adequacy of monitor operation and
maintenance practices.
Specific Conclusions
1. Monitors which were properly operated and maintained demonstrated
acceptable performance relative to audit test criteria and
provided accurate opacity monitoring data.
2. Most installed opacity monitors are not affected by optical
alignment problems. However, opacity monitoring systems provided
by one manufacturer may be more susceptible to alignment problems
than other monitoring systems.
3. Incorrect stack exit correction factors for opacity monitoring
systems are often encountered.
4. Inappropriate methods are frequently used for determining
stack-exit opacity where multiple opacity monitors are installed
in separate ducts which are exhausted through a common stack.
5. Measurement values displayed on monitor panel meters are often
inaccurate and are generally less reliable than strip chart
readings.
6. Monitor responses to internal zero and span checks are in excess
of acceptable limits in many cases; however, a direct correlation
between zero and span check results and calibration error test
results has not been observed.
7. Automatic zero compensation circuits generally provide a reliable
indication of dust accumulation on the transceiver optics;
however, some monitor operators are not aware of the 4 percent
opacity zero compensation limit and/or incorrectly interpret the
zero compensation value.
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Dust accumulation on exposed optical surfaces is both site- and
monitor-specific and may occur at different rates for the
transceiver and reflector components. Excess dust accumulation on
optical surfaces was observed for approximately 19 percent of the
audited monitors.
Calibration error test results in excess of the acceptable limits
occurred most frequently at high opacity levels; the magnitude of
calibration errors was found to increase as the measured opacity
increased. Poorly performing monitors tended to provide
measurements which were biased high relative to the correct value.
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Recommendations
The following recommendations are offered for those source operators
where installed opacity monitoring systems failed to demonstrate acceptable
performance during audits.
1. The personnel who perform the required daily zero and span checks
should receive adequate training to allow them to perform routine
adjustments, as necessary, to eliminate excessive zero drift, span
drift, and discrepancies between the control panel display values
and the permanent data recording system. This training should be
monitor-specific and should include adequate explanation, as
applicable, of automatic zero compensation functions, stack exit
correction factors, and procedures for determining equivalent
calibration filter values corrected for stack exit conditions.
2. After all calibration/adjustment problems observed during audits
are corrected , monitor operators should institute a well defined
operation and maintenance program for the opacity monitoring
systems. Such a program must address monitor-specific and
site-specific considerations, and should at least include the
following activities:
a. daily checks, and as necessary, adjustment of: fault lamp
indications, zero drift, span drift, panel meter accuracy,
data recorder adjustment, and available monitor-specific
operational indicators,
b. periodic evaluation and, as necessary, corrective actions for
dust accumulation on exposed optical surfaces, optical
alignment, reference voltages/curf ents, etc.
c. routine maintenance as specified by the manufacturer and
including: replacement of measurement lamps, fault lamp
bulbs, purge air filters, dessicant, etc.
The appropriate frequency for performing periodic evaluations and
routine maintenance should be established through a trial and
error procedure. Such a procedure involves: (1) selecting an
initial frequency for these activities, (2) performing periodic
evaluations and routine maintenance and documenting results of
these activities over a sufficient period of time to evaluate
their impact on monitor performance, and (3) modifying the
initially selected frequency in view of the results obtained in
order to minimize the expenditure of resources while consistently
monitoring instrument performance within acceptable limits.
3. Monitor operators should institute a self auditing program which
includes a calibration error determination at three points over
the measurement range of the instrument. At a minimun, this
procedure should be performed concurrently with the required
annual optical and zero alignments of Performance Specification 1,
Appendix B, 40 CFR 60. The frequency of self-audits should be
adjusted as necessary, to maintain instrument performance within
acceptable limits.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO. 2 '"
EPA- 340/1-83 /Oil
4. TITLE AND SUBTITLE
A Compilation of Opacity Monitor Performance Audit
Results
7. AUTHOR(S)
Steve Plaisance
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Entropy Environmentalists, Inc.
P.O. Box 12291
Research Triangle Park, NC 27709
12. SPONSORING AGENCY NAME AND ADDRESS
OAQPS
Stationary Source Compliance Division
Waterside Mall, 401 M Street, SW
Washington, DC 20460
3. RECIPIENT'S ACCESSION NO.'
5. REPORT DATE
January 1983
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT N
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-01-6317
13. TYPE OF REPORT AND PERIOD COVERE
FINAL - IN-HOUSE
14. SPONSORING AGENCY CODE
EPA/200/04
15. SUPPLEMENTARY NOTES
Opacity monitor performance audit procedures and devices have been developed and
field tested on 93 opacity monitors. The results of this test program indicate that
opacity monitoring systems achieve high levels of availability, and are capable of
providing accurate emissions data. The results also show that problems impacting
data quality are generally limited to monitor miscalibration and/or misadjustment,
as well as improper or inadequate operating and maintenance practices. It is be-
lieved that improved monitor performance and data reliability can be achieved with
additional training of monitor operators and more frequent performance audits.
This document describes the audit program for continuous emission monitors (CEMs)
of effluent opacity. Detailed explanations of the audit methodology, monitor ana-
lyses, and analytical criteria are included, and both criteria- and monitor-specific
results of installed opacity monitor audits are delineated. Finally, conclusions
are drawn as to the adequacy of monitor performance and data reliability, and recom-
mendations are offered that can optimize opacity monitoring system performance.-
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
Air Pollution
Opacity Monitoring Systems
18. DISTRIBUTION STATEMENT
Release to Public
b. IDENTIFIERS/OPEN ENDED TERMS
Audit Results
19. SECURITY CLASS (This Report)
unclassified
20. SECURITY CLASS (This page)
unclassified
c. COSATI Field/Group
21. NO. OF PAGES
42
22. PRICE
EPA Form 2220-1 (R«v. 4-77) PREVIOUS EDITION is OBSOLETE
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Environmental Protection Stationary Source Compliance Division
Agency Washington, D C 20460
Official Business Publication No EPA-340/1-83-011 Postage and
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