2.1.2.6 Response Time. The time interval between the start of a step change in the system input (e.g., change of calibration gas) and the time when the data recorder displays 95% of the final value.
2.1.2.7 Accuracy. A measure of agreement between a measured value and an accepted or true value, expressed as the percentage difference between the true and measured values relative to the true value. For these performance specifications, accuracy is checked by conducting a calibration error (CE) test and a relative accuracy (RA) test. Certain facilities, such as those using solid waste or batch-fed processes, may observe long periods of almost no CO emissions with brief, high-level CO emission spikes. These facilities, as well as facilities whose CO emissions never exceed 5-10 ppm, may need to be exempted from the RA requirement because the RA test procedure cannot ensure acquisition of meaningful test results under these conditions. An alternative procedure for accuracy determination is described in section 2.1.9.
2.1.2.8 Calibration Error (CE). The difference between the concentration indicated by the CEMS and the known concentration of the cylinder gas. A CE test procedure is performed to document the accuracy and linearity of the monitoring equipment over the entire measurement range.
2.1.2.9 Relative Accuracy (RA). A comparison of the CEMS response to a value measured by a performance test method (PTM). The PA test is used to validate the calibration technique and verify the ability of the CEMS to provide representative and accurate measurements.
2.1.2.10 Performance Test Method (PTM). The sampling and analysis procedure used to obtain reference measurements for comparison to CEMS measurements. The applicable test methods are Method 10, 10A, or 10B (for the determination of CO) and Method 3 or 3A (for the determination of 0
2). These methods are found in
40 CFR part 60, Appendix A, incorporated by reference in s.
NR 660.11.
2.1.2.11 Performance Specification Test (PST) Period. The period during which CD, CE, response time, and RA tests are conducted.
2.1.2.12 Centroidal Area. A concentric area that is geometrically similar to the stack or duct cross section and is no greater than one percent of the stack or duct cross-sectional area.
2.1.3 Installation and Measurement Location
Specifications
2.1.3.1 CEMS Installation and Measurement Locations. The CEMS shall be installed in a location in which measurements representative of the source's emissions can be obtained. The optimum location of the sample interface for the CEMS is determined by a number of factors, including ease of access for calibration and maintenance, the degree to which sample conditioning will be required, the degree to which it represents total emissions, and the degree to which it represents the combustion situation in the firebox. The location should be as free from in-leakage influences as possible and reasonably free from severe flow disturbances. The sample location should be at least 2 equivalent duct diameters downstream from the nearest control device, point of pollutant generation, or other point at which a change in the pollutant concentration or emission rate occurs and at least 0.5 diameter upstream from the exhaust or control device. The equivalent duct diameter is calculated as per section 2.1 of
40 CFR part 60, Appendix A, method 1, incorporated by reference in s.
NR 660.11. If these criteria are not achievable or if the location is otherwise less than optimum, the possibility of stratification should be checked as described in Section 2.1.3.3 to determine whether the location would cause failure of the relative accuracy test.
2.1.3.1.1 For extractive or point in-situ CEMSs, the measurement point should be within or centrally located over the centroidal area of the stack or duct cross section.
2.1.3.1.2 For cross-stack CEMSs, the effective measurement path should (1) have at least 70% of the path within the inner 50% of the stack or duct cross-sectional area or (2) be centrally located over any part of the centroidal area.
2.1.3.1.3 Both the CO and O2 monitors should be installed at the same general location. If this is not possible, they may be installed at different locations if the effluent gases at both sample locations are not stratified and there is no in-leakage of air between sampling locations.
2.1.3.2 Performance Test Method (PTM) Measurement Location and Traverse Points.
2.1.3.2.1 Select an accessible PTM measurement point at least 2 equivalent diameters downstream from the nearest control device, the point of CO generation, or other point at which a change in the CO concentration may occur, and at least 1/2 equivalent diameter upstream from the effluent exhaust or control device. When pollutant concentration changes are due solely to diluent leakage (e.g., air heater leakages) and CO and O2 are simultaneously measured at the same location, 1/2 diameter may be used in place of 2 equivalent diameters. The CEMS and PTM locations need not be the same.
2.1.3.2.2 Select traverse points that ensure acquisition of representative samples over the stack or duct cross section. At a minimum, establish a measurement line that passes through the centroidal area in the direction of any expected stratification. If this line interferes with the CEMS measurements, displace the line up to 30 cm (or 5% of the equivalent diameter of the cross section, whichever is less) from the centroidal area. Locate 3 traverse points at 17, 50, and 83% of the measurement line. If the measurement line is no longer than 2.4 meters and pollutant stratification is not expected, the tester may choose to locate the 3 traverse points on the line at 0.4, 1.2, and 2.0 meters from the stack or duct wall. This option may not be used at a site located within 8 equivalent diameters downstream of a flow disturbance. The tester may select other traverse points, if they can be shown to the satisfaction of the department to provide a representative sample over the stack or duct cross-section. Conduct all necessary PTM tests within 3 cm of the selected traverse points. Sampling may not be performed within 3 cm of the duct or stack inner wall.
2.1.3.3 Stratification Test Procedure. Stratification is defined as a difference in excess of 10% between the average concentration in the duct or stack and the concentration at any point more than 1.0 meter from the duct or stack wall. To determine whether effluent stratification exists, a dual probe system should be used to determine the average effluent concentration while measurements at each traverse point are being made. One probe, located at the stack or duct centroid, is used as a stationary reference point to indicate the change in effluent concentration over time. The second probe is used for sampling at the traverse points specified in
40 CFR part 60, Appendix A, method 1, incorporated by reference in s.
NR 660.11. The monitoring system samples sequentially at the reference and traverse points throughout the testing period for 5 minutes at each point.
2.1.4 CEMS Performance and Equipment Specifications
Table 2.1-1 summarizes the performance specifications for the CEMSs. Two sets of standards for CO are given; one for low-range and another for high-range measurements. The high-range specifications relate to measurement and quantification of short duration high concentration peaks, while the low-range specifications relate to the overall average operating condition of the burning device. The dual-range specifications can be met by using (1) one analyzer for each range, (2) a dual range unit, or (3) a single measurement range instrument capable of meeting both specifications with a single unit. Adjustments cannot be made to the analyzer between determinations of low- and high-level accuracy within the single measurement range. In the second case, when the concentration exceeds the span of the lower range, the data acquisition system recorder shall switch to the high range automatically.
2.1.4.1 CEMS Span Value. In order to measure high and low concentrations with the same or similar degree of accuracy, the maximum ranges (span values) are specified for low and high range analyzers. The span values are listed in Table 2.1-2. Tier I and Tier II format definitions are established in subch. H.
Table 2.1-1
1For Tier II, CD and CE are 3% and 5% of twice the license limit, respectively.
2Expressed as the sum of the mean absolute value plus the 95% confidence interval of a series of measurements.
2.1.4.2 Daily Calibration Gas Values. The owner or operator shall choose calibration gas concentrations (or calibration filters for in-situ systems) that include zero and high-level calibration values for the daily calibration checks. For a single measurement range monitor, 3 CO calibration gas concentrations (or calibration filters for in-situ systems) shall be used, i.e., the zero and high-level concentrations of the low-range CO analyzer and the high-level concentration of the high-range CO analyzer.
2.1.4.2.1 The zero level for the CO or O2 analyzer may be between 0 and 20% of the span value, e.g., 0-40 ppm for low-range CO analyzer, 0-600 ppm for the high-range CO analyzer, and 0-5% for the O2 analyzer (for Tier I).
2.1.4.2.2 The high-level concentration for the CO or O2 analyzer shall be between 50 and 90% of the span value, i.e., 100-180 ppm for the low-range CO analyzer, 1500-2700 ppm for the high-range CO analyzer, and 12.5-22.5% O2 for the O2 analyzer.
2.1.4.3 Data Recorder Scale. The strip chart recorder, computer, or digital recorder shall be capable of recording all readings within the CEMS's measurement range and shall have a resolution of 0.5% of span value, i.e., one ppm CO for low-range CO analyzer, 15 ppm CO for high-range CO analyzer, and 0.1% O2 for the O2 analyzer.
2.1.4.4 Response Time. The response time for the CO or O2 monitor may not exceed 2 minutes to achieve 95% of the final stable value.
2.1.4.5 Calibration Drift. The CEMS shall allow the determination of CD at the zero and high-level values. The CD shall be determined separately for CO and O2 monitors in terms of concentration. The CO CEMS calibration response may not drift or deviate from the reference value of the calibration gas (or calibration filters for in-situ systems) by more than 3% of the span value after each 24-hour period of the 7-day test, i.e., 6 ppm CO for the low-range analyzer (Tier I) and 90 ppm for the high-range analyzer, at both zero and high levels. The O2 monitor calibration response may not drift or deviate from the reference value by more than 0.5% O2 at both zero and high levels.
2.l.4.6 Relative Accuracy. The result of the PA test of the CO CEMS (which incorporates the O2 monitor) shall be no greater than 10% of the mean value of the PTM results or shall be within 10 ppm CO of the PTM results, whichever is less restrictive. The ppm CO concentration shall be corrected to 7% O2 before calculating the RA.
2.1.4.7 Calibration Error. The mean difference between the CEMS and reference values at all 3 test points (see Table 2.1-3) shall be no greater than 5% of span value for CO monitors (i.e., 10 ppm CO for low range Tier I CO analyzers and 150 ppm CO for high range CO analyzers) and 0.5% for O2 analyzers.
2.1.4.8 Measurement and Recording Frequency. The sample to be analyzed shall pass through the measurement section of the analyzer without interruption. The detector shall measure the sample concentration at least once every 15 seconds. An average emission rate shall be computed and recorded at least once every 60 seconds.
2.1.4.9 Hourly Rolling Average Calculation. The CEMS shall calculate every minute an hourly rolling average, which is the arithmetic mean of the 60 most recent one-minute average values.
2.1.4.10 Retest. If the CEMS produces results within the specified criteria, the test is successful. If the CEMS does not meet one or more of the criteria, the necessary corrections shall be made and the performance tests repeated.
2.1.5 Test Periods
2.1.5.1 Pretest Preparation Period. Install the CEMS, prepare the PTM test site according to the specifications in section 2.1.3, and prepare the CEMS for operation and calibration according to the manufacturer's written instructions. A pretest conditioning period similar to that of the 7-day CD test is recommended to verify the operational status of the CEMS.
2.1.5.2 Calibration Drift Test Period. While the facility is operating under normal conditions, determine the CD at 24-hour intervals for 7 consecutive days according to the procedure given in section 2.1.6.1. All CD determinations shall be made following a 24-hour period during which no unscheduled maintenance, repair, or adjustment takes place. If the combustion unit is taken out of service during the test period, record the onset and duration of the downtime and continue the calibration drift test when the unit resumes operation.
2.1.5.3 Relative Accuracy Test Period. Conduct the RA test according to the procedure in section 2.1.6.4 while the facility is operating under normal conditions. RA testing for CO and O2 shall be conducted simultaneously so that the results can be calculated for CO corrected to 7% O2. The RA test shall be conducted during the CD test period. It is emphasized that during the CD test period, no adjustments or repairs may be made to the CEMS other than routine calibration adjustments performed immediately following the daily CD determination.
2.1.5.4 Calibration Error Test and Response Time Test Periods. Conduct the CE and response time tests during the CD test period.
2.1.6 Performance Specification Test Procedures
2.1.6.1 Calibration Drift Test.
2.1.6.1.1 Sampling Strategy. Conduct the CD test for all monitors at 24-hour intervals for 7 consecutive days using calibration gases at the 2 (or 3, if applicable) concentration levels specified in section 2.1.4.2. Introduce the calibration gases into the sampling system as close to the sampling probe outlet as practical. The gas shall pass through all filters, scrubbers, conditioners, and other CEMS components used during normal sampling. If periodic automatic or manual adjustments are made to the CEMS zero and calibration settings, conduct the CD test immediately before these adjustments, or conduct it in such a way that the CD can be determined. Record the CEMS response and subtract this value from the reference (calibration gas) value. To meet the specification, none of the differences shall exceed the limits specified in Table 2.1-1.
2.1.6.1.2 Calculations. Summarize the results on a data sheet. An example is shown in Figure 2.1-1. Calculate the differences between the CEMS responses and the reference values.
2.1.6.2 Response Time. Check the entire CEMS including sample extraction and transport, sample conditioning, gas analyses, and the data recording.
2.1.6.2.1 Introduce zero gas into the system. For extractive systems, introduce the calibration gases at the probe as near to the sample location as possible. For in-situ system, introduce the zero gas at a point such that all components active in the analysis are tested. When the system output has stabilized (no change greater than one percent of full scale for 30 seconds), switch to monitor stack effluent and wait for a stable value. Record the time (upscale response time) required to reach 95% of the final stable value.
2.1.6.2.2 Next, introduce a high-level calibration gas and repeat the above procedure. Repeat the entire procedure 3 times and determine the mean upscale and downscale response times. The longer of the 2 means is the system response time.
2.1.6.3 Calibration Error Test Procedure.
2.1.6.3.1 Sampling Strategy. Challenge each monitor (both low- and high-range CO and O2) with zero gas and EPA Protocol 1, incorporated by reference in s.
NR 660.11, cylinder gases at 3 measurement points within the ranges specified in Table 2.1-3.
-
See PDF for table 
1For Tier II, the CE specifications for the low-range CO CEMS are 0-20%, 30-40%, and 70-80% of twice the license limit.
2.1.6.3.1.1 If a single measurement range is used, the calibration gases used in the daily CD checks (if they are Protocol 1 cylinder gases and meet the criteria in section 2.1.6.3.1) may be used for determining CE.
2.1.6.3.1.2 Operate each monitor in its normal sampling mode as nearly as possible. The calibration gas shall be injected into the sample system as close to the sampling probe outlet as practical and should pass through all CEMS components used during normal sampling. Challenge the CEMS 3 non-consecutive times at each measurement point and record the responses. The duration of each gas injection should be sufficient to ensure that the CEMS surfaces are conditioned.
2.1.6.3.2 Calculations. Summarize the results on a data sheet. An example data sheet is shown in Figure 2.1-2. Average the differences between the instrument response and the certified cylinder gas value for each gas. Calculate 3 CE results (5 CE results for a single-range CO CEMS) according to Equation 5 (section 2.1.7.5). No confidence coefficient is used in CE calculations.
2.1.6.4 Relative Accuracy Test Procedure.
2.1.6.4.1 Sampling Strategy for PTM tests. Conduct the PTM tests in such a way that they will yield measurements representative of the emissions from the source and can be correlated to the CEMS data. Although it is preferable to conduct the CO, diluent, and moisture (if needed) simultaneously, moisture measurements that are taken within a 60-minute period which includes the simultaneous CO and O2 measurements may be used to calculate the dry CO concentration.
Note: At times, CEMS RA tests may be conducted during incinerator performance tests. In these cases, PTM results obtained during CEMS RA tests may be used to determine compliance with incinerator emissions limits as long as the source and test conditions are consistent with the applicable regulations.
2.1.6.4.2 Performance Test Methods.
2.1.6.4.2.1 Unless otherwise specified in the regulations, method 3 or 3A and method 10, 10A, or 10B (
40 CFR part 60, Appendix A, incorporated by reference in s.
NR 660.11) are the test methods for O
2 and CO, respectively. Make a sample traverse of at least 21 minutes, sampling for 7 minutes at each of 3 traverse points (see section 3.2).
2.1.6.4.2.2 When the installed CEMS uses a nondispersive infrared (NDIR) analyzer, method 10 shall use the alternative interference trap specified in section 10.1 of the method. An option, which may be approved by the department in certain cases, would allow the test to be conducted using method 10 without the interference trap. Under this option, a laboratory interference test is performed for the analyzer prior to the field test. The laboratory interference test includes the analysis of SO, NO, and CO calibration gases over the range of expected effluent concentrations. Acceptable performance is indicated if the CO analyzer response to each of the gases is less than one percent of the applicable measurement range of the analyzer.
2.1.6.4.3 Number of PTM Tests. Conduct a minimum of 9 sets of all necessary PTM tests. If more than 9 sets are conducted, a maximum of 3 sets may be rejected at the tester's discretion. The total number of sets used to determine the RA shall be greater than or equal to 9. All data, including the rejected data, shall be reported.
2.1.6.4.4 Correlation of PTM and CEMS Data. The time and duration of each PTM test run and the CEMS response time should be considered in correlating the data. Use the CEMS final output (the one used for reporting) to determine an integrated average CO concentration for each PTM test run. Confirm that the pair of results are on a consistent moisture and O2 concentration basis. Each integrated CEMS value should then be compared against the corresponding average PTM value. If the CO concentration measured by the CEMS is normalized to a specified diluent concentration, the PTM results shall be normalized to the same value.
2.1.6.4.5 Calculations. Summarize the results on a data sheet. Calculate the mean of the PTM values and calculate the arithmetic differences between the PTM and the CEMS data sets. The mean of the differences, standard deviation, confidence coefficient, and CEMS RA should be calculated using Equations one through 4.
2.1.7 Equations
where:
n = Number of data points.
When the mean of the differences of pairs of data is calculated, correct the data for moisture, if applicable.
2.1.7.2 Standard Deviation (Sd). Calculate S
d using Equation 2.
2.1.7.3 Confidence Coefficient (CC). Calculate the 2.5% error CC (one-tailed) using Equation 3.
where:
a The values in this table are already corrected for n-1 degrees of freedom. Use n equal to the number of individual values.
2.1.7.4 Relative Accuracy. Calculate the RA of a set of data using Equation 4.
where:
2.1.7.5 Calibration Error. Calculate CE using Equation 5.
where:
