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applies only to orifice meters having a constant orifice coefficient. The coefficient for the calibrating orifice described in 5.1.4 bas been shown experimentally to be constant over the normal operating range of the highvolume sampler (0.6 to 2.2 m.3/min.; 20 to 78 ft.3/min.). Calculate corrected flow rate:

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Q=Average sampling rate, m.3/min.

T=Sampling time, minutes. The average sampling rate, Q, is determined from the recorder chart by estimation if the flow rate does not vary more than 0.11 m.37 min. (4 ft.3/min.) during the sampling period. If the flow rate does vary more than 0.11 m.8 (4 ft.3/min.) during the sampling period, read the flow rate from the chart at 2-hour intervals and take the average.

B. Pressure and Temperature Corrections.

If the pressure or temperature during high-volume sampler calibration is substantially different from the pressure or temperature during orifice calibration, a correction of the flow rate, Q, may be required. If the pressures differ by no more than 15 percent and the temperatures differ by no more than 100 percent (°C), the error in the uncorrected flow rate will be no more than 15 percent. If necessary, obtain the corrected flow rate as directed below. This correction

LT P2 Qa=Corrected flow rate, m.3/min. Qı=Flow rate during high-volume sampler

calibration (Section 8.1.2), m.3/min. Ty=Absolute temperature during orifice

unit calibration (Section 8.1.1), *K

or 'R. Pi=Barometric pressure during orifice unit

calibration (Section 8.1.1), mm. Hg. Ty=Absolute temperature during high

volume sampler calibration (Section

8.1.2), 'K or 'R. Po=Barometric pressure during high-vol

ume sampler calibration (Section 8.1.2), mm. Hg.

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APPENDIX C-REFERENCE METHOD FOR THE changes in instrument response. Zero drift

CONTINUOUS MEASUREMENT OF CARBON is usually less than +1 percent of full scale MONOXIDE IN THE ATMOSPHERE (NON per 24 hours, if cell temperature and presDISPERSIVE INFRARED SPECTROMETRY

sure are maintained constant. 1. Principle and Applicability.

5. Apparatus. 1.1 This method is based on the absorp

5.1 Carbon Monoxide Analyzer. Commertion of infrared radiation by carbon mon

cially available instruments should be inoxide, Energy from a source emitting radia

stalled on location and demonstrated, preftion in the infrared region is directed

erably by the manufacturer, to meet or through reference and sample cells. Both

exceed manufacturers specifications and beams pass into matched cells, each contain

those described in this method. ing a selective detector and CO. The co in

5.2 Sample Introduction System. Pump,

flow control valve, and flowmeter. the cells absorb infrared radiation only at its

5.3 Filter (In-line). A filter with a poroscharacteristic frequencies and the detector is

ity of 2 to 10 microns should be used to sensitive to those frequencies. With a nonabsorbing gas in the reference cell, and with

keep large particles from the sample cell. no co in the sample cell, the signals from

5.4 Moisture Control. Refrigeration units both detectors are balanced electronically.

are available with some commercial instru

ments for maintaining constant humidity. Any Co introduced into the sample cell will

Drying tubes (with sufficient capacity to opabsorb radiation, which reduces the temper

erate for 72 hours) containing indicating ature and pressure in the detector cell and

silica gel can be used. Other techniques that displaces a diaphram. This displacement is

prevent the interference of moisture are detected electronically and amplified to pro

satisfactory. vide an output signal.

6. Reagents. 1.2 This method is applicable to the determination of carbon monoxide in ambient

6.1 Zero Gas. Nitrogen or helium contain

ing less than 0.1 mg. CO/m.3 air, and to the analysis of gases under

6.2 Calibration Gases. Calibration gases pressure.

corresponding to 10, 20, 40, and 80 percent 2. Range and Sensitivity.

of full scale are used. Gases must be pro2.1 Instruments are available that meas

vided with certification or guaranteed analure in the range of 0 to 58 mg./m.3 (0-50

ysis of carbon monoxide content. p.p.m.), which is the range most commonly

6.3 Span Gas. The calibration gas correused for urban atmospheric sampling. Most instruments measure in additional ranges.

sponding to 80 percent of full scale is used

to span the instrument. 2.2 Sensitivity is 1 percent of full-scale

7. Procedure. response per 0.6 mg. CO/m.8 (0.5 p.p.m.).

7.1 Calibrate the instrument as described 3. Interferences. 3.1 Interferences vary between individual

in 8.1. All gases (sample, zero, calibration,

and span) must be introduced into the eninstruments. The effect of carbon dioxide

tire analyzer system. Figure Ci shows a interference at normal concentrations is

typical flow diagram. For specific operating minimal. The primary interference is water vapor, and with no correction may give an

instructions, refer to the manufacturer's

manual. interference equivalent to as high as 12 mg.

8. Calibration. CO/m.3 Water vapor interference can be

8.1 Calibration Curve. Determine the minimized by (a) passing the air sample

linearity of the detector response at the through silica gel or similar drying agents,

operating flow rate and temperature. Pre(b) maintaining constant humidity in the

pare a calibration curve and check the curve sample and calibration gases by refrigeration, (c) saturating the air sample and cali

furnished with the instrument. Introduce bration gases to maintain constant humid

zero gas and set the zero control to indicate ity or (d) using narrowband optical filters

a recorder reading of zero. Introduce span in combination with some of these measures. gas and adjust the span control to indicate

3.2 Hydrocarbons at ambient levels do the proper value on the recorder scale (e.g. not ordinarily interfere.

on 0-58 mg./m.8 scale, set the 46 mg./m.3 4. Precision, Accuracy, and Stability. standard at 80 percent of the recorder 4.1 Precision determined with calibration

chart). Recheck zero and span until adjustgases is +0.5 percent full scale in the 0-58

ments are no longer necessary. Introduce mg./m.3 range. 4.2 Accuracy depends on instrument

intermediate calibration gases and plot the

values obtained. If a smooth curve is not linearity and the absolute concentrations of the calibration gases. An accuracy of +1

obtained, calibration gases may need percent of full scale in the 0-58 mg./m.8


9. Calculations. range can be obtained.

9.1 Determine the concentrations directly 4.3 Variations in ambient room temperature can cause changes equivalent to as

from the calibration curve. No calculations much as 0.5 mg. CO/m.3 per °C. This effect

are necessary. can be minimized by operating the analyzer

9.2 Carbon monoxide concentrations in in & temperature-controlled room. Pressure

mg./m.3 are converted to p.p.m, as follows: changes between span checks will cause

p.p.m. CO=mg. CO/m.3 x 0.873


10. Bibliography.

The Intech NDIR-CO Analyzer by Frank McElroy. Presented at the 11th Methods Conference in Air Pollution, University of California, Berkeley, Calif., April 1, 1970.

Jacobs, M. B. et al., J.A.P.C.A. 9, No. 2, 110-114, August 1959.

MSA LIRA Infrared Gas and Liquid Analyzer Instruction Book, Mine Safety Appliances Co., Pittsburgh, Pa.

Beckman Instruction 1635B, Models 215A, 315A and 415A Infrared Analyzers, Beckman Instrument Company, Fullerton, Calif.

Continuous CO Monitoring System, Model A 5611, Intertech Corp., Princeton, N.J.

Bendix-UNOR Infrared Gas Analyzers. Ronceverte, W. Va.


A. Suggested Performance Specifications for NDIR Carbon Monoxide Analyzers: Range (minimum)------ 0-58 mg./m.3

(0-50 p.p.m.). Output (minimum)----- 0-10, 100, 1,000,

5,000 mv. full

scale. Minimum detectable sen- 0.6 mg./m.3 (0.5 sitivity.

p.p.m.). Lag time (maximum)--15 seconds. Time to 90 percent re- 30 seconds.

sponse (maximum). Rise time, 90 percent 15 seconds.

(maximum). Fall time, 90 percent 15 seconds.

(maximum). Zero drift (maximum)--- 3 percent / week,

not to exceed 1 percent/24

hours. Span drift (maximum)-- 3 percent/week,

not to exceed 1 percent/24

hours. Precision (minimum)--- +0.5 percent. Operational period (min. 3 days.

imum). Noise (maximum)------- +0.5 percent. Interference equivalent 1 percent of full (maximum).

scale. Operating temperature 5–40° C.

range (minimum). Operating humidity range 10–100 percent.

(minimum). Linearity (maximum de- 1 percent of full viation).

scale. B. Suggested Definitions of Performance Specifications: Range-The minimum and maximum meas

urement limits. Output-Electrical signal which is propor

tional to the measurement; intended for connection to readout or data processing devices. Usually expressed as millivolts or milliamps full scale at a given impedance.

Full Scale—The maximum measuring limit

for a given range. Minimum Detectable Sensitivity—The small

est amount of input concentration that can be detected as the concentration ap

proaches zero. Accuracy-The degree of agreement between

a measured value and the true value; usu

ally expressed as + percent of full scale. Lag Time-The time interval from a step

change in input concentration at the instrument inlet to the first corresponding

change in the instrument output. Time to 90 Percent Response—The time in

terval from a step change in the input concentration at the instrument inlet to a reading of 90 percent of the ultimate

recorded concentration. Rise Time (90 percent)-The interval be

tween initial response time and time to 90 percent response after a step increase in

the inlet concentration. Fall Time (90 percent)-The interval be

tween initial response time and time to 90 percent response after a step decrease

in the inlet concentration. Zero Drift—The change in instrument out

put over a stated time period, usually 24 hours, of unadjusted continuous operation, when the input concentration is zero; usually expressed as percent full

scale. Span Drift—The change in instrument output over a stated time period, usually 24 hours, of unadjusted continuous operation, when the input concentration is a stated upscale value; usually expressed as

percent full scale. Precision-The degree of agreement between

repeated measurements of the same concentration, expressed as the average devia

tion of the single results from the mean. Operational Period—The period of time over

which the instrument can be expected to

operate unattended within specifications. Noise-Spontaneous deviations from a mean

output not caused by input concentration

changes. Interference-An undesired positive or nega

tive output caused by a substance other

than the one being measured. Interference Equivalent-The portion of

indicated input concentration due to the

presence of an interferent. Operating Temperature Range-The range of ambient temperatures over which the instrument will meet all performance specifications. Operating Humidity Range The range of

ambient relative humidity over which the instrument will meet all performance

specifications. Linearity—The maximum deviation between

an actual instrument reading and the reading predicted by a straight line drawn between upper and lower calibration points.

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1. Principle and Applicability.

1.1 Ambient air and ethylene are delivered simultaneously to a mixing zone where the ozone in the air reacts with the ethylene to emit light which is detected by a photomultiplier tube. The resulting photocurrent is amplified and is either read directly or displayed on a recorder.

1.2 The method is applicable to the continuous measurement of ozone in ambient air.

2. Range and Sensitivity.

2.1 The range is 9.8 ug. 02/m.s to greater than 1960 ug. 03/m.8 (0.005 p.p.m. Og to greater than 1 p.p.m. Oz).

2.2 The sensitivity is 9.8 ug. 03/m.8 (0.005 p.p.m. O3).

3. Interferences.

3.1 Other oxidizing and reducing species normally found in ambient air do not interfere.

4. Precision and Accuracy.

4.1 The average deviation from the mean of repeated single measurements does not exceed 5 percent of the mean of the measurements.

4.2 The method is accurate within +7 percent.

5. Apparatus.

5.1 Detector Cell. Figure D1 is a drawing of a typical detector cell showing flow paths

of gases, the mixing zone, and placement of the photomultiplier tube. Other flow paths in which the air and ethylene streams meet at a point near the photomultiplier tube are also allowable.

5.2 Air Flowmeter. A device capable of controlling air flows between 0-1.5 1/min,

5.3 Ethylene Flowmeter. A device capable of controlling ethylene flows between 0-50 ml./min. At any flow in this range, the device should be capable of maintaining constant flow rate within +3 ml./min.

5.4 Air Inlet Filter. A Teflon filter capable of removing all particles greater than 5 microns in diameter.

5.5 Photomultiplier Tube. A high gain low dark current (not more than 1x10-9 ampere) photomultiplier tube having its maximum gain at about 430 nm. The following tubes are satisfactory: RCA 4507, RCA 8575, EMI 9750, EMI 9524, and EMI 9536.

5.6 High Voltage Power Supply. Capable of delivering up to 2,000 volts of regulated power.

5.7 Direct Current Amplifier. Capable of full scale ampliucation of currents from 10-10 to 10-7 ampere; an electrometer is commonly used.

5.8 Recorder. Capable of full scale display of voltages from the DC amplifier. These voltages commonly are in the 1 millivolt to 1-volt range.

5.9 Ozone Source and Dilution System. The ozone source consists of a quartz tube

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