IEST RP-CC014 2-2010 Calibration and Characterization of Optical Airborne Particle Counters.pdf

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1、 Institute of Environmental Sciences and Technology IEST-RP-CC014.2 Contamination Control Division Recommended Practice 014.2 Calibration and Characterization of Optical Airborne Particle Counters Arlington Place One 2340 S. Arlington Heights Road, Suite 100 Arlington Heights, IL 60005-4516 Phone: (

2、847) 981-0100 Fax: (847) 981-4130 E-mail: informationiest.org Web: www.iest.org 2 IEST 2010 All rights reserved Institute of Environmental Sciences and Technology IEST-RP-CC014.2 This Recommended Practice is published by the Institute of Environmental Sciences and Technology to advance the technical

3、 and engineering sciences. Use of this document is entirely voluntary, and determination of its applicability and suitability for any particular use is solely the responsibility of the user. Use of this Recommended Practice does not imply any warranty or endorsement by IEST. This Recommended Practic

4、e was prepared by and is under the jurisdiction of Working Group 014 of the IEST Con-tamination Control Division. Copyright 2010 by the Institute of Environmental Sciences and Technology First printing, August 2010 ISBN 978-0-9841330-3-1 PROPOSAL FOR IMPROVEMENT: The Working Groups of the Institute

5、of Environmental Sciences and Technology are continually working on improvements to their Recommended Practices and Reference Docu-ments. Suggestions from users of these documents are welcome. If you have a suggestion regarding this docu-ment, please use the online Proposal for Improvement form foun

6、d on the IEST website at www.iest.org. Institute of Environmental Sciences and Technology Arlington Place One 2340 S. Arlington Heights Road, Suite 100 Arlington Heights, IL 60005-4516 Phone: (847) 981-0100 Fax: (847) 981-4130 E-mail: informationiest.org Web: www.iest.org IEST-RP-CC014.2 Institute o

7、f Environmental Sciences and Technology IEST 2010 All rights reserved 3 Calibration and Characterization of Optical Airborne Particle Counters IEST-RP-CC014.2 CONTENTS SECTION 1 SCOPE AND LIMITATIONS . 5 2 REFERENCES 5 3 TERMS AND DEFINITIONS . 6 4 BACKGROUND AND PURPOSE . 7 5 REQUIREMENTS 7 6 CALIB

8、RATION OF INLET FLOW RATE . 8 7 PARTICLE SIZE CALIBRATION . 9 8 FALSE COUNT 11 9 COUNTING EFFICIENCY METHOD 1 . 12 10 COUNTING EFFICIENCY METHOD 2 . 15 11 RESPONSE RATE 16 12 CONCENTRATION (COINCIDENCE) LIMIT . 17 13 RESOLUTION 18 FIGURE FIGURE 1NON-MONOTONIC REGION OF AN OPC CALIBRATION CURVE. . 9

9、FIGURE 2DETERMINATION OF MEDIAN VOLTAGE USING A PHA DISTRIBUTION. . 10 FIGURE 3CONNECTIONS FOR COUNTING EFFICIENCY DETERMINATIONMETHOD 1. . 13 FIGURE 4CONNECTIONS FOR COUNTING EFFICIENCY DETERMINATION METHOD 2. . 16 FIGURE 5PULSE DISTRIBUTION M ETHOD A. . 18 FIGURE 6PULSE DISTRIBUTION M ETHOD B. . 1

10、9 FIGURE B1STANDARD DEVIATION DIAGRAM 29 FIGURE B2EFFECT OF DIFFERENTIAL NONLINEARITY. . 30 FIGURE C1ERLENMEYER FLASK MIXING CHAMBER. 33 FIGURE D1OPC FLOW CALIBRATION PLOT. 35 FIGURE D2COINCIDENCE LOSS. . 37 4 IEST 2010 All rights reserved Institute of Environmental Sciences and Technology IEST-RP-C

11、C014.2 TABLE 1OBSERVED COUNT AND 95% UCL. 11 D1CALIBRATION MEASUREMENTS. 34 D2PARTICLE SIZE SELECTION. . 35 D3COUNTING EFFICIENCY DETERMINATION. 36 D4PARTICLE SIZE SELECTION. . 36 D5COUNTING EFFICIENCY DETERMINATION. 37 D6DETERMINATION OF CONCENTRATION LIMIT. 37 APPENDIX AFORMS 21 BPHILOSOPHY. 28 CS

12、PECIFIC IMPLEMENTATIONS OF TEST APPARATUS . 31 DEXAMPLES 34 EBIBLIOGRAPHY 38 IEST-RP-CC014.2 Institute of Environmental Sciences and Technology IEST 2010 All rights reserved 5 Institute of Environmental Sciences and Technology Contamination Control Division Recommended Practice 014.2 Calibration and

13、 Characterization of Optical Airborne Particle Counters IEST-RP-CC014.2 1 SCOPE AND LIMITATIONS 1.1 Scope This Recommended Practice (RP) covers proce-dures for calibrating and characterizing the perfor-mance of optical particle counters (OPCs) that detect and measure the size of single particles in

14、air and other gases. These procedures are intended for use by OPC manufacturers, specialized test houses, and OPC users who maintain calibration and testing facilities to determine the sizing and counting accu-racy of these instruments. 1.2 Limitations The procedures for characterization and calibra

15、tion described in this document use monodisperse particles. The response of actual contamination particles, typi-cally with refractive indices different from the mono-disperse particles used for calibration, will differ slightly from the results obtained from the procedures in this document. Also, t

16、he differences will vary for particle counters with different optical designs. This RP does not discuss calibration of condensation nucleus counters (CNCs). The document assumes CNCs used as reference counters have 100% count-ing efficiency in the range of interest for OPCs. NOTE: This RP does not p

17、urport to address all of the safety issues that may arise from its use. The user is responsible for assessing potential safety issues asso-ciated with a given method at its point of use. Before using the methods described herein, the user should consider all general laboratory safety precautions. In

18、 particular, the user should identify and implement suitable health and safety measures and comply with all applicable regulations. 2 REFERENCES The following documents are incorporated into this RP to the extent specified herein. Users should apply the most recent editions of the references. 2.1 Re

19、ference Documents IEST-RD-CC011.2: A Glossary of Terms and Defini-tions Related to Contamination Control IEST-RP-CC013: Calibration Procedures and Guidelines for Select Equipment Used in Testing Cleanrooms and Other Controlled Environments ISO 21501-4: Determination of particle size distribu-tionSin

20、gle particle light-interaction methods Part 4: Light-scattering airborne particle counter for clean spaces 2.2 Sources and Addresses IEST Institute of Environmental Sciences and Technology 2340 S. Arlington Heights Road, Suite 100 Arlington Heights, IL 60005-4516, USA Phone: 847-981-0100 Fax: 847-98

21、1-4130 www.iest.org ISO International Organization for Standardization 1, ch. de la Voie-Creuse, Case postale 56 CH-1211 Geneva 20, Switzerland Phone: +41 22 749 01 11 Fax: +41 22 733 34 30 www.iso.ch 6 IEST 2010 All rights reserved Institute of Environmental Sciences and Technology IEST-RP-CC014.2

22、3 TERMS AND DEFINITIONS The following terms have special meaning in the con-text of this RP. See also IEST-RD-CC011. calibration The comparison of a measurement standard or in-strument of unknown accuracy with another standard or instrument of known accuracy to detect, correlate, report, or eliminat

23、e by adjustment any variation in the accuracy of the unknown standard or instrument. coefficient of variation A measure of the width of a distribution, expressed as a percentage, obtained by dividing the standard devia-tion of the distribution by the mean of the distribution. coincidence The presenc

24、e of two or more particles in the sensing volume of the instrument at the same time, causing the instrument to interpret the combined signal erro-neously as resulting from one larger particle. concentration The number of particles per unit volume at ambient temperature and pressure. concentration li

25、mit The particle concentration specified by the manufac-turer at which the error due to coincidence is 10% or less. (Manufacturers may specify concentration limits at error levels other than 10%.) counting efficiency The ratio, expressed as a percentage, of a detected concentration of monodisperse p

26、articles divided by the actual concentration of particles of a given size or range of sizes. false count The maximum particle count indicated by a particle counter, in a given volume, that is sampling particle-free air. This value is specified by the manufacturer, and commonly is also referred to as

27、 false call rate, false count, noise, or noise level. inlet flow The gas that enters the optical particle counter (OPC) through the gas inlet. Flow rate is expressed as vo-lume per unit time, at ambient temperature and pres-sure. (See also sample flow.) lower counting limit The smallest particle siz

28、e, specified by the manufac-turer, at which the OPC is capable of 50% counting efficiency. monodisperse particles Polymer spheres composed of polystyrene or a simi-lar polymer, sometimes abbreviated “PSL,” having a refractive index of 1.581.61 and a distribution in which the coefficient of variation

29、 is 5% or less when suspended in liquid. When dry particle standards are used, the allowed coefficient of variation should be as low as possible, but may be as high as 15%. See also polymer microspheres (PSL). most penetrating particle size (MPPS) The particle size at which a given filter has its hi

30、ghest penetration (or lowest efficiency); i.e., the worst-case particle size with respect to filtration efficiency. From filtration theory, efficiency is higher for par-ticle sizes smaller or larger than the MPPS. In prac-tice, the MPPS of a filter is considered to be within a measured size range ty

31、pical in commercial instru-ments rather than at one unique particle size. NMI A term referring to a national metrology institute (e.g., NIST (US), NPL (United Kingdom), PTB (Germany), or AIST (Japan). optical particle counter (OPC) A light-scattering instrument with display or record-ing means to co

32、unt and size discrete particles in air and other gases. particle size For calibration, the mean diameter of the monodis-perse particles. For applications, the diameter of a reference sphere having known properties and pro-ducing the same response in the OPC as the particle being measured. polymer mi

33、crospheres (PSL) A term referring to a common type of highly uniform spheres (or a suspension thereof) used for characteriz-ing and calibrating an OPC. (See also monodisperse particles.) resolution A measure of the ability of a particle counter to diffe-rentiate between particles of different sizes;

34、 also, the range of sizes an instrument would ascribe to a particu-lar particle if its size were determined repeatedly. response rate A measure of the time a particle counter takes to re-cover from exposure from a high-particulate concen-tration to that of a particle-free condition. NOTE: If the air

35、flow movement characteristics through the optics chamber are poor, residual particles may result in an extended response rate. Sedimentation of residual par-ticles may cause contamination of the sensor. sample flow The gas that passes through the sensing volume of the particle counter. The sample fl

36、ow may be a portion of the inlet flow. Flow rate is expressed as volume per IEST-RP-CC014.2 Institute of Environmental Sciences and Technology IEST 2010 All rights reserved 7 unit time, at ambient temperature and pressure. (See also inlet flow.) sensing volume The portion of the illuminated region t

37、hrough which the aerosol passes and from which scattered light is collected by the detector. 4 BACKGROUND AND PURPOSE This RP provides standardized test procedures to calibrate and characterize the performance of optical particle counters. OPCs are used to define airborne particle size distribution

38、and concentrations in air and other non-hazardous gases. The data obtained from these instruments are used to verify cleanroom and clean device classification, to characterize air filter performance, to verify installed filter system integri-ty, and to characterize particle emissions from poten-tial

39、 contamination sources. It is often necessary or desirable to use different OPCs operating at different locations or different OPCs at the same location at different times. OPCs of different design may not produce the same data from identical gas samples. Such discrepancies may occur even with simil

40、ar OPCs if calibrated differently. For these reasons, a standardized calibration methodology should be es-tablished to minimize variability among different OPCs. The procedures in this RP are voluntary, not required, and should be used in conjunction with an agreement between customer and supplier c

41、onsider-ing the requirements of ISO 21501-4. The procedures defined in this RP include: Calibration of inlet flow rate (section 6) Particle size calibration (section 7) False count (section 8) Counting efficiency (sections 9 and 10) Response rate (section 11) Concentration (coincidence) limit (secti

42、on 12) Resolution (section 13) 5 REQUIREMENTS 5.1 Materials and equipment The following equipment may be needed to perform the measurements described in this document. Forms for recording test data may be found in Appendix A. Section 6Calibration of inlet flow rate Flowmeter Tubing, hose clamps, or

43、fittings Stop watch Thermometer Barometer Section 7Particle size calibration Monodisperse particles (NMI traceable) Diluent Aerosol generator Oscilloscope Pulse height analyzer Section 8False count Filter Section 9Counting efficiency; Method 1 Monodisperse particles Aerosol generator Aerosol size se

44、parator Mixing chamber Tubing Reference counter/CNC Section 10Counting efficiency, Method 2 Monodisperse particles Aerosol generator Mixing chamber Tubing Reference counterOPC certified by the pri-mary method (section 9) Section 11Response rate Filter Monodisperse particles Diluent Aerosol generator

45、 Section 12Concentration (coincidence) limit Same as for section 9 Section 13Resolution Same as for section 7 5.2 Concentration of particles For all tests described in this RP (unless otherwise noted), the concentration of particles should be no more than 25% of the concentration limit specified by

46、the manufacturer of the instrument. 5.3 Environment The calibration and characterization of the OPC should be performed in a controlled environment (temperature, humidity, vibration). The degree of environmental control necessary should take into 8 IEST 2010 All rights reserved Institute of Environm

47、ental Sciences and Technology IEST-RP-CC014.2 account the operational specification of all instru-ments used. 5.4 Initial setup and warm-up of the OPC Before performing any procedure, confirm that the OPC is turned on and the operating parameters of the OPC are set to the standard settings or the va

48、lues recommended in this document. Allow time for the instrument to warm up as specified by the manufac-turer or for a minimum of 30 min. 6 CALIBRATION OF INLET FLOW RATE 6.1 Apparatus and materials The following equipment may be needed to perform the measurements described in this document. Forms f

49、or recording test data may be found in Appendix A. 6.1.1 Flowmeter A flowmeter allows the determination of the flow rate in the sample inlet of the OPC. The accuracy of the flowmeter should be 3% of full scale or better. The flowmeter should have been calibrated within the time schedule specified in IEST-RP-CC013. The pressure drop of the flowmeter should be sufficiently small that it does not introduce an error greater than 1% in the nominal flow rate due