1、Designation: D 3796 90 (Reapproved 2004)Standard Practice forCalibration of Type S Pitot Tubes1This standard is issued under the fixed designation D 3796; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A
2、 number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers the determination of Type S pitottube coefficients in the gas velocity range from 305 to 1524m/min or 5.08 to 25
3、.4 m/s 1000 to 5000 ft/min. The methodapplies both to the calibration of isolated Type S pitot tubes(see 5.1), and pitobe assemblies.1.2 This practice outlines procedures for obtaining Type Spitot tube coefficients by calibration at a single-velocity settingnear the midpoint of the normal working ra
4、nge. Type S pitotcoefficients obtained by this method will generally be valid towithin 63 % over the normal working range. If a more precisecorrelation between Type S pitot tube coefficient and velocityis desired, multivelocity calibration technique (Annex A1)should be used.1.3 This practice may be
5、used for the calibration of thermalanemometers for gas velocities in excess of 3 m/s 10 ft/s.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health prac
6、tices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Document2.1 ASTM Standards:2D 1356 Terminology Relating to Sampling and Analysis ofAtmospheres3. Terminology3.1 For definitions of terms used in this test method, refer toTerminology D 1356.3.2 Definitions:3.
7、2.1 isolated Type S pitot tubeany Type S pitot tube thatis calibrated or used alone (Fig. 1).3.2.2 normal working velocity rangethe range of gasvelocities ordinarily encountered in industrial smokestacks andducts: approximately 305 to 1524 m/min or 5.08 to 25.4 m/s1000 to 5000 ft/min.3.2.3 pitobe as
8、semblyany Type S pitot tube that is cali-brated or used while attached to a conventional isokineticsource-sampling probe (designed in accordance with Martin(1)3or allowable modifications thereof; see also Fig. 7).4. Summary of Practice4.1 The coefficients of a given Type S pitot tube aredetermined f
9、rom alternate differential pressure measurements,made first with a standard pitot tube, and then with the Type Spitot tube, at a predetermined point in a confined, flowing gasstream. The Type S pitot coefficient is equal to the product ofthe standard pitot tube coefficient, Cp(std), and the square r
10、ootof the ratio of the differential pressures indicated by thestandard and Type S pitot tubes.5. Significance and Use5.1 The Type S pitot tube (Fig. 1) is often used to measurethe velocity of flowing gas streams in industrial smokestacksand ducts. Before a Type S pitot tube is used for this purpose,
11、its coefficients must be determined by calibration against astandard pitot tube (2).6. Apparatus6.1 Flow SystemCalibration shall be done in a flowsystem designed in accordance with the criteria illustrated inFig. 2 and described in 6.1.1 through 6.1.5.6.1.1 The flowing gas stream shall be confined w
12、ithin adefinite cross-sectional area; the cross section shall be prefer-ably circular or rectangular (3). For circular cross sections, theminimum duct diameter shall be 305 mm 12 in. Forrectangular cross sections, the width shall be at least 254 mm10 in. Other regular cross-section geometries (for e
13、xample,hexagonal or octagonal) are permissible, provided that theyhave cross-sectional areas of at least 645 cm2100 in.2.6.1.2 It is recommended that the cross-sectional area of theflow-system duct be constant over a distance of 10 or moreduct diameters. For rectangular cross sections, use an equiva
14、-lent diameter, calculated as follows, to determine the numberof duct diameters:1This practice is under the jurisdiction of ASTM Committee D22 on Samplingand Analysis of Atmospheres and is the direct responsibility of SubcommitteeD22.01 on Quality Control.Current edition approved October 1, 2004. Pu
15、blished December 2004. Originallyapproved in 1979. Last previous edition approved in 1998 as D 3796 - 90 (1998).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the
16、standards Document Summary page onthe ASTM website.3The boldface numbers in parentheses refer to the list of references at the end ofthis practice.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.De5 2LW/L 1 W! (1)where:De= equivalent
17、 diameter,L = length of cross section, andW = width of cross section.For regular polygonal ducts, use an equivalent diameter,equal to the diameter of the inscribed circle, to determine thenumber of duct diameters.6.1.3 To ensure the presence of stable, well-developed flowpatterns at the calibration
18、site (test section), it is recommendedthat the site be located at least 8 duct diameters (or equivalentdiameters) downstream and 2 diameters upstream from thenearest flow disturbances. If the 8 and 2-diameter criteriacannot be met, the existence of stable, developed flow at thetest site must be adeq
19、uately demonstrated.6.1.4 The flow-system fan shall have the capacity to gener-ate a test-section velocity of about 909 m/min or 15.2 m/s3000 ft/min; this velocity should be constant with time. Thefan can be located either upstream (Fig. 2) or downstream fromthe test-section.6.1.5 Two entry ports, o
20、ne each for the Type S and standardpitot tubes, shall be cut in the test section. The standard pitottube entry port shall be located slightly downstream of theType S port, so that the standard and Type S impact openingswill lie in the same plane during calibration. To facilitatealignment of the pito
21、t tubes during calibration, it is advisablethat the test section be constructed of acrylic or similartransparent material.6.2 Standard Pitot Tube, used to calibrate the Type S pitottube. The standard pitot tube shall have a known coefficient,obtained preferably directly from the National Institute o
22、fStandards and Technology in Gaithersburg, MD. Alternatively,a modified ellipsoidal-nosed pitot static tube, designed asshown in Fig. 3 may be used (4). Note that the coefficient of theellipsoidal-nosed tube is a function of the stem/static holedistance; therefore, Fig. 4 should be used as a guide f
23、ordetermining the precise coefficient value.6.3 Type S Pitot Tube, (isolated pitot or pitobe assembly)either a commercially available model or constructed inaccordance with Martin (1) or allowable modifications thereof.6.4 Differential Pressure GageAn inclined manometer, orequivalent device, shall b
24、e used to measure differential pres-sure. The gage shall be capable of measuring DP to within60.13 mm water or 1.2 Pa 60.005 in. water.6.5 Pitot LinesFlexible lines, made of poly(vinyl chlo-ride) (or similar material) shall be used to connect the standardand Type S pitot tubes to the differential-pr
25、essure gage.7. Procedure7.1 Assign a permanent identification number to the Type Spitot tube. Mark or engrave this number on the body of thetube. Mark one leg of the tube “A,” and the other, “B.”7.2 Prepare the differential-pressure gage for use. If aninclined manometer is to be used, be sure that i
26、t is properlyfilled, and that the manometer fluid is free of contamination.7.3 Level and zero the manometer (if used). Inspect all pitotlines and check for leaks; repair or replace lines if necessary.7.4 Turn on the flow system fan and allow the flow tostabilize; the test section velocity should be
27、about 909 m/minor 15.2 m/s 3000 ft/min. Seal the Type S entry port.7.5 Determine an appropriate calibration point. Use thefollowing guidelines:7.5.1 For isolated Type S pitot tubes (or pitot tube-thermocouple combinations), select a calibration point at ornear the center of the duct.7.5.2 For pitobe
28、 assemblies, choose a point for which probeblockage effects are minimal; the point should be as close tothe center of the duct as possible. To determine whether a givenpoint will be acceptable for use as a calibration point, make aprojected-area model of the pitobe assembly (Fig. 5), with theimpact
29、openings of the Type S pitot tube centered at the point.For assemblies without external sheaths (Fig. 5(a), the pointwill be acceptable if the theoretical probe blockage, calculatedas shown in Fig. 5, is less than or equal to 2 %. For assembliesFIG. 1 Isolated Type-S Pitot TubeFIG. 2 Pitot Tube Cali
30、bration SystemD 3796 90 (2004)2with external sheaths (Fig. 5(b), the point will be acceptable ifthe theoretical probe blockage is 3 % or less (5).7.6 Connect the standard pitot tube to the differential-pressure gage. Position the standard tube at the calibrationpoint; the tip of the tube should be p
31、ointed directly into theflow. Particular care should be taken in aligning the tube, toavoid yaw and pitch angle errors. Once the standard pitot tubeis in position, seal the entry port surrounding the tube.7.7 Take a differential-pressure reading with the standardpitot tube; record this value in a da
32、ta table similar to the oneshown in Fig. 6. Remove the standard pitot tube from the ductand disconnect it from the differential pressure gage. Seal thestandard pitot entry port.7.8 Connect the Type S pitot tube to the differential-pressuregage and open the Type S entry port. Insert and align the Typ
33、eS pitot tube so that its “A” side impact opening is positioned atthe calibration point, and is pointed directly into the flow. Sealthe entry port surrounding the tube.7.9 Take a differential-pressure reading with the Type Spitot tube; record this value in the data table. Remove the TypeS pitot tube
34、 from the duct; disconnect the tube from thedifferential-pressure gage. Seal the Type S entry port.7.10 Repeat procedures 7.6 through 7.9, until three pairs ofdifferential-pressure readings have been obtained.7.11 Repeat procedures 7.6 through 7.10 above for the “B”side of the Type S pitot tube.7.12
35、 For pitobe assemblies in which the free space betweenthe pitot tube and nozzle (dimension x, Fig. 7) is less than 19.0mm (34 in.) with a 12.7-mm 12-in. inside diameter samplingnozzle in place, the value of the Type S pitot tube coefficientwill be a function of the free space, which is, in turn, dep
36、endentupon nozzle size (6); therefore, for these assemblies, a separatecalibration should be done, in accordance with procedures 7.6through 7.11, with each of the commonly used nozzle sizes inplace. Single-velocity calibration at the midpoint of the normalworking range is suitable for this purpose (
37、7), even thoughnozzles larger than 6.35-mm 14-in. inside diameter are notordinarily used for isokinetic sampling at velocities around 909m/min or 15.2 m/s 3000 ft/min.8. Calculation8.1 Calculate the value of the Type S pitot tube coefficientfor each of the six pairs of differential-pressure readings
38、 (threefrom side A and three from side B), as follows:Cps!5Cpstd!DPstdDPs(2)where:Cp(s) = Type S pitot tube coefficient,Cp(std) = coefficient of standard pitot tube,DPstd= differential pressure measured by standard pitottube, kPa (in. H2OormmH2O), andDPs= differential pressure measured by Type S pit
39、ottube, kPa (in. H2OormmH2O).8.2 Calculate the mean A and B side coefficients of the TypeS pitot tube, as follows:CpsideAorB!5S13Cps!3(3)where:Cp(side A or B) = mean A or B side coefficient, andCp(s) = individual value of Type S pitot coef-ficient, A or B side.8.3 Subtract the mean A side coefficien
40、t from the mean Bside coefficient. Take the absolute value of this difference.FIG. 3 Ellipsoidal Nosed Pitot-Static TubeD 3796 90 (2004)38.4 Calculate the deviation of each of the A and B sidecoefficient values from its mean value, as follows:Deviation A or B side!5Cps!2CpsideAorB! (4)8.5 Calculate
41、the average deviation from the mean, for boththe A and B sides of the pitot tube, as follows:ssideAorB!5S13Cps!2CpsideAorB!#3(5)where s(sideAor B) = average deviation of Cp(s) values fromthe mean, A or B side.FIG. 4 Effect of Stem/Static Hole Distance on Basic Coefficient, Cp(std), of Standard Pitot
42、-Static Tubes with Ellipsoidal NoseFIG. 5 Projected-Area Models for Typical Pitobe AssembliesD 3796 90 (2004)49. Precision and Bias9.1 PrecisionThe results of the calibration should not beconsidered suspect unless the following criteria fail to be met:9.1.1 The absolute value of the difference betwe
43、en the meanA and B side coefficients (see 8.3) is less than or equal to 0.01.9.1.2 The A and B side values of average deviation are lessthan or equal to 0.01.NOTE1 in. H2O = 0.249 kPa; 1 mm H2O = 0.0098 kPa.FIG. 6 Calibration Data Table, Single-Velocity CalibrationNOTEThis figure shows pitot tube-no
44、zzle separation distance (x); the Type S pitot tube coefficient is a function of x, if x 34 in. where Dn=12 in.FIG. 7 Typical Pitobe Assemblymm in.1312193476 3D 3796 90 (2004)59.1.3 If criterion 9.1.1,or9.1.2, or both, are not met, theType S pitot tube may not be suitable for use. In such cases,repe
45、at the calibration procedure two more times; do not use theType S pitot tube unless both of these runs give satisfactoryresults.9.2 BiasIn general, the mean A and B side coefficientvalues obtained by this method will be accurate to within63 % over the normal working range (7).9.2.1 When a calibrated
46、 pitobe assembly is used to measurevelocity in ducts having diameters (or equivalent diameters)between 305 and 915 mm 12 and 36 in., the calibrationcoefficients may need to be adjusted slightly to compensate forprobe blockage effects. A procedure for making these adjust-ments is outlined inAnnexA2.
47、Conventional pitobe assembliesare not recommended for use in ducts smaller than 305 mm 12in. in diameter.9.2.2 AType S pitot tube shall be calibrated before its initialuse. Thereafter, if the tube has been significantly damaged byfield use (for example, if the impact openings are noticeablybent out
48、of shape, nicked, or misaligned), it should be repairedand recalibrated. The data collected should be evaluated in thelight of this recalibration.9.2.3 The coefficient of a calibrated isolated Type S pitottube may change if the isolated tube is attached to a sourcesampling probe and used as a pitobe
49、 assembly. The isolated andassembly coefficient values can only be considered equal whenthe intercomponent spacing requirements illustrated in Figs.8-10 and are met.10. Keywords10.1 calibration; pitot tube; Type S pitot tubeFIG. 8 Minimum Pitot-Nozzle Separation Needed to Prevent Aerodynamic Interferencemm in.1312193476 3D 3796 90 (2004)6ANNEXES(Mandatory Information)A1. PROCEDURE FOR MULTIVELOCITY CALIBRATION OF TYPE S PITOT TUBESA1.1 ScopeA1.1.1 See 1.1.A1.2 Referenced DocumentsA1.2.1 See 2.1.A1.3 DefinitionsA1.3
