1、Designation: D 5089 95 (Reapproved 2008)Standard Test Method forVelocity Measurements of Water in Open Channels withElectromagnetic Current Meters1This standard is issued under the fixed designation D 5089; the number immediately following the designation indicates the year oforiginal adoption or, i
2、n the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the use of single-axis ordual-axis electromagnetic current
3、 meters for the measurementof water velocities in open channels.1.2 This test method covers only these components andappurtenances of portable open-channel current-meter systems,which are customarily required when an operator is in atten-dance.1.3 The values stated in inch-pound units are to be rega
4、rdedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.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
5、 of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1129 Terminology Relating to WaterD 2777 Practice for Determination of Precision and Bias ofApplicable Test Met
6、hods of Committee D19 on WaterD 3858 Test Method for Open-Channel Flow Measurementof Water by Velocity-Area MethodD 4409 Test Method for Velocity Measurements of Water inOpen Channels with Rotating Element Current Meters2.2 ISO Standards:3ISO 3454 Liquid Flow Measurement in Open ChannelsSounding and
7、 Suspension EquipmentISO 3455 Liquid Flow Measurement in Open ChannelsCalibration of Rotating Element Current Meters inStraight Open Tanks3. Terminology3.1 Definitions: For definitions of terms used in this testmethod refer to Terminology D 1129.3.2 Definitions of Terms Specific to This Standard:3.2
8、.1 boundary layera relatively thin layer of viscousinfluence adjacent to the probe (or any solid) surface caused bythe requirement that the water velocity must be zero at the wall.3.2.2 cosine responsethe ability of a meter, placed at anangle to the oncoming flow, to sense the component of velocityp
9、arallel to its axis.3.2.3 turbulenceirregular condition of flow in which thevarious quantities show a random variation with time and spacecoordinates so that statistically distinct average values can bediscerned.4. Summary of Test Method4.1 Electromagnetic liquid flow current meters are based onthe
10、Faraday principle of electromagnetic induction, whichstates that voltage is proportional not only to flow speed butalso to the magnetic flux density and the distance betweenelectrodes. In the application of the electromagnetic liquidcurrent meter, a conductor (water) moving in a magnetic field(creat
11、ed from within the sensor) generates a voltage that isproportional to the rate of flow of water through the magneticfield. This variable voltage lies in a plane that is perpendicularto both the water velocity vector and the magnetic field vectorand is sensed by pairs of electrodes.5. Significance an
12、d Use5.1 This test method is particularly used for measuring thevelocity at a point in an open channel as part of a velocity-areatraverse to determine the flowrate of water. To this end it1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Su
13、bcommittee D19.07 on Sediments, Geomor-phology, and Open-Channel Flow.Current edition approved Oct. 1, 2008. Published November 2008. Originallyapproved in 1990. Last previous edition approved in 2003 as D 5089 95 (2003).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact
14、 ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3“Measurement of Liquid Flow in Open Channels,” ISO Standards Handbook16, 1983.Available fromAmerican National Standards Institute (ANSI), 2
15、5 W. 43rdSt., 4th Floor, New York, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.should be used in conjunction with Test Method D 3858.Asingle axis probe with cosine response will suffice for most ofthe
16、se applications.5.2 This test method is also useful in applications where thevelocity itself (rather than a volumetric flowrate) is the desiredend product.6. Interferences6.1 As with any intrusive flow measuring device, electro-magnetic current meter sensors may be fouled by pieces ofdebris of the t
17、ype that can cling to or wrap around the sensorwhich could affect measurement accuracy, and sensors may bedamaged by heavy debris in very high velocity flow.6.2 Electromechanical flow sensors can be affected by oil orother materials coating the sensor.6.3 Electromagnetic flow sensors can be affected
18、 by exter-nal electrical noise such as that caused by nearby heavyelectrical equipment, and by voltage gradients caused bynearby galvanic corrosion, or nearby power lines. Cables andconnectors should be properly shielded to reduce noise prob-lems.6.4 Although electromagnetic velocity meters are in p
19、rin-ciple capable of measuring substantially lower velocities thanrotating element current meters, measurement of near-zerovelocities may be hampered by noisy output signals caused byspurious electrical and magnetic noise, by fouling, by zero-drift, and by calibration uncertainties. Where external e
20、lectricalnoise creates uncertainty in sensed velocities, the electromag-netic meter may not be the appropriate velocity instrument forthe site.7. Apparatus7.1 Electromagnetic Current Meter:7.1.1 The current meter consists of an electromagnet togenerate a magnetic field perpendicular to the flow to b
21、emeasured, electrodes to sense the generated voltage, a housingor supporting structure, and a voltage readout. The sensor canhave either one pair of electrodes or two orthogonal pairs ofelectrodes depending upon whether it is a single-axis ormulti-axis instrument.7.1.2 The current meter must have a
22、self-contained powersource for the electromagnet and for any other electricalcomponents. This power source must have sufficient durationfor normal field-work requirements. The power cells shall beeither rechargeable or readily replaceable by an operator in thefield.7.1.3 The readout may be either in
23、 terms of electrical unitsor directly in velocity. If the former, the manufacturer mustsupply convenient velocity conversion tables with the instru-ment. Readouts may be either analog or digital with a readoutcapability of giving velocity accurate to 60.01 ft/s (0.305cm/s).7.1.4 Optionally the curre
24、nt meter system may include achart recorder or other type of data recording, storage ortransmission device in parallel with the manual readout. One ofthese options is required only if the current meter is to be usedunattended. Specifications for these devices are beyond thescope of this test method.
25、7.1.5 Optionally the current-meter system may includedirection-sensing equipment. Specifications for this equipmentare beyond the scope of this test method.7.1.6 The current meter shall include a means by which theuser can check its internal operation. However, it is empha-sized that checks of this
26、type do not constitute full calibrations.7.1.7 All components of the current-meter system shall bemade of materials that have corrosion resistance consistentwith the intended application. Fabrication material must beselected to preclude galvanic corrosion, which could createelectronic interference a
27、nd degrade accuracy readings of thedevice.7.1.8 The manufacturer must inform the user of any limitson ambient temperature, depth, velocity, or other parametersbeyond which the instrument should not be used.7.2 Suspension:7.2.1 The current meter can be suspended in the channeleither rigidly, referred
28、 to herein as rod mounting, or flexibly, asby cable and weight or other type of mooring. As a minimum,current meters intended for open-channel use shall be equippedwith appropriate fittings for either rod mounting or cablesuspension; but it is preferable that general purpose currentmeters be adaptab
29、le to both types of suspension. The cableshould be adequate to support sounding weights and also beproperly electronically shielded to prevent interference withoperation of the meter or transmission of signals from meter toreadout equipment, or both.7.2.2 The rating of a current meter may depend upo
30、n thegeometry of the suspension system in the immediate vicinity ofthe velocity sensor. Therefore, if the manufacturer does notfurnish the suspension system with which the meter wascalibrated, he shall provide all specifications necessary for theuser to mount the meter in a manner consistent with it
31、scalibration.7.2.3 Although “rod mounting” can describe any rigidsuspension, in this context it frequently refers to a rod heldvertically against the channel bottom by an operator standingover a small channel (or wading in a larger channel). Theconnection for rod mounting shall provide, in conjuncti
32、on withthe rod, rigidity and vibration-free performance at the highestvelocity claimed for the meter, and shall provide for adjustablesensor position (depth) along the rod. The rod diameter shall bein the range of 0.5 to 1.0 in. (12.7 to 25.4 mm).7.2.4 Although cable suspension can describe any flex
33、iblemooring, in this context it frequently refers to a (nearly)vertical cable which is weighted at its end and which can bewinched to place the current sensor at any desired depth.Descriptions of and requirements for suspension equipmentappropriate for stream gaging are available in ISO 3454. Thiste
34、st method includes only those elements which directly affectthe current-meter performance.7.2.4.1 The connection between the sensor and cable mustpermit the sensor to assume its normal operational position.The sensor must be stable with respect to the flow and be ableto maintain its proper attitude;
35、 this can be accomplished bydesign of sensor shape, use of fins, or by other means. IfD 5089 95 (2008)2detachable fins or other appurtenances are provided, themanufacturer must provide calibrations both with and withoutthis equipment.7.2.4.2 The weight used in a cable-and-weight suspensionshould be
36、heavy enough to avoid excessive downstreamdeflection of the cable, particularly in deep and swift waters. Ifsome deflection is unavoidable, tables for air-line and wet-linecorrections are available.4The weights should offer minimalresistance to the flow and should be able to maintain a stableand lev
37、el position. They should be so shaped and placed thatthe current meter is not affected by eddies shed by the weight,blockage, or other instabilities.7.2.4.3 It is preferable that the weight be mounted below thecurrent meter. This permits the weight to serve as a soundingdevice for depth determinatio
38、n and as protection for the sensor.The suspension cable should be reverse wound to avoidspinning of the immersed current meter and weight.8. Sampling8.1 Sampling, as defined in Terminology D 1129,isnotapplicable in this test method. Sampling to obtain averagevelocities in a cross section for purpose
39、 of flowrate determi-nation is covered in Test Method D 3858.9. Calibration9.1 Calibrate each electromagnetic current meter individu-ally in water over the expected operating range of velocity thatthe meter will be used. Recalibration intervals will dependupon experience with specific instruments an
40、d applications. Ageneral guideline would be to recalibrate a new instrumentbefore the start of a “field season,” or every 200 h of usage.Recalibrations must be performed at any time that data appearsto be doubtful or repairs are made.9.2 Calibrations must be made with the suspension in theimmediate
41、vicinity of the sensor identical to that which will beused in the field, unless it can be shown that the differences donot affect the rating.9.3 The manufacturer must supply an estimate of the accu-racy and precision of the rating, along with the method ofcalibration (towing tank or water flow facil
42、ity) and informationon cosine response in azimuth and tilt, as appropriate.9.4 Details on calibration requirements may be found inISO 3455 and in Test Method D 4409.10. Procedure10.1 Check the internal electrical performance (7.1.6) andin-situ zero (11.4.1), and clean the electrodes and sensor, atin
43、tervals determined by experience. In the absence of otherguidelines it is recommended that these procedures be done atleast daily. Follow manufacturers instructions to avoid dam-age by frequent cleaning. Avoid application of oil or heavyhydrocarbons to electrodes.10.2 For velocity-area traverses ref
44、er to Practice D 3858 forinformation on velocity sampling point and sampling times.However, the meter must be capable of averaging velocity overa 40 to 70 s period to account for pulsations in the water flow.10.2.1 If a rod suspension is used with an electromagneticcurrent meter with cosine response
45、, orient the current meter tomeasure the flow perpendicular to the cross section. Even if theflow at that measuring station is not perpendicular to the crosssection, no errors will occur since the instrument (provided itscosine response is adequate) will detect the perpendicularcomponent.10.2.2 If a
46、 cable-and-weight suspension is used and the flowis not perpendicular to the cross section, independently deter-mine the angle of the current with respect to the perpendicularand multiply the measured velocities by the cosines of theangles so determined.10.3 Users must develop, through trials, infor
47、mation such asrequired warm-up time, water-acclimatization time, batterylife, and charging frequency for the instrument, if recom-mended values are not furnished by the manufacturer.11. Precision and Bias11.1 Determination of the precision and bias for this testmethod is not possible, both at the mu
48、ltiple and single operatorlevel, due to the high degree of instability of open channel flow.Both temporal and spatial variability of the boundary and flowconditions do not allow for a consent standard to be used forrepresentative sampling. A minimum bias, measured underideal conditions, is directly
49、related to the bias of the equipmentused and is listed in the following sections. A maximumprecision and bias cannot be estimated due to the variability ofthe sources of potential errors listed in 11.3 and 11.4 and thetemporal and spatial variability of open-channel flow. Anyestimate of these errors could be very misleading to the user.11.2 In accordance with 1.6 of Practice D 2777, an exemp-tion to the precision and bias statement required by PracticeD 2777 was recommended by the results advisor and concurredwith by the Technical Operations Section of the CommitteeD-19 Execu
