1、Designation: E 556 95 (Reapproved 2006)Standard Test Method forCalibrating a Wheel Force or Torque Transducer Using aCalibration Platform (User Level)1This standard is issued under the fixed designation E 556; the number immediately following the designation indicates the year oforiginal adoption or
2、, in the case of revision, the year of last revision. A 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 test method covers the calibration of the force (ortorque) transducer and
3、 associated instrumentation of a mountedtest wheel by using a calibration platform.1.2 This test method is a static calibration, simulating thetraction force between a tire and the pavement.1.3 In the case of a force-measuring system, the instrumen-tation readout is directly proportional to the cali
4、bration forceinput.1.4 In the case of a torque-measuring system, the instru-mentation readout is a measure of the calibration force inputand the effective tire radius.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of
5、the user 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:2E 274 Test Method for Skid Resistance of Paved SurfacesUsing a Full-Scale TireF 377 Practice for Calibrat
6、ion of Braking/Tractive Measur-ing Devices for Testing Tires3. Terminology3.1 Description of Terms:3.1.1 calibration platforma moving platform for applyinga force in the contact plane of a tire, and associated means formeasuring the applied force. The calibration platform consistsof a rigid plate wi
7、th a high friction surface, in contact with thetire footprint, supported on a frictionless, preferably air, bear-ing. It may also be instrumented to measure vertical forces(loads).3.1.2 calibration reference signalsrepeatable signals inthe range of expected wheel-force transducer system loading.Thes
8、e signals could either be constant voltages or preferablyproduced by a strain-gage calibration shunt resistor.3.1.3 crosstalkthe undesired effect of force readings ap-pearing on an unloaded axis of a transducer while applyingforce to another.3.1.4 horizontal traction (traction)a force acting in ahor
9、izontal axis through the wheel transducer; that is, lockedwheel drag force.3.1.5 hysteresisthe maximum difference between corre-sponding transducer outputs (of the wheel force transducersystem) at increasing and decreasing applied calibration force,expressed as a percentage of full load. Proven outl
10、iers areexcluded.3.1.6 nonlinearitythe maximum deviation of the trans-ducer output(s) (of the wheel force transducer system) from thebest-fit linear relation to the applied calibration force, ex-pressed as a percentage of full scale. Proven outliers areexcluded.3.1.7 test wheela wheel and test tire
11、assembly mounted toa test vehicle by means of a force or torque transducer.3.1.8 vertical load (load)force acting in a vertical axisthrough the wheel transducer; that is, weight.3.1.9 wheel force transducer systema force-to-electricalsignal converter system including transducer(s), associatedsignal
12、condition, zeroing, amplifying, recording, and monitor-ing instrumentation.4. Summary of Test Method4.1 The vertical static loads (forces) on the test wheel(s) andhitch are established. If the tester is of the trailer type, it mustbe connected to its tow vehicle. Traction forces are applied tothe lo
13、cked wheel(s) at the tire-platform interface. The calibra-tion platform consists of a bearing that is frictionless in alldirections of the horizontal plane supporting a rigid plate witha high friction surface. The force applied to this platform ismeasured by suitable electronic force transducers.1Th
14、is test method is under the jurisdiction of ASTM Committee E17 onVehicle-Pavement Systems and is the direct responsibility of Subcommittee E17.21on Field Methods for Measuring Tire Pavement Friction.Current edition approved Aug. 1, 2006. Published August 2006. Originallyapproved in 1975. Last previo
15、us edition approved in 2000 as E 556 95 (2000).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 standards Document Summary page onthe ASTM website.1Copyright AST
16、M International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.2 Wheel transducer linearity and hysteresis are deter-mined from an electronic digital meter (x-y chart optional) andare correlated with the tow vehicle instrumentation. Techniquesare given for est
17、ablishing reference signals to be used ascalibration points.4.3 With calibration platforms having force-measurementcapability in the vertical direction, test wheel load (force) isrecorded as a function of the applied tractive calibration force.4.4 With a wheel transducer having normal load (force)-m
18、easuring capability, the transducer output is compared withthe corresponding vertical output of the calibration platform.5. Significance and Use5.1 Wheel force or torque transducers are used underdynamic test conditions, and the measurements are subject tomany error sources. The static calibration r
19、ecommended by thepresent standard cannot eliminate all error sources. Its signifi-cance is in providing an accurate calibration of the transducerand the associated electronics, readout, and recording equip-ment.5.2 Calibration result may be used to either make mechani-cal or electronic adjustments u
20、ntil the readout agrees with thecalibration input. Alternatively, calibration curves or tablesmay be prepared to be used as corrections to measured results.6. Apparatus6.1 The calibration apparatus shall consist of the basiccomponents described below, and calibrated in accordancewith 6.3 of Practice
21、 F 377.6.1.1 A calibration platform for applying tractive forces atthe tire-platform interface of a test wheel, with a calibratedinternal or external reference force transducer to measure theseforces. Capability of measuring vertical forces (wheel loads) isalso desirable.6.1.2 A system for generatin
22、g traction forces appliedthrough the calibration platform.6.1.3 Instrumentation for recording or indicating transduceroutputs, including digital meters and optionally an x-y recorder.6.1.4 Level, tire pressure gage and thermometer.6.1.5 Scale(s) accurate within 0.5 % of maximum expectedaxle load for
23、 the test trailer.7. Preparation of Apparatus7.1 SiteSelect a sheltered, level paved area. (A hardsurface, preferably under cover, is desirable.)7.2 Calibration Platform and Associated InstrumentationPrepare the calibration platform and associated instrumentationby following established set-up proce
24、dures and the manufac-turers manuals where applicable.7.3 Test TiresSet the inflation pressure under normalvertical load (force). Inflation pressure shall be 24.0 6 0.5 psi(165.0 6 3.5 kPa) at ambient temperature (cold).7.4 Traction Tester InstrumentationCheck the test vehicleinstrumentation by foll
25、owing established set-up procedures forthe system with reference to the recommended procedure in themanufacturers manual, where applicable. Set all gains andoffsets at values normally used during friction testing. Recordthe settings.7.4.1 Force-Type TransducerLoad crosstalk into traction:if, with fu
26、ll normal load back on the test wheel, the tractionoutput is different from zero by more than 1 % of the appliednormal load, adjust by either rotating the transducer (ifprovisions for rotation have been made) or by changing thehitch height, that is, tilting the trailer to orient the transducerhorizo
27、ntal axis parallel to the calibration plane. Then apply 500lb of traction force and note the change in load reading. If morethan 1 % crosstalk, check transducer leveling and repeat thistest.7.4.2 Torque Type TransducerUse steps 7.4 and 7.4.1,substituting the torque output for the traction. If the lo
28、ad intotorque crosstalk is greater than 1 % of the applied normal load,refer to the manufacture since there are normally no useradjustments.7.5 Test Trailer Position the trailer coupled to its towvehicle on level ground and set the trailer variables such as tirepressure, hitch height, and inflation
29、pressure of air shockabsorbers where present to the normal operating values.Measure the hitch height from level ground to the center of thehitch. Decouple the trailer and weigh it at each point ofsupport, maintaining its relative level. Correct the weights ifneeded to comply with Test Method E 274.
30、Recouple the trailerto the towing vehicle.NOTE 1The tow vehicle should have12 tank of water, and a full fuelload before leveling the trailer.7.6 Wheel Transducer With the test wheel loaded, thewheel transducer traction output should be adjusted to zero.Then remove 500 lb of the load and recheck trac
31、tion zero.7.7 Record all measures, weights, and dimensions, and thetrailer leveling adjustments that give zero transducer outputs.8. Frequency of Calibration8.1 It is recommended that the system be calibrated accord-ing to all sections of this specification at least once a year.8.2 For routine test
32、to indicate normal system operationsonly, it may be sufficient to abbreviate the procedure in Section9.8.3 Calibration should be performed at least once a monthaccording to 8.2.8.4 The calibration should be performed whenever themeasured test results are inconsistent with previous values fora given
33、test site.9. Procedure9.1 Determine that the calibration platform has been suit-ably calibrated within a reasonable period of time (see 6.1), oneyear.9.2 If the test vehicle is of the trailer type, hitch and align itwith the tow vehicle. The calibration may be performed withauxiliary electrical powe
34、r for the instrumentation. In this case,after completing the calibration, check the system whenpowered by the vehicle electrical system with the enginerunning, to assure that the output(s) have not changed. Thepreparations described in Section 7 shall have been performed.9.3 Place the test wheel(s)
35、on the calibration platform(s)using blocks, if needed, under the other wheels to maintain alevel plane of support for all system tires.E 556 95 (2006)29.4 With the test wheel raised clear of the platform, zero theoutput(s) of the calibration platform in accordance with estab-lished operating procedu
36、res. Zero the wheel transducer out-put(s). (WarningMake sure that wheel brakes do not drag.)9.5 Align the calibration platform(s) and the associatedforce application system(s) with the test tire(s) and lower thetest wheel onto the platform.9.6 The platform shall be level within 60.25 prior to thecal
37、ibration.NOTE 2Increased accuracy may be obtained by maintaining theaforementioned level throughout the calibration procedure.9.7 Record the ambient temperature. To meet this standard,calibration can only be done when the ambient temperature isbetween 40 and 100F (4 and 38C).9.8 Use digital meter(s)
38、 and optionally x-y recorder(s) toobserve the wheel-force transducer system signals at the inputto the system recorder.9.8.1 With the trailer level and with full vertical load andzero traction force applied to the test wheel(s), adjust thesystem vertical load indicator to correspond with the platfor
39、mvertical load value.9.8.2 Lock the test wheel and apply a midrange tractiveforce (typically 500-lbf 2.2 kN) via the platform to the testwheel. Adjust the system traction indicator to correspond withthe platform traction value. Return the traction force to zero.9.9 Record the wheel-transducer vertic
40、al load output and theforce-place transducer vertical output, on both the systemrecorder and meter while increasing and decreasing the verticalforce applied by at least 20 % of the static wheel load value in100 lbf (445 N) increments. This can be done by adding 200 lb(shot bags) to the trailer wheel
41、 load.9.10 Establish the linearity and hysteresis characteristics forthe vertical transducer output, if applicable, using the data in9.9.9.11 Record the wheel transducer output(s) (horizontal trac-tion and vertical load) versus the platform traction and verticalload readings on both the system-recor
42、der and the meter whileincreasing and decreasing the traction force by 100 lbf (445 N)increments through the full calibration range (typically 0 to50 % of vertical load).NOTE 3For a two-wheeled towed test trailer, the test wheel verticalload should decrease linearly from the zero traction value as t
43、he appliedtraction force increases at a slope proportional to the H/L ratio of thetrailer3where H is the initial hitch height and L is the initial hitch-to-axlelength (see Test Method E 274). The non-test wheel vertical load (force)should remain constant at the zero traction value.9.12 If the test w
44、heel load and traction values obtained in9.9 and 9.11 agree with the platform values within 61%,apply system load and traction calibration signals and recordfor the future reference. If differences greater than 1 % arefound, the system may require maintenance or the crosstalkshould be rechecked as d
45、escribed in 7.6.NOTE 4Some calibration platforms use ball or roller bearing (insteadof air bearings). Any side force on the wheel under calibration willgenerate additional friction forces in the calibration platform and causeerroneous readings and hysteresis.9.13 Perform the calibration procedure of
46、 Section 9 for thesecond wheel transducer, if applicable.10. Report10.1 The calibration report shall contain the followinginformation:10.1.1 Skid measuring system identification,10.1.2 Wheel-transducer identification,10.1.3 Date,10.1.4 Test equipment identification in accordance withcalibration repo
47、rt(s),10.1.5 Test tires identification,10.1.6 Static weight at wheels and hitch,10.1.7 Setting of the skid tester variables,10.1.8 Measured values H (hitch height) and L (length fromhitch to wheel center).10.1.9 Tow vehicle standardization details,10.1.10 Instrumentation check-out details,10.1.11 Or
48、ientation of the transducer-sensitive axis,10.1.12 Statement of loading conditions under which thereadouts are zeroed,10.1.13 Loading conditions under which the reference cali-bration points are applicable,10.1.14 Record of the on-board and external indicatoroutputs of each transducer output versus
49、increasing and de-creasing traction force and vertical load (force),10.1.15 Statement of calibration values, linearity, and hys-teresis characteristics for the transducer and its associatedreadout,10.1.16 Correlation of external meter output with on-boardmeter or recorder output,10.1.17 Report section for a second transducer, if appli-cable, and10.1.18 Remainder of operating coefficients established inSection 9, ambient temperature range during the calibration,and notes on calibration procedures.11. Precision and Bias11.1 As a rule of thumb, instrumentatio
