1、Standard Method of Test for Calibrating a Wheel Force or Torque Transducer Using a Calibration Platform (User Level) AASHTO Designation: T 282-01 (2015)1ASTM Designation: E556-95(2000) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washing
2、ton, D.C. 20001 TS-5a T 282-1 AASHTO Standard Method of Test for Calibrating a Wheel Force or Torque Transducer Using a Calibration Platform (User Level) AASHTO Designation: T 282-01 (2015)1ASTM Designation: E556-95(2000) 1. SCOPE 1.1. This method covers the calibration of the force (or torque) tran
3、sducer and associated instrumentation of a mounted test wheel by using a calibration platform. It is used for establishing correction factors for changes in transducer output due to changes in operating conditions. 1.2. This method is a static calibration, simulating the traction force between a tir
4、e and the pavement. 1.3. In the case of a force-measuring system, the instrumentation readout is directly proportional to the calibration force input. 1.4. In the case of a torque-measuring system, the instrumentation readout is a measure of the calibration force input and the effective tire radius.
5、 1.5. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of whoever uses this standard to consult and establish appropriate safety and health practices and de
6、termine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standard: T 242, Frictional Properties of Paved Surfaces Using a Full-Scale Tire 2.2. ASTM Standard: F377, Standard Practice for Calibration of Braking/Tractive Measuring Devices for Testing Tires 3
7、. TERMINOLOGY 3.1. Description of Terms Specific to This Standard: 3.1.1. wheel force transducer systema force-to-electrical signal converter system including transducer(s), associated signal condition, zeroing, amplifying, recording, and monitoring instrumentation. 2016 by the American Association
8、of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-5a T 282-2 AASHTO 3.1.2. calibration reference signalsrepeatable signals in the range of expected wheel-force transducer system loading. These signals could be either constant voltages
9、 (preferably) or produced by a strain-gauge calibration shunt resistor. 3.1.3. calibration platforma moving platform for applying a force in the contact plane of a tire, and associated means for measuring the applied force. The calibration platform consists of a rigid plate with a high-friction surf
10、ace, in contact with the tire footprint, supported on a frictionless, preferably air, bearing. It may also be instrumented to measure vertical forces (loads). 3.1.4. hysteresisthe maximum difference between corresponding transducer outputs (of the wheel force transducer system) at increasing and dec
11、reasing applied calibration force, expressed as a percentage of full load. Proven outliers are excluded. 3.1.5. linearity/nonlinearitythe maximum deviation of the transducer output(s) (of the wheel force transducer system) from the “best-fit” linear relation to the applied calibration force, express
12、ed as a percentage of full scale. Proven outliers are excluded. 3.1.6. test wheela wheel and test tire assembly mounted to a test vehicle by means of a force or torque transducer. 3.1.7. crosstalkthe undesired effect of force readings appearing on an unloaded axis of a transducer while applying forc
13、e to another. 3.1.8. horizontal traction (traction)a force acting in a horizontal axis through the wheel transducer, i.e., locked wheel drag force. 3.1.9. vertical load (load)force acting in a vertical axis through the wheel transducer, i.e., weight. 4. SUMMARY OF METHOD 4.1. The vertical static loa
14、ds (forces) on the test wheel(s) and hitch are established. If the tester is of the trailer type, it must be connected to its tow vehicle. Traction forces are applied to the locked wheel(s) at the tireplatform interface. The wheel transducer is calibrated while trailer and tow vehicle displacements
15、are measured from the initial position for the applied traction force. The calibration platform consists of a bearing that is frictionless in all directions of the horizontal plane supporting a rigid plate with a high-friction surface. The force applied to this platform is measured by a suitable tra
16、nsducer. 4.2. Wheel transducer linearity and hysteresis are determined by recording data using an electronic digital meter and/or an x-y plotter, and should also be correlated with data collected from the tow vehicle instrumentation. Techniques are given for establishing reference signals to be used
17、 as calibration points. 4.3. With calibration platforms having force-measurement capability also in the vertical direction, test-wheel load (force) is recorded as a function of the applied tractive calibration force. 4.4. With a wheel transducer also having normal load (force)-measuring capability,
18、the transducer output is compared with the corresponding vertical output of the calibration platform. 5. SIGNIFICANCE AND USE 5.1. Wheel force or torque transducers are used under dynamic test conditions, and the measurements are subject to many error sources. The static calibration recommended by t
19、he present standard 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-5a T 282-3 AASHTO cannot eliminate all error sources. Its significance is in providing an accurate calibration of the transducer an
20、d the associated electronics, readout, and recording equipment. 5.2. The calibration result may be used to make either mechanical or electronic adjustments until the readout agrees with the calibration input. Alternatively, calibration curves or tables may be prepared to be used as corrections to me
21、asured results. 6. APPARATUS 6.1. The calibration apparatus shall consist of the basic components described below, and calibrated in accordance with Section 6.3 of ASTM F377. 6.1.1. A calibration platform for applying tractive forces at the tireplatform interface of a test wheel, with a calibrated i
22、nternal or external reference force transducer to measure these forces. Capability of measuring vertical forces (wheel loads) also is desirable. 6.1.2. A system for generating traction forces applied through the calibration platform. 6.1.3. Instrumentation for recording or indicating transducer outp
23、uts, including digital meters and, optionally, an x-y recorder. 6.1.4. An accurate level, tire pressure gauge, and thermometer for measuring ambient temperatures. 6.1.5. Scale(s) for measuring vertical wheel load, accurate within 0.5 percent of maximum expected axle load for the test trailer. 7. PRE
24、PARATION OF APPARATUS 7.1. SiteSelect a sheltered, level, paved area. (A hard surface, preferably under cover, is desirable.) 7.2. Calibration Platform and Associated InstrumentationPrepare the calibration platform and associated instrumentation following established setup procedures and the manufac
25、turers manuals where applicable. 7.3. Test TiresSet the inflation pressure under normal vertical load (force). Inflation pressure shall be 165.0 3.5kPa (24.0. 0.5 psi) at ambient temperature (cold). 7.4. Traction Tester InstrumentationCheck the test vehicle instrumentation by following established s
26、etup procedures for the system with reference to the recommended procedure in the manufacturers manual, where applicable. Set all gains and offsets at values normally used during friction testing. Record the settings. 7.4.1. Force-Type TransducerLoad crosstalk into traction; if, with full normal loa
27、d back on the test wheel, the traction output is different from zero by more than 1 percent of the applied normal load, adjust by either rotating the transducer (if provisions for rotation have been made) or by changing the hitch height; that is, tilting the trailer to orient the transducer horizont
28、al axis parallel to the calibration plane. Then apply 2.2 kN (500 lbf) of traction force and note the change in load reading. If more than 1 percent crosstalk, check transducer leveling and repeat this test. 7.4.2. Torque-Type TransducerUse steps in Sections 7.4 and 7.4.1, substituting the torque ou
29、tput for the traction. If the load into torque crosstalk is greater than 1 percent of the applied normal load, refer to the manufacturer since there are normally no user adjustments. 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a
30、 violation of applicable law.TS-5a T 282-4 AASHTO 7.5. Test TrailerPosition the trailer coupled to its tow vehicle on level ground and set the trailer variables such as tire pressure, hitch height, and inflation pressure of air shock absorbers, where present, to the normal operating values. Measure
31、the hitch height from level ground to the center of the hitch. Decouple the trailer and weigh it at each point of support, maintaining its relative level. Correct the weights, if needed, to comply with T 242. Recouple the trailer to the towing vehicle. Note 1The tow vehicle should have one-half tank
32、 of water and a full fuel load before leveling the trailer. 7.6. Wheel TransducerWith the test wheel loaded, the wheel transducer traction output should be adjusted to zero. Then remove 2.2 kN (500 lbf) of the load and recheck traction zero. 7.7. Record all measures, weights, and dimensions, and the
33、 trailer-leveling adjustments that give zero transducer outputs. 8. PROCEDURE 8.1. Determine that the calibration platform has been suitably calibrated within a reasonable period of time (see Section 6.1). 8.2. If the test vehicle is of the trailer type, it should be hitched and aligned with the tow
34、 vehicle. The calibration may be performed with auxiliary electrical power for the instrumentation. In this case, after completing the calibration, check the system when powered by the vehicle electrical system with the engine running, to assure that the output(s) have not changed. The preparations
35、described in Section 7 shall have been performed. 8.3. Place the test wheel(s) on the calibration platform(s) using blocks, if needed, under the other wheels to maintain a level plane of support for all system tires. 8.4. With the test wheel raised clear of the platform, zero the output(s) of the ca
36、libration platform in accordance with established operating procedures. Zero the wheel transducer output(s). Note 2Warning: Make sure that the wheel brakes do not drag. 8.5. Align the calibration platform(s) and the associated force application system(s) with the test tire(s) and lower the test whee
37、l onto the platform. 8.6. The platform shall be level within 0.25 degree prior to calibration. Note 3Increased accuracy may be obtained by maintaining the aforementioned level throughout the calibration procedure. 8.7. Record the ambient temperature. To meet this standard, calibration can be done on
38、ly when the ambient temperature is between 4 and 38C (40 and 100F). 8.8. Use digital meter(s) and, optionally, x-y recorder(s) to observe the wheel force transducer system signals at the input to the system recorder. 8.8.1. With the trailer level and with full vertical load and zero traction force a
39、pplied to the test wheel(s), adjust the system vertical load indicator to correspond with the platform vertical load value. 8.8.2. Lock the test wheel and apply a midrange tractive force (typically 2.2 kN (500 lbf) via the platform to the test wheel. Adjust the system traction indicator to correspon
40、d with the platform traction value. Return the traction force to zero. 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-5a T 282-5 AASHTO 8.9. Record the wheel-transducer vertical load output and the
41、force-plate transducer vertical output, on both the system recorder and the meter, while increasing and decreasing the vertical force applied by at least 20 percent of the static wheel load value in 445-N (100-lbf) increments. This can be done by adding 90-kg (200-lb) shot bags; e.g., to the trailer
42、 wheel load. 8.10. Establish the linearity and hysteresis characteristics for the vertical transducer output, if applicable, using data in Section 8.9. 8.11. Record the wheel transducer output(s). (Horizontal traction and vertical load readings on both the system recorder and the meter while increas
43、ing and decreasing the traction force by 445-N (100-lbf) increments through the full calibration range (typically 0 to 50 percent of vertical load). Note 4For a two-wheeled towed test trailer, the test wheel vertical load should decrease linearly from the zero traction value as the applied traction
44、force increases at a slope proportional to the H/L ratio of the trailer, where H is the initial hitch height and L is the initial hitch-to-axle length (see T 242). The nontest wheel load (force) should remain constant at the zero traction value. 8.12. If the test wheel load and traction values obtai
45、ned in Sections 8.9 and 8.11 agree with the platform values within 1 percent, apply system load and traction calibration signals and record for future reference. If differences greater than 1 percent are found, the system may require maintenance or the crosstalk should be rechecked as described in S
46、ection 7.4. Note 5Some calibration platforms use ball or roller bearings (instead of air bearings). Any side force on the wheel under calibration will generate additional friction forces in the calibration platform and cause erroneous readings and hysteresis. 8.13. Perform the calibration procedure
47、of Section 8 for the second wheel transducer, if applicable. 9. REPORT 9.1. The report shall contain the following information: 9.1.1. Skid measuring system identification; 9.1.2. Wheel-transducer identification; 9.1.3. Date; 9.1.4. Test equipment identification in accordance with calibration report
48、(s); 9.1.5. Test tires identification; 9.1.6. Static weight at wheels and hitch; 9.1.7. Setting of the skid tester variables; 9.1.8. Measured values H (hitch height), L (length from hitch to wheel center), and T (track width); 9.1.9. Tow-vehicle standardization details; 9.1.10. Instrumentation check
49、out details; 9.1.11. Orientation of the transducer-sensitive axis; 9.1.12. Statement of loading conditions under which the readouts are zeroed; 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-5a T 282-6 AASHTO 9.1.13. Loading conditions under which the reference calibration points are applicable; 9.1.14. Record of the on-board and external indicator outputs of each transducer output versus increasing and decreasing traction force and vertical lo
