1、Designation: F 2537 06Standard Practice forCalibration of Linear Displacement Sensor Systems Used toMeasure Micromotion1This standard is issued under the fixed designation F 2537; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、 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 practice covers the procedures for calibration oflinear displacement sensors and their corresponding po
3、wersupply, signal conditioner, and data acquisition systems (lineardisplacement sensor systems) for use in measuring micromo-tion. It covers any sensor used to measure displacement thatgives an electrical voltage output that is linearly proportional todisplacement. This includes, but is not limited
4、to, linearvariable differential transformers (LVDTs) and differentialvariable reluctance transducers (DVRTs).1.2 This calibration procedure is used to determine therelationship between output of the linear displacement sensorsystem and displacement. This relationship is used to convertreadings from
5、the linear displacement sensor system intoengineering units.1.3 This calibration procedure is also used to determine theerror of the linear displacement sensor system over the range ofits use.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It
6、 is theresponsibility of 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. Terminology2.1 Definitions:2.1.1 calibrated range, ndistance over which the lineardisplacement sensor system is calibrat
7、ed.2.1.2 calibration certificate, ncertification that the sensormeets indicated specifications for its particular grade or modeland whose accuracy is traceable to the National Institute ofStandards and Technology or another international standard.2.1.3 core, ncentral rod that moves in and out of the
8、sensor.NOTE 1It is preferable that the sensors prevent the core from exitingthe sensor housing.2.1.4 data acquisition system, nsystem generally consist-ing of a terminal block, data acquisition card, and computerthat acquire electrical signals and allows them to be capturedby a computer.2.1.5 differ
9、ential variable reluctance transducer (DVRT),na linear displacement sensor made of a sensor housing anda core. The sensor housing contains a primary coil and asecondary coil. Core position is detected by measuring thecoils differential reluctance.2.1.6 linear displacement sensor, nan electrical sens
10、orthat converts linear displacement to electrical output.2.1.7 linear displacement sensor system, na system con-sisting of a linear displacement sensor, power supply, signalconditioner, and data acquisition system.2.1.8 linear variable differential transformer (LVDT), nalinear displacement sensor ma
11、de of a sensor housing and acore. The sensor housing contains a primary coil and twosecondary coils. When an ac excitation signal is applied to theprimary coil, voltages are induced in the secondary coils. Themagnetic core provides the magnetic flux path linking theprimary and secondary coils. Since
12、 the two voltages are ofopposite polarity, the secondary coils are connected in seriesopposing in the center, or null position. When the core isdisplaced from the null position, an electromagnetic imbalanceoccurs. This imbalance generates a differential ac outputvoltage across the secondary coils, w
13、hich is linearly propor-tional to the direction and magnitude of the displacement.When the core is moved from the null position, the inducedvoltage in the secondary coil, toward which the core is moved,increases while the induced voltage in the opposite secondarycoil decreases.2.1.9 null position, n
14、the core position within the sensorhousing where the sensor voltage output is zero (some sensorsdo not have a null position).2.1.10 offset correction, nremoval of any offset in asensors output so that at zero displacement, zero voltage isrecorded.1This practice is under the jurisdiction ofASTM Commi
15、ttee F04 on Medical andSurgical Materials and Devices and is the direct responsibility of SubcommitteeF04.15 on Material Test Methods.Current edition approved Dec. 1, 2006. Published December 2006.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, Un
16、ited States.2.1.11 percent error, nthe difference between a measure-ment of a reference standard and the actual length of thereference standard divided by the actual length of the referencestandard and the result converted to a percent.2.1.12 power supply, na regulated voltage source withoutput equa
17、l to that required by the sensor for proper operation.2.1.13 sensor housing, ncentral hole in a linear displace-ment sensor that senses movement of the core within it.2.1.14 signal conditioner, nelectronic equipment that actsto convert the raw electrical output from the linear displace-ment sensor i
18、nto a more useful signal by amplification andfiltering.3. Summary of Practice3.1 A linear displacement sensor is mounted in a calibrationfixture such that it can be subjected to a precise, knowndisplacement.3.2 Displacement is applied in steps over the full range ofthe linear displacement sensor and
19、 electrical readings (forexample, voltages) are collected using the linear displacementsensor system.3.3 Each voltage reading is taken as the average of 100readings over 0.1 s, decreasing the error of the reading. Theerror in the readings is recorded as the standard deviation in thereadings. This er
20、ror should be constant and independent ofdisplacement. It should be noted that the error in the readingsis a summation of errors in each of the linear displacementsensor system components.3.4 The calibration factor (S) is calculated as the slope ofthe voltage versus displacement curve using linear r
21、egression.3.5 Linearity of the sensor is assessed.3.6 The percent error is determined for each calibrationpoint collected. This percent error is evaluated together withthe tolerance of the micrometer head calibration.4. Significance and Use4.1 Linear displacement sensor systems play an importantrole
22、 in orthopedic applications to measure micromotion duringsimulated use of joint prostheses.4.2 Linear displacement sensor systems must be calibratedfor use in the laboratory to ensure reliable conversions of thesystems electrical output to engineering units.4.3 Linear displacement sensor systems sho
23、uld be calibratedbefore initial use, at least annually thereafter, after any changein the electronic configuration that employs the sensor, afterany significant change in test conditions using the sensor thatdiffer from conditions during the last calibration, and after anyphysical action on the sens
24、or that might affect its response.4.4 Verification of sensor performance in accordance withcalibration should be performed on a per use basis both beforeand after testing. Such verification can be done with a lessaccurate standard than that used for calibration, and may bedone with only a few points
25、.4.5 Linear displacement sensor systems generally have aworking range within which voltage output is linearly propor-tional to displacement of the sensor. This procedure is appli-cable to the linear range of the sensor. Recommended practiceis to use the linear displacement sensor system only within
26、itslinear working range.5. Apparatus and Equipment5.1 Linear Displacement Sensor.5.2 Power Supply, with output equal to that required by thesensor.5.3 Signal Conditioner, Data Acquisition System, and Re-lated Cables and Fittings.5.4 Test MethodMicrometer Fixture Calibration:5.4.1 Calibration Fixture
27、, a fixture that provides a means forfixing both a micrometer head and the linear displacementsensor along a parallel displacement axis, and is capable ofapplying displacement to the linear displacement sensorthroughout its linear range. The alignment tolerance of thecalibration fixture must be meas
28、ured.5.4.2 Micrometer Head, a precision instrument with knownerror (that is, tolerance). The spindle of the micrometer must benon-rotating and spring-loaded. The micrometer head shall becalibrated annually by the manufacturer or other qualifiedpersonnel.6. Hazards6.1 Safety Hazards:6.1.1 This practi
29、ce involves electrical equipment. Verifythat all electrical wiring is connected properly and that thepower supply and signal conditioner are grounded properly toprevent electrical shock to the operator. Take necessary pre-cautions to avoid exposure to power signals.6.2 Safety Precautions:6.2.1 Exami
30、ne the sensor housing for burrs or sharp edges,or both. Remove any protrusions that might cause harm.6.2.2 The sensor can be permanently damaged if incorrectlyhandled. Consult the manufacturers guidelines for handling.6.2.3 The sensor can be permanently damaged if incorrectlyconnected to the power s
31、upply, or if connected to a powersupply with the wrong excitation level. Consult the manufac-turers guidelines for use.6.2.4 Follow all manufacturers recommendations with re-gard to safety.6.3 Technical Precautions:6.3.1 If using a linear displacement sensor that permits thecore to leave the sensor
32、housing, do not interchange cores withother linear displacement sensor housings.6.3.2 Replace the sensor if it, or any component of it, showsany signs of dents, bending, or other defects that may affect itsperformance.6.3.3 Store all system components in dry, protective loca-tions when not in use.6.
33、3.4 Do not exceed the allowable input voltage of thesensor as specified by the manufacturer.6.3.5 Do not connect a voltage source to the output leads ofthe sensor.6.3.6 Do not over-tighten the sensor within the calibrationfixture.6.3.7 The behavior of some sensors may be affected bymetallic holders;
34、 this must be considered during use of thesensor.F25370627. Calibration and Standardization7.1 Verify that the calibration fixture, micrometer, powersupply, signal conditioner, and data acquisition system are allin good working order, and of sufficient precision and bias.7.2 Verify that all componen
35、ts have been individually cali-brated and are within their respective calibration cycles.8. Procedure8.1 Perform the calibration in an environment as close tothat in which the sensor will be used as possible. All necessaryequipment should be in the environment in which they are to beused for calibra
36、tion for at least 1 h prior to calibration tostabilize temperature effects. Ambient temperature should bequantified and recorded. Ambient temperature during thecalibration procedure should be maintained within 62C of theinitial temperature.8.2 Verify that the power supply is adjusted to supply there
37、commended voltage to the sensor.8.3 With equipment turned off, connect all power supply,signal conditioning, and data acquisition equipment exactly asit will be used in service. Follow the manufacturers suggestedorder of connecting equipment, if prescribed. Allow all elec-tronics to warm up for at l
38、east 15 min before beginningcalibration.8.4 Verify that the sensor is working properly by changingits displacement position and watching the signal changeaccordingly on the chart.8.5 Note the model number and serial number of the lineardisplacement sensor to be calibrated.8.6 Note the calibration pr
39、otocol to be followed.8.7 Confirm that the micrometer head, data acquisitionsystem, linear displacement sensor, and signal conditioner havebeen calibrated and are within their calibration cycles.8.8 If any calibration is not up to date, have the propercalibration performed before calibrating the sen
40、sor within thecurrent system.8.9 Note the tolerance of the micrometer head calibration.8.10 Record the name of the calibrator, date of calibration,all equipment used (model and serial numbers, if possible),calibration units, input voltage supplied, and input limits andresolution of the data acquisit
41、ion system.8.11 Test MethodMicrometer Fixture Calibration:8.11.1 Secure the sensor into the mounting fixture.8.11.2 Secure the mounting fixture into the calibrationfixture.8.11.3 Secure the micrometer head into the calibrationfixture.8.11.4 Define the zero position of the sensor. This is theposition
42、 of the first calibration point and it is located at one endof the linear range of motion of the sensor. This position isfound by positioning the sensor at its null position (where thevoltage output of the sensor is zero) and then rotating themicrometer head in one direction until the sensor has tra
43、veledto the end of its rated linear range in that direction (that is, adistance of12 of its total rated linear range).8.11.5 Record the sensor system readout as Sensor Reading1 in a table corresponding to zero displacement. Also includethe error in the position reading (that is, the tolerance of the
44、micrometer head and the combined largest error associatedwith the quantified misalignment of sensor and micrometerhead).8.11.6 Sample the voltage data from the sensor at a fastsampling rate for a finite time. (See Note 2.) Record theaverage and standard deviation of the sample in the table. It isrec
45、ommended that a software program be written or used toefficiently perform these tasks.NOTE 2At least 1000 Hz for 0.1 s is recommended.8.11.7 Move the micrometer to a predetermined displace-ment from the zero position. Move the micrometer in only onedirection, as there may be significant backlash in
46、the microme-ter that will result in unquantified errors in displacementmeasurements.8.11.8 Repeat steps 8.11.5 and 8.11.6 for the new position.8.11.9 Repeat steps 8.11.7 and 8.11.8 for uniform intervalsthroughout the linear range of the sensor.At least 10 calibrationpoints should be included.8.11.10
47、 Rotate the micrometer head in reverse order andrecord readings in the table throughout the linear range of thesensor.8.11.11 To obtain reproducibility data, repeat these steps fora minimum of two times using the same calibration positions.8.11.12 Calculate the calibration factor, linearity, errorbo
48、unds of each data point, displacement error, and percenterror as described in Section 9.9. Calculations9.1 Calibration FactorThe calibration factor (S) is calcu-lated as the slope of the voltage versus displacement curveusing linear regression.9.2 LinearityLinearity of the sensor can be assessed byc
49、alculating the coefficient of determination (R2) of a line fitthrough the data points using linear regression.9.3 Percent ErrorThe percent error is calculated for eachpoint collected. First, the difference between the displacementvalue of the point calculated from the calibration equation andthe actual measurement of the displacement at the pointcollected is calculated. The percent error of each point is 1003the resulting difference/the calibrated range.10. Acceptability Criteria10.1 In order for the sensor to be used, it must be calibratedwithin the followin
