ASTM E1237-1993(2003) Standard Guide for Installing Bonded Resistance Strain Gages《安装耦合电阻应变仪》.pdf

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1、Designation: E 1237 93 (Reapproved 2003)Standard Guide forInstalling Bonded Resistance Strain Gages1This standard is issued under the fixed designation E 1237; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi

2、on. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This document provides guidelines for installin

3、g bondedresistance strain gages. It is not intended to be used for bulk ordiffused semiconductor gages. This document pertains only toadhesively bonded strain gages.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of th

4、e 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:E 251 Test Methods for Performance Characteristics ofMetallic Bonded Resistance Strain Gages22.2 Other Stand

5、ards:ANSI/SEM 1-1984; Standard for Portable Strain-IndicatingInstrumentsDesignation of Strain Gage Bridge andColor Code of Terminal Connections; August 16, 1984.33. Terminology3.1 Definitions:3.1.1 lead wirean electrical conductor used to connect asensor to its instrumentation.3.1.2 resistance strai

6、n gage bridgea commonWheatsone bridge made up of strain gages used for themeasurement of small changes of resistance produced by astrain gage, where the gages may be wired in the followingconfiguration (see also Fig. 1 and Fig. 2):Arm 1 between + excitation and signalArm 2 between excitation and sig

7、nalArm 3 between + signal and excitationArm 4 between + signal and + excitation3.2 Definitions of Terms Specific to This Standard:3.2.1 bonded resistance strain gagea resistive elementwith a carrier that is attached by bonding to the base materialso that the resistance of the element will vary as th

8、e surface ofthe base material to which it is attached is deformed. (For acomplete definition of this term see Test Methods E 251.)4. Significance and Use4.1 Methods and procedures used in installing bondedresistance strain gages can have significant effects upon theperformance of those sensors. Opti

9、mum and reproducibledetection of surface deformation requires appropriate andconsistent surface preparation, mounting procedures, and veri-fication techniques.5. Gage Selection5.1 Careful consideration must be given to the intended usewhen selecting an appropriate gage. Installation and operatingcha

10、racteristics of a gage are affected by many factors such asresistive element alloy, carrier material, gage length, gage and1This guide is under the jurisdiction of ASTM Committee E28 on MechanicalTesting and is the direct responsibility of Subcommittee E28.01 on Calibration ofMechanical Testing Mach

11、ines and Apparatus.Current edition approved June 10, 2003. Published January 2004. Originallyapproved in 1993. Last previous edition approved in 1998 as E123793(1998).2Annual Book of ASTM Standards, Vol 03.01.3Available from American National Standards Institute, 11 W. 42nd St., 13thfloor, New York,

12、 NY 10036.FIG. 1 Designation of Strain Gage Bridge and Color Code of LeadWires (Full Bridge)FIG. 2 Designations of Strain Gage Bridge and Color Code ofLead Wires (14 Bridge)1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.resistive el

13、ement pattern, solder tab type and configuration,temperature compensation characteristics, resistance of activeelements, gage factor, and options desired.5.2 Factors that should also be considered include type oftest or application, operating temperature range, environmentalconditions, accuracy requ

14、irements, stability, maximum elonga-tion, test conditions (static or dynamic) and duration, andsimplicity and ease of installation. Dissipation of self-generated heat to the carrier should be considered in selectinggage resistance and size of grid.5.3 To minimize errors due to strain gradients over

15、the gagearea, gage size should normally be small with respect to thedimensions of an immediately adjacent geometric irregularity(hole, fillet, etc.). However, the gage size should generally belarge relative to the underlying material structure (grain size,fabric-reinforced composite weave pattern, e

16、tc.).5.4 A two- or three-element rosette gage should be usedunless the strain state is unquestionably uniaxial. A singleelement gage may be selected to measure the strain due to auniaxial strain state if the principal directions are known.5.5 Temperature compensation of the gage should be se-lected

17、to match the thermal coefficient of expansion of the basematerial, where possible. As a note of caution, for extremetemperature changes, nominal or handbook data on the thermalexpansion characteristics of the base material may not besufficiently accurate, and actual calibration may be required.5.6 S

18、train gage manufacturers provide detailed critiques ofthe various factors which affect gage selection (1).45.7 For nonroutine applications, the advice of experiencedusers and of strain gage manufacturers should be sought.Specific verification tests may be required to ensure accurateresults.6. Bondin

19、g Technique Selection6.1 Selection of the proper bonding technique and agent isimportant. Because the bonding agent becomes part of thestrain gage system, many of the gage selection factors shouldbe considered in bonding technique or agent selection.6.2 Additional selection factors include compatibi

20、lity of thebonding materials used in the selected gage construction withthe material under test, environmental conditions, and availableinstallation time.6.3 Strain gages from different manufacturers may differ.Generally, each manufacturer will supply instructions andrecommendations for bonding. The

21、se instructions should beconsidered when making a selection.7. Surface Preparation7.1 The surface must be properly prepared to ensure goodbonding. Surface preparation includes solvent degreasing,cleaning, mechanical preparation, and chemical preparation.The surface should be smooth, but not highly p

22、olished.Preparation of this surface must be compatible with the gage,bonding method, and base material.7.2 Erroneous gage readings may be caused by poor bond-ing of strain gages, which could be due to unremoved coatingssuch as paint, scale, rust, and oils. Poor bonding may also resultfrom applying g

23、ages to improperly prepared surfaces, such asmirror smooth finishes or surfaces containing deep pits andgouges.7.3 Strain gage manufacturers supply surface preparationsuggestions and recommendations. This information should bereviewed and considered when preparing base material sur-faces for the par

24、ticular gages selected.8. Gage InstallationGeneral8.1 All work must be performed with clean hands and tools.All materials needed should be assembled and readily availableat the gage installation location.8.2 The specific surface preparation procedures should be inaccordance with the instructions sup

25、plied for the bonding agentselected. Bonding agent handling and safety precautionsshould be reviewed and carefully followed.8.3 The detailed gage installation procedures available fromthe strain gage manufacturer for the particular gage/bondingtechnique system selected should be carefully reviewed a

26、ndrigorously followed. Deviations from these procedures, if any,should be documented and verified to ensure that the installa-tion will yield suitably accurate results.8.4 Gage handling and alignment procedures should berigorously followed. Deviations, if any, should be documented.9. Gage Installati

27、onAdhesive9.1 Ensure that the proper adhesive is selected for a givengage type. Follow gage manufacturers recommendations forselecting an adhesive.9.2 The environment to which a gage is to be subjected andtest duration should be considered when selecting an adhesive.9.3 Ensure that the adhesive to b

28、e used is not out-of-datewith regard to storage and shelf life requirements.9.4 Ensure that test material temperature range and gage/bonding system temperature range are compatible.9.5 Temperatures and times should be monitored to ensurethat the adhesive temperature and pot life requirements, ifappl

29、icable, are not exceeded.9.6 Adhesive curing methods and schedules should berigorously followed. Deviations, if any, should be documented.9.7 If curing with pressure is required, take special care tomake sure the pressure is proper and is distributed uniformlyover the entire gage. Nonuniform pressur

30、e may result in anirregular bond line. Care should be taken to ensure that thegage position does not shift as a result of applying thispressure.10. Lead Wire Connection10.1 Care must be exercised in attaching the lead wires. Inorder to prevent lead wire forces from damaging the strain gageor degradi

31、ng its performance, the use of gages with integralcopper terminals or bonded terminals is recommended. Bond-able terminals are recommended where extended use of the testpiece is expected. References (2), (3), and (4) provide supple-mental information on these subjects.4The boldface numbers in parent

32、heses refer to the list of references at the end ofthis standard.E 1237 93 (2003)210.2 Wire splices should be avoided, but if a splice isrequired, ensure a good electrical and mechanical connection.The preferred method includes crimping, soldering, and insu-lating.10.3 It is important to select the

33、proper wire type, size, andlength to maintain strain gage stability, sensitivity, and integ-rity. Moisture can cause signal instability and drift, hence thelead wire insulation integrity should be checked before instal-lation.10.4 The lead wires shall be identifiable by color or otheridentifying mar

34、k. Unless specified otherwise, gages shall bewired into a strain gage bridge configuration that conforms tothe ANSI/SEM 1-1984.10.4.1 The following sign conventions should be used:tension, elongation, increased pressure, or other generallyaccepted positive quantities shall produce positive outputsig

35、nals.10.4.2 The color code for strain gage bridge wiring andconnections shall be as follows:Red + excitationGreen + signalBlack excitationWhite signal10.4.3 If all elements of the bridge are active, bridgeelements shall be arranged so that functions producing positiveoutput will cause increasing res

36、istance in arm 1, or 3, or both,and decreasing resistance in arm 2, or 4, or both, of the bridge.10.4.4 When only one bridge element is active (quarterbridge), arm 1 shall be used. (Arms 2, 3, and 4 shall be used asinactive elements.)10.4.4.1 For quarter-bridge applications, the installationshould u

37、sually consist of the 3-wire configuration with 3 leadwires between the gage and bridge.10.4.5 When two bridge elements are active and of oppositepolarity (half bridge), arms 1 and 2 shall be used. (Arms 3 and4 shall be used as inactive elements.) When two bridgeelements are active and of the same p

38、olarity, arms 1 and 3 shallbe used. (Arms 2 and 4 shall be used as inactive elements.)10.4.6 Soldering techniques are usually the same as thoseused for most electronic soldering applications, although somestrain gage installations require more sophisticated techniques.Noncorrosive fluxes and minimum

39、 heats shall be employed.10.4.7 Residual flux shall be removed with a suitable brushor cotton swab and cleaning solvent. If open faced, protect gridwhile soldering and cleaning.11. Verification Checks11.1 The completed strain gage installation shall be checkedprior to use to verify its integrity and

40、 ability to provide reliableand repeatable data.11.2 Initial Checks After Installation:11.2.1 Visually check the bonded strain gage after installa-tion, after the cement has cured, and before the lead wire issoldered. The gage should be examined visually for thefollowing:11.2.1.1 Gage is accurately

41、located and oriented with re-spect to pre-marked reference lines.11.2.1.2 A small amount of excess adhesive is visiblecompletely around the gage periphery.11.2.1.3 There is complete adhesion at the gage edges andcorners. Gage should appear to be flat on the surface.11.2.1.4 There is no evidence of a

42、ir bubbles or mottled gageappearance.11.2.2 Check gage resistance. Shifts greater than 0.5 % areindicative of damage due to improper handling or clampingwhen using adhesives with room temperature cure. Installa-tions using elevated temperature cure may exhibit higher shiftsbut in no case should they

43、 exceed 2 % and then similarinstallations should exhibit uniformity of the shift to within0.5 %.11.2.3 Check resistance between grid of a bonded straingage and the surface to which the gage is attached.Aresistanceof at least 1000 MV is desirable, and 10 000 MV is normal.However, a minimum reading of

44、 20 MV is necessary foraccurate, stable functioning of the gage.NOTE 1When testing for high resistances between the grid/strainelement and ground, a conventional low-voltage ohmmeter should beused. High-voltage insulation testers can damage the gage.11.3 Checks After Lead Wire Connections:11.3.1 Aft

45、er the lead wire has been soldered to the bondedstrain gage terminals, and terminals have been properlycleaned, visually examine the connections. They should be:11.3.1.1 Smooth, no solder spikes,11.3.1.2 Shiny; frosty appearing surfaces should be resol-dered, and11.3.1.3 Free of discoloration from f

46、lux residues.11.3.2 Verify the electrical continuity by measuring thecombined gage and lead wire resistance. This will validate thesolder connection, the lead wire, and the splices in the leadwire. If this shows an open circuit or indicates a resistancedifferent from that measured in 12.2.3 plus the

47、 resistance of thelead wire, the gage could have been damaged during the leadwire installation, a bad solder joint or a bad splice or both wasmade. The cause of the observed resistance difference shouldbe determined and corrective action taken.11.3.3 Quickly check on the gage bond (5).11.3.3.1 Conne

48、ct the gage to a static strain indicator, datasystem, or other readout device.11.3.3.2 Balance the bridge.11.3.3.3 Press lightly on the strain gage grid area with theeraser end of a lead pencil.11.3.3.4 When pressure is applied the strain indicator shouldshow some movement; and, when removed, the in

49、dicatorshould return to zero.11.3.3.5 If the indicator fails to return to zero or looksunstable, then the gage is probably either poorly bonded (forexample air bubbles, delaminations, etc.) or damaged and willhave to be replaced.NOTE 2This test should not be performed on an open-face gage(exposed grid) without interposing a layer of mylar, TFE fluorocarbon,etc.12. Protective Coatings12.1 False or erratic strain indications can result from theeffects of moisture, chemical attack, mechanical damage, orE 1237 93 (2003)3other variables. After verification of response