1、Designation: B 539 02 (Reapproved 2008)Standard Test Methods forMeasuring Resistance of Electrical Connections (StaticContacts)1This standard is issued under the fixed designation B 539; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisi
2、on, 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 These test methods cover equipment and techniques formeasuring the resistance of static electrical co
3、nnections such aswire terminations or splices, friction connectors, solderedjoints, and wrapped-wire connections.1.2 Measurements under two distinct levels of electricalloading are described. These levels are: (1) dry circuit, (2) andrated current. One or both of these levels of loading may berequir
4、ed in specific cases.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to become familiarwith all hazards including those identified in the appropriateMaterial Safety Data Sheet (MSDS) for th
5、is product/materialas provided by the manufacturer, to establish appropriatesafety and health practices, and determine the applicability ofregulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2B 542 Terminology Relating to Electrical Contacts andTheir UseE 122 Practice for C
6、alculating Sample Size to Estimate,With Specified Precision, the Average for a Characteristicof a Lot or Process3. Terminology3.1 Definitions: See Terminology B 542 for definitions ofcontact resistance, film resistance, and constriction resistance.3.1.1 bulk resistance, nthe resistance a contact ass
7、emblywould have if it were solid metal of an identical geometry sothat the nominal contact area offered zero resistance. Whenmeasuring contact resistance one attempts to include as littlebulk resistance as possible in the measurement, by placingmeasuring probes as close to the contact interface as p
8、ractical.3.1.2 connection resistance, nthe resistance from thetermination point on one end of a device containing staticcontacts, through the contacts to the termination point on theother end of the device. The termination point is the location ona terminal of a device where a wire or printed circui
9、t pathelectrically connects to the terminal. This resistance is thevalue of resistance displayed by the device in a circuitapplication.3.1.2.1 DiscussionThe term contact resistance is oftenused in commercial literature to indicate the connection resis-tance displayed by the device in a standard appl
10、ication. In themore rigorous usage of contact resistance, the connectionresistance is the sum of the contact resistance plus the bulkresistance of leads within the device that go to the staticcontacts from the point that the leads are connected to theexternal circuitry. Measurement of contact resist
11、ance indepen-dent of all bulk resistance is very difficult for most commercialdevices.3.1.3 dry circuit, na circuit in which the open-circuitvoltage is less than or equal to 20 mV. Current is usually lowin a dry circuit, but a low-current circuit is not necessarily adry circuit. When the applied vol
12、tage (open-circuit voltage)istoo low to cause any physical changes in the contact junction,such as break-down of thin insulating films or softening ofcontact asperities, the circuit is said to be a dry circuit.3.1.4 open-circuit voltage, nthe steady-state voltagewhich would appear across the contact
13、s if they were opened.3.1.5 static contacts, nelectric junctions designed forinfrequent separation and connection, and intended to performtheir function only when contacting members are stationaryrelative to each other. This definition includes crimped,welded, brazed, riveted, or soldered joints; fr
14、iction connectionssuch as pin and socket connectors or taper pins, twisted-wiresplices; and connections made with screws, or bolts and nutsbetween electrical wiring and components. The definitionexcludes relay contacts, slip rings and commutators, andswitches and circuit breakers.3.2 Descriptions of
15、 Terms for Levels of Electrical Loading:1These test methods are under the jurisdiction of ASTM Committee B02 onNonferrous Metals and Alloys and are the direct responsibility of SubcommitteeB02.11 on Electrical Contact Test Methods.Current edition approved March 1, 2008. Published March 2008. Origina
16、llyapproved in 1970. Last previous edition approved in 2002 as B 539 02e1.2For 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
17、ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.1 dry circuit, nThis method provides for measurementof contact resistance under very low levels of electricalexcitation, with applied voltages and currents selected to
18、be toolow to cause breakdown of thin oxide films or other contami-nates in the contact interface or to cause formation of metallicbridges across the interface where none may otherwise exist.Dry circuit testing is intended to determine whether the testcontact will function properly in circuits of arb
19、itrarily lowlevels of electrical excitation. Dry circuit testing proceduresshould be used when the possibility of films or contaminants inthe contact interface exists or when the test sample is ulti-mately intended for use in a low-level circuit. This testing mustprecede other tests on the same samp
20、les at high levels ofelectrical loading.3.2.2 rated current, nThe rated current for a static contactdevice is determined or specified by the vendor or user of thedevice. The rated current may be large enough to causesignificant heating of the test samples. When rated currentmeasurements of contact r
21、esistance are required, using eitherac or dc test currents, the procedures outlined for temperaturestabilization in 9.5.3 must be followed.4. Summary of Test Methods4.1 The test methods described herein are characterized asfour-terminal resistance measuring techniques, wherein a mea-sured and contro
22、lled test current is introduced into the sampleusing two“ terminals” or connecting points, and two otherpoints are selected on the sample across which a voltage dropis measured. This voltage drop, divided by the test current, isthe effective overall resistance of the sample included betweenthe volta
23、ge probes. The voltage-measuring points are chosen soas to measure as closely as possible the voltage drop due onlyto the contact resistance of the sample and to eliminate fromthe measurement as much as possible the resistance of themetal pieces comprising the contact and the resistance of thewires
24、and connections used to introduce the test current into thesample.4.2 Two different levels of test current are specified. Thechoice of which level to use is governed by the application andrequirements of the electrical connection being tested. Elec-tronic signal-circuit connections may require low-l
25、evel (dry-circuit) testing, whereas power-handling wire connectorsshould be tested at rated current.4.3 Either ac or dc test currents may be used, with appro-priate instrumentation.5. Significance and Use5.1 As stated in Terminology B 542, contact resistance iscomprised of a constriction resistance
26、and a film resistance.When present, the latter of these is usually much greater invalue and dominates the contact resistance. For a given contactspot, when the film resistance is zero or negligible the contactresistance for that spot is nearly the same as the constrictionresistance and therefore, as
27、 a practical matter, has a minimumvalue which represents a clean metal-to-metal contact spot. Asreal contact surfaces exhibit varying degrees of roughness, realcontacts are necessarily composed of many contact spots whichare electrically parallel. In practical cases the clean metal-to-metal contact
28、spots will carry most of the current and the totalcontact resistance is primarily dependent on the size andnumber of metallic contact spots present (see Note 1). Inaddition, acceptably low values of contact resistance are oftenobtained with true areas of contact being significantly less thanthe appa
29、rent contact area. This is the result of having a largenumber of small contact spots spread out over a relatively largeapparent contact area.NOTE 1The term metallic contact as used here is intended to includethe so called quasi-metallic contact spots as well. The latter case wasdiscussed in Electric
30、 Contacts by Holm.35.2 The practical evaluation and comparison of electricalconnections depend in large part on their contact resistancecharacteristics. On the one hand, the absolute value of contactresistance is greatly dependent on the amount of metalliccontact established and indicates initially
31、how efficient thesystem is in producing areas of metallic contact. On the otherhand, a comparison of the initial resistance to the resistanceafter aging indicates how stable the system is in maintainingthe initial contact area. Both of these characteristics should beconsidered when evaluating contac
32、t systems. The criteriaemployed in evaluating contact resistance and stability are nota part of these test methods as they depend on specificapplications and therefore, will not be quantitatively stated.However, an estimate of contact resistance3resulting fromgood metallic contact can be made for a
33、given physicalsituation and used as a comparison to actual measurements todetermine how effective the system is in establishing stablemetallic contact. Resistances measured by these methodsbefore, during and after simulated life tests are used as a meansof determining the stability of contacts withi
34、n a device.6. Interferences6.1 Measurement of Low Resistance:6.1.1 Contact resistances are normally very small, rangingfrom microohms to a few milliohms in cases of practicalinterest. The measurement of resistance in this range requiresspecial techniques to eliminate effects of thermal potentials,ex
35、ternal interference, and resistance of connections and wiresleading to the test sample.6.1.2 The resistance-measuring procedures in these testmethods are four-terminal techniques. Test current in thesample is measured and controlled, and made independent ofthe sample resistance. Voltage-measuring pr
36、obes are attachedto the sample so as to eliminate the effects of connections of thesample into the test circuit. If the purpose of the measurementis to determine the contact resistance, the voltage measuringprobes are attached as close as feasible to the static contacts, soas to include as little of
37、 the bulk resistance of the sample aspossible in the measurement of the contact resistance.6.1.3 Two wire measurements of resistance are not suitablebecause connections to the sample will contribute part of themeasured resistance, and these may be large, unknown, andvariable.3Calculations and formul
38、ae for contact resistance of various types of contacts arecovered very thoroughly in Holms Electric Contacts, 4th Edition, Springer-Verlag,New York.B 539 02 (2008)26.1.4 Because the resistance being measured is often in themicroohm or milliohm range, and it is determined by measur-ing the potential
39、across the static contacts, the value of thepotential is often in the microvolt or millivolt range. As aresult, thermal potentials may be significant in relation to thepotential being measured and appropriate measures are re-quired to cancel or eliminate their effects.6.1.5 In the dry circuit method
40、, high potential may change aresistance by breaking down a film. Appropriate caution isrequired to obtain valid dry circuit resistance measurementsincluding limiting the open circuit voltage of the measuringapparatus that is connected to the device under test.6.2 ac Versus dc Measurements:6.2.1 Eith
41、er method described herein can be used with ac ordc test currents, with appropriate changes in instrumentation tocorrespond with the power supply. The methods are describedas using dc test currents, and the following comments applywhen ac is used.6.2.2 ac measurements should be expressed as RMS unle
42、ssotherwise defined in the test report. Take appropriate measuresto isolate the measurements from stray signals, especially sixtyhertz power line noise. Commercial resistance measuringinstruments that use ac test currents generally are suitableproviding that they meet other requirements of the stand
43、ard.7. Apparatus and Test Circuits7.1 Fig. 1 shows the basic arrangement of a four wire circuitfor measuring. In the illustration, the measured resistance is theresistance between the points where the voltmeter is attached tothe test specimen, that is, between the points of V1 and V2. Themeasured re
44、sistance includes the contact resistance at thecontact between the two rounded points and the bulk resistanceout to the point where the voltage probes touch the testspecimen. To measure connection resistance, move the voltageprobes away from the contact point to the very end of eachcontact member wh
45、ere the current leads are attached. Toattempt to measure contact resistance, move the voltage probesas close as possible to the contact point. The equipmentconsists of the following elements:7.1.1 Power SupplyA supply capable of providing therequired current and, in the case of the dry circuit measu
46、rementcapable of limiting the current to 100 milliamps and the opencircuit voltage to 20mV. The supply may be dc or ac, but thevoltage measuring device must match the type of current fromthe supply.7.1.2 Voltmeters and ammeters built into power suppliesmay or may not meet the requirements of these m
47、ethods withrespect to accuracy or precision. External metering should beused when necessary.7.1.3 Both output terminals of the dc supply must beisolated from the power line, the case of the supply, and thebuilding ground. This prevents “ground loops” or undesiredconnections through ground, between t
48、he power supply andother measuring instruments (such as an electronic voltmeter)attached to the sample.7.1.4 The maximum current required in the power supplycan be estimated from Table 1, which gives rated currents forvarious wire-size terminations according to Military specifica-tions.7.1.5 The out
49、put current of the power supply should bevariable and readily and accurately adjustable.7.2 Current Measuring Devicea meter, ac or dc, to matchthe power supply current type or suitable alternate measuringcircuitry is needed. The accuracy of the device must be 1 % orbetter of the measured current. Some power supplies includemeasurement capability of sufficient accuracy. An externalarrangement of a calibrated fixed resistor wired in series withthe test current and a voltmeter across the resistor is suitableprovided that it achieves the accuracy required.7.3 Reversing Switch
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