1、Designation: B 539 02e1Standard 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 revision, the year of
2、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.e1NOTEEditorial changes were made throughout in April 2003.1. Scope1.1 These test methods cover equipment and techniques formeasu
3、ring the resistance of static electrical connections 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 b
4、oth of these levels of loading may berequired 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 appropri
5、ateMaterial Safety Data Sheet for this product/material as pro-vided by the manufacturer, to establish appropriate safety andhealth practices, and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:B 542 Terminology Relating to Electrical Cont
6、acts andTheir Use2E 122 Practice for Calculating Sample Size to Estimate,With a Specified Tolerable Error, the Average for aCharacteristic of a Lot or Process33. Terminology3.1 Definitions: see Terminology B 542 for definitions ofcontact resistance, film resistance, and constriction resistance.3.1.1
7、 bulk resistancethe resistance a contact assemblywould 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 p
8、robes as close to the contact interface as practical.3.1.2 connection resistancethe resistance from the termi-nation point on one end of a device containing static contacts,through the contacts to the termination point on the other endof the device. The termination point is the location on aterminal
9、 of a device where a wire or printed circuit 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
10、 displayed by the device in a standard application. 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 theextern
11、al circuitry. Measurement of contact resistance indepen-dent of all bulk resistance is very difficult for most commercialdevices.3.1.3 dry circuita circuit in which the open-circuit voltageis less than or equal to 20 mV. Current is usually low in a drycircuit, but a low-current circuit is not necess
12、arily a dry circuit.When the applied voltage (open-circuit voltage) is too low tocause any physical changes in the contact junction, such asbreak-down of thin insulating films or softening of contactasperities, the circuit is said to be a dry circuit.3.1.4 open-circuit voltagethe steady-state voltag
13、e whichwould appear across the contacts if they were opened.3.1.5 static contactselectric junctions designed for infre-quent separation and connection, and intended to perform theirfunction only when contacting members are stationary relativeto each other. This definition includes crimped, welded, b
14、razed,riveted, or soldered joints; friction connections such as pin andsocket connectors or taper pins, twisted-wire splices; andconnections made with screws, or bolts and nuts betweenelectrical wiring and components. The definition excludesrelay contacts, slip rings and commutators, and switches an
15、dcircuit breakers.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 May 10, 2002. Published July 2002. Originallypublished as B 539 70
16、. Last previous edition B 539 01.2Annual Book of ASTM Standards, Vol 02.04.3Annual Book of ASTM Standards, Vol 14.02.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2 Descriptions of Terms for Levels of Electrical Loading:3.2.1 dry
17、 circuitThis method provides for measurementof contact resistance under very low levels of electricalexcitation, with applied voltages and currents selected to be toolow to cause breakdown of thin oxide films or other contami-nates in the contact interface or to cause formation of metallicbridges ac
18、ross the interface where none may otherwise exist.Dry circuit testing is intended to determine whether the testcontact will function properly in circuits of arbitrarily lowlevels of electrical excitation. Dry circuit testing proceduresshould be used when the possibility of films or contaminants inth
19、e 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 samples at high levels ofelectrical loading.3.2.2 rated currentThe rated current for a static contactdevice is determined or specified by the ve
20、ndor or user of thedevice. The rated current may be large enough to causesignificant heating of the test samples. When rated currentmeasurements of contact resistance are required, using eitherac or dc test currents, the procedures outlined for temperaturestabilization in 9.5.3 must be followed.4. S
21、ummary of Test Methods4.1 The test methods described herein are characterized asfour-terminal resistance measuring techniques, wherein a mea-sured and controlled test current is introduced into the sampleusing two“ terminals” or connecting points, and two otherpoints are selected on the sample acros
22、s which a voltage dropis measured. This voltage drop, divided by the test current, isthe effective overall resistance of the sample included betweenthe voltage probes. The voltage-measuring points are chosen soas to measure as closely as possible the voltage drop due onlyto the contact resistance of
23、 the sample and to eliminate fromthe measurement as much as possible the resistance of themetal pieces comprising the contact and the resistance of thewires and connections used to introduce the test current into thesample.4.2 Two different levels of test current are specified. Thechoice of which le
24、vel to use is governed by the application andrequirements of the electrical connection being tested. Elec-tronic signal-circuit connections may require low-level (dry-circuit) testing, whereas power-handling wire connectorsshould be tested at rated current.4.3 Either ac or dc test currents may be us
25、ed, with appro-priate instrumentation.5. Significance and Use5.1 As stated in Terminology B 542, contact resistance iscomprised of a constriction resistance and a film resistance.When present, the latter of these is usually much greater invalue and dominates the contact resistance. For a given conta
26、ctspot, when the film resistance is zero or negligible the contactresistance for that spot is nearly the same as the constrictionresistance and therefore, as a practical matter, has a minimumvalue which represents a clean metal-to-metal contact spot. Asreal contact surfaces exhibit varying degrees o
27、f roughness, realcontacts are necessarily composed of many contact spots whichare electrically parallel. In practical cases the clean metal-to-metal contact spots will carry most of the current and the totalcontact resistance is primarily dependent on the size andnumber of metallic contact spots pre
28、sent (see Note 1). Inaddition, acceptably low values of contact resistance are oftenobtained with true areas of contact being significantly less thanthe apparent contact area. This is the result of having a largenumber of small contact spots spread out over a relatively largeapparent contact area.NO
29、TE 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 Contacts by Holm.45.2 The practical evaluation and comparison of electricalconnections depend in large part on their contact resistancecharact
30、eristics. On the one hand, the absolute value of contactresistance is greatly dependent on the amount of metalliccontact established and indicates initially how efficient thesystem is in producing areas of metallic contact. On the otherhand, a comparison of the initial resistance to the resistanceaf
31、ter aging indicates how stable the system is in maintainingthe initial contact area. Both of these characteristics should beconsidered when evaluating contact systems. The criteriaemployed in evaluating contact resistance and stability are nota part of these test methods as they depend on specificap
32、plications and therefore, will not be quantitatively stated.However, an estimate of contact resistance4resulting fromgood metallic contact can be made for a given physicalsituation and used as a comparison to actual measurements todetermine how effective the system is in establishing stablemetallic
33、contact. Resistances measured by these methodsbefore, during and after simulated life tests are used as a meansof determining the stability of contacts within a device.6. Interferences6.1 Measurement of Low Resistance:6.1.1 Contact resistances are normally very small, rangingfrom microohms to a few
34、milliohms in cases of practicalinterest. The measurement of resistance in this range requiresspecial techniques to eliminate effects of thermal potentials,external interference, and resistance of connections and wiresleading to the test sample.6.1.2 The resistance-measuring procedures in these testm
35、ethods are four-terminal techniques. Test current in thesample is measured and controlled, and made independent ofthe sample resistance. Voltage-measuring probes are attachedto the sample so as to eliminate the effects of connections of thesample into the test circuit. If the purpose of the measurem
36、entis to determine the contact resistance, the voltage measuringprobes are attached as close as feasible to the static contacts, soas to include as little of the bulk resistance of the sample aspossible in the measurement of the contact resistance.6.1.3 Two wire measurements of resistance are not su
37、itablebecause connections to the sample will contribute part of themeasured resistance, and these may be large, unknown, andvariable.4Calculations and formulae for contact resistance of various types of contacts arecovered very thoroughly in Holms Electric Contacts, 4th Edition, Springer-Verlag,New
38、York.B53902e126.1.4 Because the resistance being measured is often in themicroohm or milliohm range, and it is determined by measur-ing the potential across the static contacts, the value of thepotential is often in the microvolt or millivolt range. As aresult, thermal potentials may be significant
39、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, high potential may change aresistance by breaking down a film. Appropriate caution isrequired to obtain valid dry circuit resistance measurementsinc
40、luding 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 Either method described herein can be used with ac ordc test currents, with appropriate changes in instrumentation tocorrespond with the power supply. The
41、 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 unlessotherwise defined in the test report. Take appropriate measuresto isolate the measurements from stray signals, especially sixtyhertz power line nois
42、e. Commercial resistance measuringinstruments that use ac test currents generally are suitableproviding that they meet other requirements of the standard.7. Apparatus and Test Circuits7.1 Fig. 1 shows the basic arrangement of a four wire circuitfor measuring. In the illustration, the measured resist
43、ance is theresistance between the points where the voltmeter is attached tothe test specimen, that is, between the points of V1 and V2. Themeasured resistance includes the contact resistance at thecontact between the two rounded points and the bulk resistanceout to the point where the voltage probes
44、 touch the testspecimen. To measure connection resistance, move the voltageprobes away from the contact point to the very end of eachcontact member where the current leads are attached. Toattempt to measure contact resistance, move the voltage probesas close as possible to the contact point. The equ
45、ipmentconsists of the following elements:7.1.1 Power SupplyA supply capable of providing therequired current and, in the case of the dry circuit measurementcapable of limiting the current to 100 milliamps and the opencircuit voltage to 20mV. The supply may be dc or ac, but thevoltage measuring devic
46、e 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 methods withrespect to accuracy or precision. External metering should beused when necessary.7.1.3 Both output terminals of the dc supply must beisolat
47、ed from the power line, the case of the supply, and thebuilding ground. This prevents “ground loops” or undesiredconnections through ground, between the power supply andother measuring instruments (such as an electronic voltmeter)attached to the sample.7.1.4 The maximum current required in the power
48、 supplycan be estimated from Table 1, which gives rated currents forvarious wire-size terminations according to Military specifica-tions.7.1.5 The output current of the power supply should bevariable and readily and accurately adjustable.7.2 Current Measuring Devicea meter, ac or dc, to matchthe pow
49、er 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 SwitchSince millivolt-drop readings acrossthe sample are to be taken with both forward and reverse dccurrent, a double-pole-double-throw switch of suitable
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