1、Designation: B539 18Standard Test Methods forMeasuring Resistance of Electrical Connections (StaticContacts)1This standard is issued under the fixed designation B539; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、 revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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 connections such aswire
3、 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 berequired in specific cases.
4、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 appropriateSafety Data Sheet (SDS) for this product/material as provided
5、by the manufacturer, to establish appropriate safety, health,and environmental practices, and determine the applicabilityof regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in t
6、he Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2B542 Terminology Relating to Electrical Contacts and TheirUseE122 Practice
7、 for Calculating Sample Size to Estimate, WithSpecified Precision, the Average for a Characteristic of aLot or Process3. Terminology3.1 Definitions:3.1.1 See Terminology B542 for definitions of contactresistance, film resistance, and constriction resistance.3.1.2 bulk resistance, nthe resistance a c
8、ontact 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 probes as close to the contact inte
9、rface as practical.3.1.3 connection resistance, nthe resistance from the ter-mination 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 pr
10、inted circuit pathelectrically connects to the terminal. This resistance is thevalue of resistance displayed by the device in a circuitapplication.3.1.3.1 DiscussionThe term contact resistance is oftenused in commercial literature to indicate the connection resis-tance displayed by the device in a s
11、tandard 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 theexternal circuitry. Measurement of co
12、ntact resistance indepen-dent of all bulk resistance is very difficult for most commercialdevices.3.1.4 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
13、 applied voltage (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.3.1.5 open-circuit voltage, nthe steady-state voltagewhich would appear across
14、 the contacts if they were opened.3.1.6 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,1These test methods are under the j
15、urisdiction of ASTM Committee B02 onNonferrous Metals and Alloys and are the direct responsibility of SubcommitteeB02.11 on Electrical Contact Test Methods.Current edition approved Nov. 1, 2018. Published December 2018. Originallyapproved in 1970. Last previous edition approved in 2013 as B539 02 (2
16、013).DOI: 10.1520/B0539-18.2For 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 ASTM website.Copyright ASTM International, 100
17、Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Rec
18、ommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1welded, brazed, riveted, or soldered joints; friction connectionssuch as pin and socket connectors or taper pins, twisted-wiresplices; and connections made with screws, or bolts and nutsbetween electrica
19、l wiring and components. The definitionexcludes relay contacts, slip rings and commutators, andswitches and circuit breakers.3.2 Descriptions of Terms for Levels of Electrical Loading:3.2.1 dry circuit, nThis method provides for measurementof contact resistance under very low levels of electricalexc
20、itation, 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 across the interface where none may otherwise exist.Dry circuit testing is intended to determine whether t
21、he 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 inthe contact interface exists or when the test sample is ulti-mately intended for use in a low-level circui
22、t. This testing mustprecede other tests on the same samples 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 t
23、est 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. Summary of Test Methods4.1 The test methods described herein are characterized asfour-terminal resista
24、nce 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 across which a voltage dropis measured. This voltage drop, divided by the test current, isthe effective ov
25、erall 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 the sample and to eliminate fromthe measurement as much as possible the resistance of themetal piece
26、s 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 level to use is governed by the application andrequirements of the electrical connection being tested.
27、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 used, with appro-priate instrumentation.5. Significance and Use5.1 As stated in Terminology B542, conta
28、ct 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 contactspot, when the film resistance is zero or negligible the contactresistance for that spot is nearly t
29、he 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 of roughness, realcontacts are necessarily composed of many contact spots whichare electrically paralle
30、l. 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 present (see Note 1). Inaddition, acceptably low values of contact resistance are oftenobtained with true
31、 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.NOTE 1The term metallic contact as used here is intended to includethe so called quasi-metallic contact
32、spots as well. The latter case wasdiscussed in Electric 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 size an
33、d distribution ofthe metallic conducting spots within the apparent area ofload-bearing contact. On the other hand, a comparison of theinitial resistance to the resistance after aging indicates howstable the system is in maintaining the initial contact area. Bothof these characteristics should be con
34、sidered when evaluatingcontact systems. The criteria employed in evaluating contactresistance and stability are not a part of these test methods asthey depend on specific applications and therefore, will not bequantitatively stated. However, an estimate of contact resis-tance3resulting from good met
35、allic contact can be made for agiven physical situation and used as a comparison to actualmeasurements to determine how effective the system is inestablishing stable metallic contact. Resistances measured bythese methods before, during and after simulated life tests areused as a means of determining
36、 the stability of contacts withina 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 e
37、ffects of thermal potentials,external 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 r
38、esistance. 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 measurement3Calculations and formulae for contact resistance of various types of contacts arecovered very thoroughly in Holms Electric
39、 Contacts, 4th Edition, Springer-Verlag,New York.B539 182is 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 resistanc
40、e.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.6.1.4 Because the resistance being measured is often in themicroohm or milliohm range, and it is determined by me
41、asur-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 in relation to thepotential being measured and appropriate measures are re-quired to cancel or eliminate their effects.6.1.5 In
42、 the dry circuit method, 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
43、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 methods are describedas using dc test currents, and the following comments applywhen ac is used.6.2.2 ac measurements should b
44、e expressed as RMS unlessotherwise 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 re
45、quirements 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 resistance is theresistance between the points where the voltmeter is attached tothe test specimen, that is, between the points of V1
46、 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 touch the testspecimen. To measure connection resistance, move the voltageprobes away from the contact point to the very end o
47、f 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 equipmentconsists of the following elements:7.1.1 Power SupplyA supply capable of providing therequired current and, in the case o
48、f 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 device must match the type of current fromthe supply.7.1.2 Voltmeters and ammeters built into power suppliesmay or may not meet the
49、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 beisolated 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 current capacity of the power supply must besufficient for the highest rating of the devices being tested.7.1.5 The output current of the powe
