ASTM_B_667_-_97_2014.pdf

Designation:B66797(Reapproved 2014)Standard Practice forConstruction and Use of a Probe for Measuring ElectricalContact Resistance1This standard is issued under the fixed designation B667;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last 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 This practice describes equipment and techniques formeasuring electrical contact resistance with a probe and thepresentation of results.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.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 this 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:2B542 Terminology Relating to Electrical Contacts and TheirUse3.Terminology3.1 DefinitionsMany terms used in this practice are de-fined in Terminology B542.3.2 Definitions of Terms Specific to This Standard:3.2.1 contact resistance,nthe resistance to current flowbetween two touching bodies,consisting of constriction resis-tance and film resistance.3.2.1.1 DiscussionConstriction resistance originates in thefact that mating surfaces touch in most cases at only their highspots,which are often called“asperities”or,more commonly,a-spots.The current flow lines are then forced to constrict asthey funnel through these tiny areas.If oxide films or otherinsulating layers interfere with these metal-to-metal contacts,the contact resistance will be higher than when such layers areabsent(see 4.4 for bulk resistance limitation).3.2.2 contact resistance probe,nan apparatus for deter-mining electrical contact resistance characteristics of a metalsurface.Probe,in this instance,should be distinguished fromthe classical tool whose function it is to touch or move anobject.4.Significance and Use4.1 Electrical contact resistance is an important characteris-tic of the contact in certain components,such as connectors,switches,slip rings,and relays.Ordinarily,contact resistance isrequired to be low and stable for proper functioning of manydevices or apparatus in which the component is used.It is moreconvenient to determine contact resistance with a probe than toincorporate the contact material into an actual component forthe purpose of measurement.However,if the probe contactmaterial is different from that employed in the component,theresults obtained may not be applicable to the device.4.2 Information on contact resistance is useful in materialsdevelopment,in failure analysis studies,in the manufacturingand quality control of contact devices,and in research.4.3 Contact resistance is not a unique single-valued propertyof a material.It is affected by the mechanical conditions of thecontact,the geometry and roughness of contacting surfaces,surface cleanliness,and contact history,as well as by thematerial properties of hardness and conductivity of bothcontacting members.An objective of this practice is to defineand control many of the known variables in such a way thatvalid comparisons of the contact properties of materials can bemade.4.4 In some techniques for measuring contact resistance it isnot possible to eliminate bulk resistance,that is,the resistanceof the metal pieces comprising the contact and the resistance ofthe wires and connections used to introduce the test current intothe samples.In these cases,the measurement is actually of anoverall resistance,which is often confused with contact resis-tance.1This practice is under the jurisdiction of ASTM Committee B02 on NonferrousMetals and Alloys and is the direct responsibility of Subcommittee B02.11 onElectrical Contact Test Methods.Current edition approved Oct.1,2014.Published October 2014.Originallyapproved in 1980.Last previous edition approved in 2009 as B667 97(2009).DOI:10.1520/B0667-97R14.2For 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 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 5.General Description of a Probe5.1 A probe generally includes the following:5.1.1 Fixtures for holding specimens of varied size andshape and for attaching electrical leads to them.5.1.2 A mechanism that applies a measurable load to thespecimen that can be increased,decreased,or held constant.5.1.3 A shock mounted table to prevent any