1、Designation:B49700(Reapproved 2012)Standard Guide forMeasuring Voltage Drop on Closed Arcing Contacts1This standard is issued under the fixed designation B497;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.
2、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 guide describes recommended procedures to accu-rately measure voltage drop across current carrying contactsand the parameters to be
3、documented in order to effectivelyrecord the results.Such contacts normally carry current greaterthan 1 amp.The applicability of these procedures to contactscarrying smaller currents should be evaluated prior to applica-tion to such devices.Contacts carrying small current may alsobe evaluated using
4、Test Method B539 to measure contactresistance.1.2 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 Da
5、ta 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.For specific precautionarystatements,see Section 6.2.Referenced Documents2.1 ASTM Standards:2B539 Test Meth
6、ods for Measuring Resistance of ElectricalConnections(Static Contacts)B542 Terminology Relating to Electrical Contacts and TheirUse3.Terminology3.1 Terms shall be defined in accordance with TerminologyB542.4.Instrument Selection4.1 Generally,a low-impedance instrument will give greateraccuracy.Since
7、,these instruments are subject to seriousdamage by over-voltage,such as may occur when contacts areaccidentally opened,due care should be taken in a properinstrument range selection.Many of the high-impedancemeters,such as some electronic voltmeters,are not damaged byovervoltage and when used with t
8、he precautions pointed out inthis recommended practice can be quite accurate.Instrumentsmay also be protected by using the voltage-limiting circuit atthe instrument input.Two types of meters are generally usedand can be classified as self-contained voltmeters,or voltme-ters that require an external
9、power source.5.Significance and Use5.1 This guide covers the factors to be controlled,precau-tions and documentation necessary to measure and report thevoltage drop across closed current-carrying contacts.Thevoltage drop is an indication of the efficiency of the contactinterfaces in carrying a speci
10、fied current.This efficiency can beadversely effected by any insulating areas within the contactinterface.Circuits which involve substantial current and lowindependence can be influenced by this contact property.6.Instrumentation Precautions6.1 If a self-contained instrument is used,the followingpre
11、cautions should be observed:6.1.1 The voltmeter leads should be connected as shown inFig.1 as close to the test contacts as possible.6.1.2 The leads should be as short as possible,or calibratedwith the meter,and shielded to reduce the effect of straypick-up voltages.6.1.3 The voltmeter input impedan
12、ce should be 1000 orless.This will load the circuit sufficiently to reduce the effectsof stray-voltage pickup in the instrument leads.The inputimpedance of high-impedance meter can be reduced by placinga 1000-resistor,B,across its input terminals as shown in Fig.1.6.1.4 Before measurements are made,
13、the voltmeter leadsshould be shorted together at point C.With the voltmeter leadsshorted in this position,the test current should be caused toflow in the circuit.If the voltmeter deflects,it may be causedby induction from the load circuit to the internal components ofthe meter.This may be minimized
14、by orienting the meter,orrelocating the meter(that is,moving it away from the circuit)until minimum meter deflection is observed.If necessary,placeconductive shielding between the meter and the circuit.1This guide is under the jurisdiction of ASTM Committee B02 on NonferrousMetals and Alloys and is
15、the direct responsibility of Subcommittee B02.11 onElectrical Contact Test Methods.Current edition approved May 1,2012.Published May 2012.Originallyapproved in 1969.Last previous edition approved in 2006 as B497 00(2006).DOI:10.1520/B0497-00R12.2For referenced ASTM standards,visit the ASTM website,w
16、ww.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 6.2 If a electronic voltmeter requiring an external powersupply is used,the additional precautions listed below shouldbe observed:6.2.1 To determine if the ground-loop impedance,illustratedby resistance A in Fig
