1、Designation: B497 00 (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 rev
2、ision. 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 parame
3、ters to be 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 ev
4、aluated using 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 appropriateM
5、aterial 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. For specific precautionarystatements, see Section 6.2. Referenced Documents2.1 ASTM S
6、tandards:2B539 Test Methods 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 wil
7、l give greateraccuracy. Since, 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
8、 byovervoltage and when used with the 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
9、 voltme-ters that require an external 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
10、the contactinterfaces in carrying a specified 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-c
11、ontained instrument is used, the followingprecautions 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 straypi
12、ck-up voltages.6.1.3 The voltmeter input impedance 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 a
13、s shown in Fig.1.6.1.4 Before measurements are made, 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 t
14、he internal components ofthe meter. This may be minimized 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 jurisdicti
15、on of ASTM Committee B02 on NonferrousMetals and Alloys and is 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: 10.152
16、0/B0497-00R12.2For 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 D
17、rive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesNOTICE: This standard has either been superseded and replaced by a new version or withdrawn.Contact ASTM International (www.astm.org) for the latest information16.2 If a electronic voltmeter requiring an external powersupply is used,
18、the additional precautions listed below shouldbe observed:6.2.1 To determine if the ground-loop impedance, illustratedby resistance A in Fig. 2 is detrimental to the meter short theinstrument leads to each other at point C. If the meter gives adeflection with the leads so connected when contact curr
19、entflows, the following steps must be taken to remove thedisturbance:6.2.1.1 Eliminate the ground loop formed by the connec-tions of the electronic voltmeter to the power line. This loop isshown by the broken line in Fig. 2. It can be completed throughinterwinding capacitance of the instrument power
20、 transformer.This capacitance effect can be reduced by placing an additionalisolation transformer between the measuring instrument andthe source of instrument power (Fig. 3).6.2.1.2 An optional technique that can be used to eliminatethe effect of the ground loop, is to use a differential voltmeter.A
21、 differential voltmeter is an analog device that continuouslymeasures the difference between two potential levels withrespect to ground as a reference point.7. Factors Affecting Voltage Drop7.1 Quite often, contact-voltage drop will change with time.On such an occasion, it is best to wait until the
22、voltage hasstabilized to record the value.FIG. 1 Voltmeter ConnectionsFIG. 2 Ground Loop ImpedanceFIG. 3 Elimination of Ground LoopB497 00 (2012)27.2 Contact-voltage drop variations can be expected whenthe contact material-softening voltage is reached.7.3 Contact resistance and, therefore, contact-v
23、oltage dropmay be affected by the current flowing through the contacts atthe time the measurement is made. For this reason, test currentsshould be specified.7.4 For d-c measurements, thermocouple potentials pro-duced by dissimilar metallic junctions, such as meter lead tocontact junction, may influe
24、nce some meters. One method topartially compensate for this is to take readings, reverse thepolarity of the contact-current source, and take additionalreadings. By taking the average value of readings made in bothpolarities, the thermal effect is eliminated.7.5 Consideration should be given to the r
25、esistance ofcircuit components between the voltmeter leads, since they actas a baseline resistance to which the contact resistance isadditive.8. Reporting Results8.1 Reports of voltage drops should include:8.1.1 Test currentThe current must be stable at the timethe voltage drop is read.8.1.2 Power s
26、ourceac or dc. For ac the frequency andpower factor should be recorded.8.1.3 Timing of voltage measurement(s)For example:8.1.3.1 When stable.8.1.3.2 At a fixed time after current initiation.8.1.3.3 Averaged over a range of time.8.1.4 Contact characteristics:8.1.4.1 Material.8.1.4.2 Size.8.1.4.3 Shap
27、e.8.1.5 Contact force.8.1.6 Meter typeManufacturer and model.9. Keywords9.1 closed arcing contacts; voltage dropASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advis
28、ed that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either r
29、eapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If
30、you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individu
31、al reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 00 (2012)3
