ASTM_F_1681_-_14.pdf

Designation:F168114Standard Test Method forDetermining Current Carrying Capacity of a MembraneSwitch Circuit1This standard is issued under the fixed designation F1681;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 test method covers the determination of the currentcarrying capacity of a conductor as part of a membrane switch.1.2 This test method may be used to test a circuit todestruction,that is,to determine its maximum current carryingcapacity,or it may be used to test the ability of a circuit towithstand a desired current level.1.3 This test method applies only to static conditions,anddoes not apply to contact closure cycling of a membrane switchunder current load(test method forthcoming).1.4 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 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2F1578 Test Method for Contact Closure Cycling of a Mem-brane SwitchF1680 Test Method for Determining Circuit Resistance of aMembrane Switch3.Terminology3.1 Definitions:3.1.1 conductor resistancethe measured electrical resis-tance through a circuit loop between two test points.3.1.2 DiscussionWhen a switch is included in that loop,itshall be closed”in accordance with Test Method F1680.3.1.3 current carrying capacity(CCC)the maximum levelof electrical current that a circuit can conduct without sustain-ing damage.3.1.4 membrane switcha momentary switching device inwhich at least one contact is on,or made of,a flexiblesubstrate.3.1.5 power capacityelectrical power is defined as cur-rent voltage=V I(watts).3.1.6 test pointstwo preselected conductive points in acircuit loop,possibly including a switch.4.Significance and Use4.1 Current carrying capacity is used by designers andmanufacturers of electronic interface circuitry to ensure thatthe membrane switch can reliably handle the loads occurring innormal use and under extreme circumstances.A thoroughunderstanding of CCC allows manufacturers to take it intoaccount when developing design rules for membrane switches.4.2 Failures due to exceeding the CCC of a circuit may takethe form of a significant change in conductor resistance,insulation breakdown(shorts),or conductor breakdown(opens).4.3 Since a number of design parameters,such as tracewidth,ink film thickness,and heat transfer(mountingsubstrates,active cooling such as fans)affect the final testresults,any conclusions should only be applied to specificdesigns,rather than to a general combination of materials.4.4 Current carrying capacity tests may be destructive andunits that have been tested should be considered unreliable forfuture use.4.5 Current carrying capacity may be significantly differentfor static loads and dynamic(that is,cycling)loads.Failuremodes are also generally different.4.6 The use of a thermocouple to monitor the temperature ofthe UUT may be helpful to monitor the progress of the test.4.7 Initial expected starting current should be calculated inadvance to prevent damage to test equipment.5.Interferences5.1 The following parameters may affect the results of thistest:5.1.1 Temperature,5.1.2 Relative humidity,1This test method is under the jurisdiction of ASTM Committee F01 onElectronics and is the direct responsibility of Subcommittee F01.18 on MembraneSwitches.Current edition approved Jan.1,2014.Published January 2014.Originallyapproved in 1996.Last previous edition approved in 2007 as F168107a.DOI:10.1520/F1681-14.2For 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 5.1.3 Heat transfer characteristics of mounting substrates,5.1.4 Active cooling,5.1.5 Imperfection or variation in conductor deposition,5.1.6 Inconsistencies in the homogeneity of the conductor.6.Hazard6.1 The user must be aware of the operating range of theirequipment to prevent damage to the device from overloadduring testing.For example,the current should be adjustedstarting from a minimum setting,and a decade box should starton the highest rating.7.Apparatus7.1 Controlled current and voltage source,capable of sup-plying sufficient current for the range in question.7.2 Suitable Meter(s),capable of measuring current andresistance(with range appropriate to the test).Do not apply avoltage greater than the intended operating range of the circuitunder test.7.3 Suitable Device,to apply a