ASTM_F_3291_-_17.pdf

Designation:F329117Standard Test Method forMeasuring the Force-Resistance of a Membrane ForceSensor1This standard is issued under the fixed designation F3291;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 force versus resistancemeasurement of a membrane force sensor(MFS)where theelectrical resistance decreases as the force on the sensor isincreased.1.2 An MFS may or may not be electrically open in its staticstate.This depends on the attributes required for the applica-tion.If the MFS has a measureable resistance in static state,itwas most likely designed to be used as a variable resistor,notas a normally open switch.Ahigh but measurable resistance,instatic state,may still be considered an open switch if theresistance is above the closed resistance threshold recognizedby the interface electronics.1.3 Specialprintedconductivepolymerinksorcharacteristics,or both,of the sensor design are used in MFSto achieve variable resistance when compressed.As force isapplied to the MFS the resistance continues to decrease,but notlinearly,until a point where additional force does not changethe resistance appreciably.Ideally,when force is removed fromthe MFS the resistance will return to,or close to,its originalvalue.1.4 Materials other than conductive polymers can be used inan MFS and also exhibit reduced resistance with increasingforce.1.5 This test method should not be confused with TestMethod F2592 for measuring the force-displacement charac-teristics of a membrane switch(MS)that is designed formomentary closure.Although the resistance of a MS doeschange during contact closure the change from high resistanceto contact resistance is very sudden and additional force doesnot have a significant effect on the resistance;that is,an MS isnot designed to be used as a variable resistor.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the 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:F2592 Test Method for Measuring the Force-Displacementof a Membrane SwitchF1578 Test Method for Contact Closure Cycling of a Mem-brane Switch3.Terminology3.1 Definitions:3.1.1 force at initial measurable resistance(Fim),nforceat Rim.If there is a measurable resistance Rim at Fss then bothFss=Fim=0.3.1.2 initial measurable resistance(Rim),nresistance ofMFS without force applied(if measurable)or the first measur-able resistance when test probe begins applying force.3.1.3 maximum sensor force(Fmaxs),na special maxi-mum force to be applied to MFS during test or the force atwhich no appreciable change in resistance is noted,also knownas saturation resistance.3.1.4 maximum sensor pressure(Pmaxs),nFmaxs/surfacearea of test probe in contact with MFS.3.1.5 membrane force sensor(MFS),nsimilar in construc-tion to a non-tactile membrane switch(MS)but the measuredresistance is designed to decrease as force applied is increased.Also sometimes referred to in the industry as a force sensingresistor.3.1.6 membrane switch(MS),na momentary switchingdevice in which at least one contact is on,or made of,a flexiblesubstsrate.3.1.7 pressure at initial measurable resistance(Pim),nFim/surface area of test probe in contact with MFS.3.1.8 Rmaxs,nresistance at Fmax.3.1.9 test probe tip diameter(Dtp),ndiameter of the testprobe tip(or actuator)that is in contact with MFS during test.3.1.10 zero force steady state(Fss),nsteady state condi-tion before test begins,no probe force applied,Fss=0.If thereis a measurable resistance Rim at Fss then Fim is also 0.1This test method is under the jurisdiction of ASTM Committee F01 onElectronics and is the direct responsibility of Subcommittee F01.18 on PrintedElectronics.Current edition approved Nov.1,2017.Published November 2017.DOI:10.1520/F3291-17Copyright ASTM International,100 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 Recommendations issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.1 4.Significance and Use4.1 An MFS has similar properties to a load cell or straingauge.However,an MFS is not suitable for precision measure-ments.4.2 MFS pressure versus resistance data can be calculated ifthe force probe is providing uniform pressure over a distributedarea or if the sensor is exposed to measurable air or hydraulicpressure.4.3 MFS