1、Designation: F3291 17Standard 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 revis
2、ion. 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 d
3、ecreases 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, nota
4、s 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 Special printed conductive polymer inks orcharacteristics, or both, of the sensor desi
5、gn 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
6、 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
7、(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 va
8、riable 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 Tech
9、nicalBarriers 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 (Fi
10、m), 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 s
11、pecial 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 cons
12、truc-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
13、 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 f
14、orce 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
15、.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
16、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.14. Significance and Use4.1 An MFS has similar properties to
17、 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 force-r
18、esistance plotted results are not linear andresults may change when exposed to repeated force cycles Test Method F1578. It is useful to note that the force-resistancecurve models closely to mathematical form of y =1/x.4.4 Static forces may contribute to drifting test results (alsoknown as creep).5.
19、Interferences5.1 The switch samples should be mounted on a rigidsupport in order to get a more accurate representation of theforce and resistance.6. Apparatus6.1 Test Probe, made of non-elastic material with a flat tipsized 50 - 80 % of the minimum spacer area opening or asspecified. Apply to the fl
20、at tip a silicone rubber pad (recom-mended 65 Shore A Hardness 0.020 in. thick).6.2 Test Surface, to be flat, smooth, unyielding and largerthan MFS under test.6.3 Force Application Device, suitable to hold test probesecurely and provide perpendicular movement into and awayfrom MFS under test, and to
21、 apply all force data points.6.4 Resistance Measure Device, that is, ohm meter. Thedevice should not apply a voltage outside the operating rangeof the MFS contacts.7. Procedure7.1 Pre-test Setup:7.1.1 Ensure that the test specimen is mounted securely to arigid substrate.7.1.2 Connect sensor terminal
22、s to resistance measuringdevice.7.1.3 Record test probe diameter and durometer.7.1.4 Position test probe over designated test area of sensor.7.1.4.1 Record position of test probe on sensor (normallywould be center of sensor).7.1.5 Position probe until tip is just above the top surface ofthe sensor w
23、ithout touching.7.1.6 Precondition sensor at a specified force between 5 to25 cycles, and it is recommended that the instrument and testprobe be used when practical.7.2 In-Process Test:7.2.1 Record resistance if measurable at F0 static state (ifnot measurable resistance record as “open”).7.2.1.1 Exa
24、mple 1: at F0, Rim = open7.2.1.2 Example 2: at F0, Fim =0,Rim = 50 K ohms.7.2.2 Begin applying force to sensor (at a speed not toexceed analog to digital conversion or introduce noise throughmechanical inertia through test probe if using an automatedsystem) until first measurable resistance on the r
25、esistancemeasurement device is registered.7.2.2.1 Record force as Fim, and record resistance as Rim.7.2.3 Continue applying force at predetermined force inter-vals.7.2.3.1 Record data at first interval after Fim as F1, andcorresponding resistance as R1.7.2.3.2 Continue recording data at each force i
26、nterval as R2,F2 Rx, Fx.7.2.4 Continue applying force until Fmaxs is achieved orwhen there is no longer any appreciable change in resistance.7.2.4.1 Record resistance at Fmaxs as Rmaxs.8. Calculations8.1 For pressure versus resistance (if desired)8.2 Calculate pressure at all resistance measurements
27、 = F/Area of test probe tip.8.2.1 Record as P1, P2. Px.9. Precision and Bias9.1 PrecisionIt is not possible to specify the precision ofthe procedure in Test Method F3291 for measuring the forceversus resistance because inter-laboratory studies have proveninconclusive due to insufficient participatin
28、g laboratories withthe appropriate equipment.9.2 BiasNo information can be presented on the bias ofthe procedure in Test Method F3291 for measuring the forceversus resistance because no standard sample is available forthis industry.10. Report10.1 Report the following information:10.1.1 Temperature,1
29、0.1.2 Humidity,10.1.3 Barometric pressure,10.1.4 Probe material, diameter, Shore A hardness,10.1.5 Description of test apparatus,10.1.6 Description of test specimen and the location of testprobe contact location on sensor; normally test would be centerof sensor,10.1.7 Probe tip area,10.1.8 Rim,10.1.
30、9 Fim,10.1.10 Fmaxs,10.1.11 Rmaxs,10.1.12 Resistance versus force data and pressure data (ifrequired) in table form (example Fig. 1) or plotted curves, orboth (example Fig. 2 and Fig. 3),10.1.13 Velocity of test probe if automated system is used,10.1.14 Preconditioning force and number of cycles.11.
31、 Keywords11.1 force-sensitive resistor; force sensor; FSR; membranesensor; membrane switch; pressure sensor; resistive sensorF3291 172FIG. 1 Force and Pressure versus Resistance (example tableform not all data points shown)FIG. 2 Resistance versus Force example graph formF3291 173ASTM International
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35、 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. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585
36、(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:/ 3 Resistance versus Pressure example graph formF3291 174
