Kistler Manual
Contents
1. TYPE 9261A MULTI COMPONENT MEASURING PLATFORM FOR BIOMECHANICS AND INDUSTRY 9261A B6 926le_ 12 74 2 OPERATING INSTRUCTIONS MULTI COMPONENT MEASURING PLATFORM FOR BIOMECHANICS AND INDUSTRY Table of Contents Section Page Table of Contents angen see cteec torsion oa eae ae a ee 2 T DESCRIPTION Tiersen eens Sree Ta nT ne SUR Nr Neem TE ee eee Semen SER eer 4 1 1 PROC ONS serene ee eek A te ual nee oop EO ER hei Ue 4 K2 Fechnicaldatan 6 cscs eaten n e teal tacts T E ER 5 1 3 Explanations tothe Technical dataene oneone inenen eeaeee eeann Eae 6 1 3 1 Rano oh ere ee rere E E E E a e a E 6 1 32 OANE OF La PEPERIT EEEE EEEE 6 1 3 3 Calibrated TANTES inno ee oe E E R ro ero ei 7 1 3 4 SY Ys TITRA ig Nae RS ee E ERE E EE E EEE ee 7 1 3 5 Sensi vity VaATIALIONS 23 cistec be c2ecsecc Pes a E Prsctvesteecbrccleesicacles Perales clvacPesctecstee stasis eich es 7 1 3 6 Linearity aera ere ee eet at am ts A enc Seren mn mn Len ed ee 7 1 3 7 dc Rigi fas Rel ibs une aieng ene eae Mae eats eee a ant ee Ae ne rt eee eee eet ae as aa 8 e Sma O11 23 a Co Ka me RP Ee ore eee 9 Be CTO TA E caie hates aigas se ctiasosiauc avednevdesuies staipais octianes gucanssans epaties Seuss ollausssnctausbarassstules 9 1 3 10 Natural frequency eee ce eC ee ean SCO rR cee ee ee eee 9 1 3 11 Thermal sensitivity SII saccaci cn cteacatasetaranaeeaetureast aaatewase canes seaenens aes eans amen uanrman anne eae 9 1 3 12 Influence of Cable capacitan C2. Long Time Constant Amplifier to Operate The disappearance of F person steps off the platform can also be registered 9261A B6 926le_ 12 74 18 4 SIGNIFICANCE AND PROCESSING OF THE OUTPUT SIGNAL 4 1 Nomenclature ax az Fy Fxg Fy Fy Fz Fz4 Nx Distance between transducer axes and y axis for 9261A a 132 mm Coordinates of the intersection point of the line of action of the resultant with the x y plane translated parallel by az working plane Distance between working plane and x y plane Distance between transducer axes and y axis for 9261A b 220 mm Resultant of all forces acting on the platform Components of the resultant Force components in x direction acting on transducers 4 Force components in y direction acting on transducers 1 Force components in z direction acting on transducers 1 4 A Resultant moment vector after reducing all acting forces and moments to the origin of coordinates Components of the resultant moment vector Free moment vector resulting from all acting free moments Components of the resultant free moment vector Origin of coordinates Normal mechanical stresses in the test object measuring platform interface a gt 0 corresponds to compression Reference coordinate system 9261A B6 926le_ 12 74 19 Figure 9 Definition of the measurands 4 2 Reference coordinate system A positive Cartesian coordinate system is used as referen
3. N b Cross talk F gt M 3 Nm kN means that under a load of say F 1 KN a cross talk signal appears at the M output corresponding to a genuine Mz signal of 3 Nm On this platform with its four force transducers the cross talk is dependent also on the position of the force application point but it is always within the specified limits 1 3 10 Natural frequency The platform forms a complex oscillatory system In practice the lowest natural frequency observed is dominant all channels for this platform it is a diaphragm oscillation of the top plate 1 3 11 Thermal sensitivity shift This value describes the behaviour of the quartz element itself i e it is a material property of quartz Since for example a temperature change of 50 C shifts the sensitivity by only 1 or so this effect can be ignored in most cases 1 3 12 Influence of cable capacitance The cable capacitance and hence the cable length have practically no influence on the measured result if the prescribed special cables and KIAG SWISS charge amplifiers are used 1 3 13 Time constant For quasi static measurements a knowledge of the time constant to be expected is important This depends on the measuring range selected on the charge amplifier and varies from about 100 s in the most sensitive range to about 100 000 s in the least sensitive range see operating instructions for 9261A B6 926le_ 12 74 10 charge amplifier Type 5001 1 4 Constructio
4. amplifier must have extremely high insulation gt 100TQ and low frictional electricity Consequently special cables must be used exclusively see data sheet 15 01 1 Ordinary cables may be used from the charge amplifiers to the indicating instruments The electrical connectors should always be handled with great care and cleanliness The protective caps of the plugs should only be removed immediately before connecting 9261A B6 926le_ 12 74 15 Note The plug protection caps of the platform are best screwed to those attached to the connecting cables e g Type 1619 by chains In this way they cannot get lost or dirty inside If contacts or insulation get dirty they can be cleaned with Freon TF Type 1001 or white gasoline The insulation resistance can be measured with a teraohmmeter e g KIAG SWISS Type 5491 3 2 Switching possibilities on the platform The measuring platform has eight outputs see Fig 7 Between the outputs relating to the same coordi nate axis are switches enabling the adjacent outputs to be paralleled or separated Highly insulating reed relays are employed as switches operated by a permanent magnet rotatable from outside Switch positions Screw slot horizontal Switch closed Screw slot vertical Switch open Important The switches between outputs connected to a charge amplifier each must not be closed otherwise the amplifier will go into saturation at once If outputs are needed from only one or t
5. of 7 5 pC N and a range 20 N V 2 x 10 mechanical units volt Time constant to long Load platform centrally either by standing on it steadily or placing a mass weighing about 50 kg on it and note the voltmeter reading Minimum reading under load indicates good positioning of the platform If more than 5 V is shown by pressing lightly with the fingers find the corner that still needs shimming The reading should remain 5 V when the force application point is moved within the measuring surface After making the fine adjustments the platform can be secured with the mounting angles see Fig 6 S re Figure 6 Mounting plate It is advisable to use the washers under the M10 mounting bolts as this minimizes the danger of the mounting angles getting damaged or turned out of position 9261A B6 926le_ 12 74 14 Important The mounting angles are not intended to clamp the platform down the floor only to prevent it from shifting Before screwing on therefore check whether the angles can be pressed onto the supporting surface with the fingers With correct fitting this should be possible and the foam rubber will be pressed only lightly While the M10 mounting bolts are being tightened up press on the fixing angle constantly with the fixing angles to make sure that this does not cant The voltmeter must not respond to the tightening of the fixing angles If it does the angle in question is jammed It is advisabl
6. whose inherent accuracy can be exploited and retained only if 9261A B6 926le_ 12 74 11 it is properly installed and treated In particular it is absolutely essential that the mounting instructions are observed strictly and exactly if damage due to overloading e g excessive internal stresses etc is to be avoided The makers disclaim all responsibility for damage when the mounting instructions are not followed properly 2 2 Mounting base The special advantage of piezoelectric force measurement smallest measuring deflections even under the largest forces i e high rigidity means also that the platform is very sensitive to inadequately accurate support Consequently it must be mounted only on a very rigid base such as a mounting base see also 2 4 The measuring platform stands on the base with four circular supporting surfaces which are concentric with the four transducers To ensure a perfect support a special frame of hot galvanized steel is supplied with the platform If this frame is grouted into a concrete pedestal according to instructions all requirements for the measuring platform support are met and it can be mounted without difficulty Procedure for concreting in the mounting frame e Inspect the frame for any damage in transit before grouting it in Make sure that it is square and that the flat steel forming the frame has not been bent e Insert the four stone bolts see Fig 5 and secure with the lock nuts
7. 1 the free moment about an axis parallel to the z axis can also be determined M Mz Fy ax Fy ay 24 4 4 Processing the output signals Depending on the number of components desired up to eight charge amplifiers may be needed to convert the output signals of the measuring platform into analog voltages Here it may be recalled that the individual outputs can be added together directly by means of the switches provided e g for 1 2 and 3 i e the three force components In this case only three charge amplifiers are needed see Fig 10 A For processing 10 11 and 12 on the other hand one charge amplifier each must be used for outputs whore sum and difference are required The various formulae derived under 4 3 can then be calculated either analogously or digitally For the analog calculation special summing amplifiers Type 5217 and analog dividers Type 5215 are available If all six variables Fx Fy Fz ax ay and M are to be determined the Electronic Unit for 6 component Force Measurement Type 9803 may be used This contains all the necessary equipment 8 charge amplifiers 2 summing amplifiers and 1 analog divider see Fig 10 D The various extension phases of a measuring system are shown in Fig 10 A For measuring the three force components Fx Fy and F Primarily for simpler measurements in sport and gait analysis B For determining the coordinates a and ay of the center of gravity of
8. 13 Figure 7 Connections and switches of the platform eesesesseesssessesrssesresesresresesresreresresreesrenreresresrsrest 15 Figure 8 Measuring small dynamic changes in a large fundamental force sssssseeeseeeseessrseeesreserese 17 Figure 9 Definition of the Meas urands soca tect cotati ha cee ahd ee ks Sa Se ahd a i a a te 19 Figure 10 Layout of typical measuring SYSteMS ceeeesceseeseceseeesceeseeceseceeecseeeeseceseeeseeesseeeeeeteeees 25 Tables Table 1k Techritcal dA a a a oiea 5 9261A B6 926le_ 12 74 1 DESCRIPTION 1 1 Introduction The multi component measuring platform Type 9261A is a piezoelectric transducer with which the following measurands can be determined e the 3 components F F and F of the applied force F e the 2 coordinates a and a of the point of force application e the free moment M about an axis normal to the platform surface The four 3 component quartz transducers fitted give the platform a high rigidity thus minimal measuring deflections and wide frequency range The electrical charges yielded by the platform are strictly proportional to the measurands They are converted by charge amplifiers into analog dc voltages after which they can be recorded displayed or otherwise processed as required The measuring platform Type 9261A is employed primarily for investigations in biomechanics sport orthopedics neurology ergonomics etc and in industry automotive engineering et
9. a person standing on the platform and measuring the force component F Employed mainly for Romberg tests and other investigations into posture control posturography statokinesimetry 9261A B6 926le_ 12 74 24 C Note 1 The unused outputs for F and Fy on the platform are to be short circuited e g with short circuit cover Type 1875 See also under 3 2 D Note 2 This system is suited only for the applications named where the horizontal forces Fx and FY are very small In all other cases expansion to configuration C is necessary E Combination of A and B Measures the three force components Fx Fy and F as well as the coordinates ax and ay of the momentary force application point Suited for all application areas F Like C but measures the free moment M in addition Versatile system with unlimited application potential For further information about these instruments the appropriate operating instructions should be consulted The analog output voltages of the charge amplifiers range 10 V may also be processed digitally When choosing A D converters make sure in particular that they are sufficiently fast so that the frequency range is not narrowed 9261A B6 926le_ 12 74 25 B6 9261e 12 74 12 Seal eee a0 X344 a Yisa En l gt i a ig Fy You l A F Zi Degen gt i z Zo I i i L 5802 Z4 7 7 m B c D L Charge ampl
10. c Figure 1 Multi component measuring platform for biomechanics and industry Type 9261A 9261A B6 926le_ 12 74 1 2 Technical data Figure 2 Dimensions of the measuring platform measuring surface hatched 440 x 264 mm2 Table 1 Technical data Ranges Each axis loaded separately force application Fx Fy each kN 3 point inside measuring surface work plane not Fz KN 0 10 more than 100 mm above platform surface AX mm 200 Le az lt 137 mm Ay mm 300 M z Fx Fy 0 kNm 2 5 Overload 120 Overload for each range loaded singly The measuring platform installed according to instructions see Section 2 cannot be damaged by a human being in ordinary civilian or sports clothing without tools Calibrated ranges Fx Fy each KN ass Fz KN 0 10 9261A B6 926le_ 12 74 6 Sensitivities nominal values Fx Fy each PC N 7 5 Fz PC N 3 3 Sensitivity variations Force application point within measuring surface lt 2 indicated Force application point within the whole top plate lt t 5 Linearity all ranges FSO lt 1 Hysteresis all ranges FSO lt 0 5 Threshold Fx Fy Fz MN lt 50 Cross talk F lt gt Fy lt 42 Fx y gt F lt 3 Fz gt Fx y lt Operating temperature range C 0 50 Thermal sensitivity shift oC 2 10 Natural frequency without additional coverings lowest observed Hz gt 200 Insulation resistance each channel TQ gt 10 Capacitance p
11. ce coordinate system The z axis is normal to the platform surface and the positive direction points into the platform The positive y axis points towards the end with the connections A positive Cartesian coordinate system is defined as follows Looking in the direction of the positive x axis a rotation of the positive y axis through 90 into the positive z axis appears clockwise Similarly the positive moment vector M constitutes a clockwise rotation looking in the direction of the positive x axis The same is true of the y and z axes by cyclic rotation 4 3 Correlations between forces and moments acting on the measuring platform and output signals Note The following individual transducer outputs are paralleled permanently and are designated and defined as measuring platform outputs as follows Output 9261A B6 926le_ 12 74 Xis Eina xi x2 Xara Fa Eti Ying Faa N F Ia Byra via HE F F F 1 2 3 4 E Pig EE Snu i ge Resultant 1 F F F F determined by the angle y to the x y plane siny F and the angle 6 of the projection of F onto the x y plane to the positive x axis tan F X or determined by the direction cosines angle a between the resultant and the positive x axis es COS angle B between the resultant and the positive y axis zs p cosp F angle y between the resultant and the positive z axis cosy JF Note cos a cos B cos y 1 Compone
12. e Beside each stone bolt is a mounting bolt 4 for the measuring platform This must remain screwed in during grouting The threads must be greased beforehand so that the bolts can be loosened again afterwards e Place the frame in the prepared concrete foundation e Level the frame exactly with a precision spirit level The supporting surfaces must lie in the same horizontal plane to within 0 1 mm Check also the diagonals of the four supporting points 6 440 x 264 mm e Grout the foundation without moving the frame from its exact position It is advisable to leave the upper cross members projecting a little above the surrounding concrete surface e Make sure that the grout goes tightly under the upper cross members e Check once again that the supporting points are in the horizontal position as prescribed Important If the platform is installed outdoors the concrete foundation must be bedded in gravel at a frost proof depth Leave sufficient space for the mounting angles at both sides of the platform see Fig 5 A duct for up to eight connecting cables must be provided at the appropriate end of the platform in the direction of the positive y axis The cables are in flexible metal tubing of 10 mm outside diameter and should not be bent with a radius of less than 50 mm If the facility of direct switch cover at the platform is to be exploited a removable cover should be provided so that the switches can be operated with a screwdr
13. e action line of the resultant with a a ax ay and az as the coordinates of a point running on it The point of force application is thus simple to find it is enough to determine the intersection of the action line with a given plane Example For the working plane of the measuring platform Type 9261A the equation is a 37mm 17 This value has only to be substituted in equation 16 to obtain the coordinates ax and ay of the force application point in the working plane In the general case however there are free moments acting on a multi component measuring system as well System 16 then appears as follows 0a F a F a M M 18 F_ea 0 a F ea M M F ea F a 0 a M M 9261A B6 926le_ 12 74 22 The measuring system can measure only Fx Fy Fz Mx My and Mz see equations 1 2 3 10 11 and 12 Though the components and M M y and M of the free moment vector are contained in the components Mx My and Mz of the resultant moment vector their magnitude is not known In other words Since M M and M are not known the constants of system 18 also remain unknown The equation system 18 not only determines the action line of the resultant therefore but also comprises all straight lines parallel to the action line Or to put it in another way yet In the general case it is impossible to say of a measured moment whether it is generated only by a force eccentr
14. e to provide a covering frame around the platform covering both the cable duct and the mounting angles Important The platform must be protected against direct sunlight otherwise thermal expansion may overload the very rigid force transducers due to internal stresses 2 4 Special mountings In certain applications maximum forces occur that are well below the maximum ranges This is particularly true with investigations outside the field of sport such as in orthopedics rehabilitation neurology etc In such cases the platform may also be laid on relatively softer floors such as linoleum The following instructions must then be observed however The floor must be the same under all four supporting surfaces same material same elasticity The floor must be plane to within 1 mm The platform must rest only at the four supporting points It must be installed exactly as described in sub section 2 3 though in this case the fixing angles can be omitted e The forces applied must not exceed 25 of the ranges If any question or doubts arise with such applications the makers or their representatives must be consulted 3 OPERATION 3 1 Basic circuitry of the measuring system The electrical charges in pC yielded by the measuring platform are converted by charge amplifiers into proportional voltages which can then be indicated recorded or otherwise processed with the usual equipment The connecting cables from the platform to charge
15. er connection switches open or closed pF lt 400 Specifications for installation surface on which measuring platform is mounted see Sub section 2 2 Platform material Cast aluminum Weight kg 26 1 3 Explanations to the Technical data The terms and their definitions are based largely on ISA standards Instrument Society of America The notation ISA refers to the standard ISA S 37 1 1969 Definitions with the notation KIAG have been created by us specially for our instruments 1 3 1 Ranges Range ISA The measurand values over which a transducer is intended to measure specified by their upper and lower limits All specifications are maintained within the range Because this instrument measures simultaneously in 3 axes the ranges indicated for the individual components can be fully exploited only if one component at a time acts as load With combined loadings the admissible ranges are reduced see also 1 3 2 In critical cases the makers or their representatives should be consulted 1 3 2 Overload Overload ISA The maximum magnitude of measurand that can be applied to a transducer without causing a change in performance beyond specified tolerance 9261A B6 926le_ 12 74 7 For use in biomechanics the overload is not only given as range percentages because in practice it is not possible for example to ask an athlete to load the platform only within certain limits The platform has been designed so that it cannot su
16. er range limits 1 3 7 Hysteresis Hysteresis ISA The maximum difference in output at any measurand value within the specified range when the value is approached first with increasing and then with decreasing measurand Quartz itself has a virtually non measurable hysteresis Owing to the mechanical assembly a measur able hysteresis may occur but in every range it lies below the stated percentage of the particular FSO If more hysteresis is detected this means that the platform has not been mounted property 9261A B6 926le_ 12 74 9 1 3 8 Threshold Threshold ISA The smallest change in the measurand that will result in a measurable change in transducer output With piezoelectric transducers the threshold is limited by the inherent noise of the transducer and above all that of the charge amplifier The stated value of the measurand corresponds to about 3 times the noise signal of a usual charge amplifier 1 3 9 Cross talk Crosstalk KIAG Signal at an output of a transducer in response to a measurand not assigned to that output Cross talk is expressed as the ratio of the measurand corresponding to that output signal to the measurand causing the cross talk If both measurands have the same dimension the cross talk can be expressed as a percentage Examples a Cross talk Fx gt F 0 8 means that under a load of say Fx 100 N a cross talk signal appears at the F output corresponding to a genuine F signal of 0 8
17. es icicseiucs aware uv asetecatececan eter elueasecuson eer etusetiaeteumtentuateunean tas 9 Kads Eme CONSLANL aes TEA nwa A nO eu ARARA AA R EEAS 9 1 4 Construction of the measuring platOriiy vn accsheeynesteereenebantyenibeereenhbeckvareheeeuodenekenestnetionebieatant 10 IS Examples of applications nenien 24 GA Gasau asta ii asis iis tiist i sadias dis oiss tilasas isos iie 10 2 ANSTALLA TION ie cccosececsdasssscadsescansdessdensdescdecsdaceiecsduosdoaidosscasbescdessdecalessieesdesidesssoudeessiwnttbcalestoause 10 2 1 General inf rmation Rememeee mane aetna arene ee i ree eet ne ng ne eee ere en er 10 5 sami 1 SBR A EDT Ea 0221 aaa ce era ea ae a CU rn re nen eee aa 11 2 3 Mounting the measuring platform aicicescctcck th cak ak tak ae Ce ena a ed ad ee ae 12 2A Special Monno Sannen tat tet tats a het R bet et tate tat patient tat ten tat bat bth b bai 14 La TOPERA TION T oa ae are rs teenie eae aren an sean near ean sean ore na O 14 3 1 Basic circuitry of the Mme ASUnit SS y SLSI 5 gc iss vase sass cana insswane etn acivarisa wovendiie cinerivaunseveuieoauasathovtawans 14 3 2 Switching possibilities on the platform sxc civic ance aoemiveutaacaaraleeaevenvck aman 15 3 3 Switching the system for 1 2 or 3 force components 2 0 eeeeeeeeeteeeeeeeseeeseeceeceseeeseeeeaeeeaee 15 3 4 Switching the system for measuring additional components cceeceeeseceseeeseeeeeeeneeeneeees 16 3 5 Range selection and resolution cccecescccssscces
18. ic to the origin of coordinates or only by a free moment or by any combination of the two Special case of measuring platform Type 9261A No free moments M and M can act on the platform thus M M 0 Why In the intended applications of the measuring platform standing walking running driving rolling jumping on and off it no tensile stresses are imposed on its surface i e the interface test object measuring platform 0 20 19 from which it also follows that Fz foz dA 2 0 20 On the other hand a free moment M x or M y would impose tensile stresses too 6 lt 0 because a free moment can always be represented by a force couple two parallel forces equal but of opposed signs But as long as the condition oz 2 0 is fulfilled no force couple forming M or M can arise For the measuring platform Type 9261A the equation system 18 can therefore be written as follows 0 a F a F a M F a 0 a F a M F a F a 0 a M M 9261A B6 926le_ 12 74 23 From the first two equations the coordinates ax and ay of the intersection of the action line of the resultant with the x y plane shifted by az can now be determined directly a D ee Fea M 22 F F 23 Eea M a The value of a is known it is the distance of the working plane parallel to the x y plane from the coordinate origin With ax and ay now known from the appropriately resolved third equation of 2
19. ifier e g 5001 S Summing amplifier 5217 D Analog Divider 5215 Specia cables 1582 1584 1597 Fig 10 Layout of typical measuring systerns Figure 10 Layout of typical measuring systems 9261A B6 926le_ 12 74 26 5 CALIBRATION AND MAINTENANCE 5 1 Calibration 5 1 1 Works calibration At the works the platform is calibrated in the positive Fx Fy and F directions the forces being introduced through a ball oil a hydraulic testing press 5 1 2 Subsequent calibration Where the requirements with regard to measuring F are particularly exacting the platform may be calibrated in situ by placing known weights on it The sensitivity of the F and Fy channels can be determined in the following improvised way e place a rubber mat on the platform e acarefully place a weight of about 50 200 kg on it e by means of a steel wire and e g a spring balance a horizontal pull can now be exerted on this weight keeping the force application point as low as possible Of course calibration is possible only up to the shear force given by the effective friction 5 2 Maintenance parts list Apart from keeping the TNC connections and the other parts clean the measuring platform needs no maintenance f the platform has obviously been damaged e g transducers destroyed by overloading it must be repaired and tested at the maker s works
20. iver Between the platform and the surrounding floor a gap of at least 2 mm must be left Floor coverings 9261A B6 926le_ 12 74 12 such as Tartan must likewise be interrupted at the edge of the measuring platform to prevent any parasitary force shunts TRL A h 1 iy SE SR Y Figure 5 Installing the measuring platform Measuring platform 9261A Mounting frame Mounting angle Mounting bolts with washers Stone bolt with hexagon nut Supporting surfaces of platform 40 mm diameter Shim to take up any play Concrete foundation Cable duct 0 Minimum height 60 mm total height according to selected covering e g Tartan a ON aAa 2 3 Mounting the measuring platform Clean all supporting surfaces properly e Place the platform in position e Press lightly with the fingers to check whether the platform has diagonal wobble 9261A B6 926le_ 12 74 13 If there is discernible play this must be rectified by shimming a set of shims is supplied Only one corner should need shimming normally If the thickness grading of the sheets supplied is not sufficient the residual play can be taken up with household type aluminum foil Fine adjustment is achieved as follows Open switch between connections Y 1 4 and Y2 3 screw slot vertical see Fig 8 At Y 4 connect a charge amplifier and an indicating instrument e g voltmeter preferably with a range 10V 10 V Adjust the charge amplifier to a sensitivity
21. line is determined as follows see Fig 3 to make things clearer the curve has been distorted in the direction of the ordinate 9261A B6 926le_ 12 74 FSO 100 J Linearit t 90 Lin arite s a FSO Linearity Hysterese Hyst r sis 70 Hysteresis 60 Beste Gerade Droite optimale Best straight line Ausgangssignat Signal de sortie Transducer Output S B 8 1 o 10 20 350 40 50 60 70 80 90 100 Messgr sse Grandeur mesur e Mesurand Figure 3 Linearity Two parallels are sought lying as close together as possible and enclosing the entire calibration curve In addition a third parallel midway between the first two must pass through the zero no force no output signal The slope of this mid parallel is the sensitivity of the transducer Half the distance between the two parallels measured in the direction of the ordinate and expressed as a percentage of the full scale output is the linearity This definition describes the independent linearity with forced zero Although the quartz itself yields an electrical charge exactly proportional to the load certain unavoidable deviations result from the mechanical assembly In each partial range including the un calibrated ones the linearity remains within the percentage stated for the end value of the partial range in question FSO means full scale output i e the algebraic difference between the outputs corresponding to the measurands at the upper and low
22. n of the measuring platform Figure 4 Cross section through the measuring platform The measuring platform is shown in cross section in Fig 4 Four 3 component force transducers 1 Type 9251 are pre stressed between the base plate 2 and the top plate 3 with the pre stressing bolts 4 The space between the two plates is sealed with a special rubber strip 5 At one end there are eight TNC connectors 6 With switches 7 that can be operated from outside all switching combinations can be selected for measuring up to three force and three moment components Figs 8 9 and 1 0 The platform has four supporting surfaces 8 concentric with the four transducers see Section 2 1 5 Examples of applications Examples applications for the multi component measuring platform in biomechanics and industry are e Investigations in biomechanics e g measuring the forces exerted by the human foot in walking standing etc Orthopedic investigations Monitoring of rehabilitation progress e g with prostheses after fractures etc Investigations for sport e g optimizing sequences of movements to achieve top performance Neurological investigations e g Romberg test psychomotor activities etc Measuring reaction forces between car tires and ground Dynamic and static determination of coefficients of friction e g between shoes and different floor coverings 2 INSTALLATION 2 1 General information The platform is a measuring instrument
23. nts of the resultant moment vector referred to origin of coordinate M WF F F F My a F F F F NS I A F F a E E M42 2314 Y4 Y 243 20 1 2 3 4 5 6 7 8 9 10 11 12 9261A B6 926le_ 12 74 21 Generally a multi component force and moment measuring system yields not more than the 3 components of the resultant its direction in space though not its position and the 3 components of the resultant moment vector referred to the origin of coordinates In other words Only the resultant translated through the coordinate origin and the resulting moment vector referred to the origin of coordinates are obtained Let us take the equations for determining the resultant moment vector M see Fig 9 M a eF a ek M 13 14 M a F aeF M y a zZ a x y 15 Mysa ie ad and assume for the time being that no free moments are acting on the measuring system i e M M y M 0 Since Fx Fy Fz Mx My and Mz are measured by the system for determining ax ay and az equations 13 14 and 15 can be rewritten as follows 0 a F a F a M 16 F a 09a F a M Fea F 9a 0 a M Z The determinant of this system equals 0 because all coefficients of the main diagonal are equal to 0 i e the system is indeterminate for ax ay and az Because it is a linear equation system however it determines a straight line i e th
24. seceeseeeeseeeeseecsseeeeneecessecesseeceeseeesseeesseeeseaaees 16 4 SIGNIFICANCE AND PROCESSING OF THE OUTPUT SIGNAL 18 Ard INOMENCIALULCseyssiticete e ovate ea AA Aaa lel levele REAA EEEE 18 4 2 Reference coordinate SYStem cccccessccssssceessccsseceeseecesseeensneceneeceeseeessneeeeeeceeeeessseeeeseeeseaes 19 4 3 Correlations between forces and moments acting on the measuring platform and output signals 19 4 4 Processing the output signals 4 cracaraceirssseeanetawtecuntaateaiostindacentoaenteeereeenanetencsensnmeamnmnanedmereeets 23 5 1 Calibration e a Men arene A ee ee A E ere I ee ae oe A A 26 5 1 1 Works calibrations ees eae men NRE Senne oe ne Ne aaa oe gee aT Te Ren eR RS Anaa 26 5 1 2 SUD Se QUCIIENC Al ORAL ON aiei e n E EE E E eters E 26 5 2 Maintenance parts stierranone E E A E ERE E ES 26 9261A B6 926le_ 12 74 3 ILLUSTRATIONS AND TABLES Page Figures Figure 1 Multi component measuring platform for biomechanics and industry Type 9261A 4 Figure 2 Dimensions of the measuring platform measuring surface hatched 440 x 264 mm2 5 P iea EAMG Any a aa a As Dome Ae 8 Figure 4 Cross section through the measuring platform essssssessesssssssssssssrssrestssrssesseestessrssesseeseesse 10 Figure 5 Installing the measuring platform esssssesssessssssesssesesssrsstssrestestsstssreseesressreseestessessesseeseesese 12 Figure 6 Mounting D F11 SALAA EEEE EEE EEEE EEEE EET
25. stain damage if used for its intended purpose provided it is installed properly Thanks to the special properties of piezoelectric transducers measured values falling unintentionally outside the range but still inside the overload are usable in most cases 1 3 3 Calibrated ranges These ranges are calibrated individually at the works The results are recorded on calibration sheets which are issued with the instruments The high linearity of quartz transducers allows the same values to be used for partial measuring ranges see also 1 3 4 1 3 4 Sensitivity Sensitivity ISA The ratio of the change in transducer output to a change in the value of the measurand Here the slope of the best straight line through the zero is given as the sensitivity see 1 3 6 The sensitivities quoted here are nominal figures Each instrument is accompanied by individual calibration sheets giving the exact values see also 1 3 3 and 1 3 5 Because the sensitivity of each instrument is constant over wide ranges the same sensitivities are valid also for partial measuring ranges 1 3 5 Sensitivity variations When the measuring platform is installed according to the instructions the sensitivity will vary no more than specified provided the force application point remains within the limits stated 1 3 6 Linearity Linearity ISA The closeness of a calibration curve to a specified straight line For piezoelectric force transducers this straight
26. to the values corresponding to the selected measuring range N V An excellent feature of piezoelectric measurement is that small force changes can be measured very accurately in the presence of a high preload For this it is enough see Fig 8 after applying the preload e g a person steps onto the platform to switch the amplifier to reset select a range of appropriate sensitivity and then switch the amplifier back to operate Even the smallest forces can then be registered dynamically e g by cathode ray oscilloscope such as movements of a finger or in extreme cases the force changes resulting from the pulse i e the ballistocardiogram 9261A B6 926le_ 12 74 17 AF f t Figure 8 Measuring small dynamic changes in a large fundamental force Tomm QW CASS Amplifier to Reset range selected for F 100 N V amplifier to Long Time Constant Amplifier to Operate Fz js applied person steps onto platform After reading or recording the weight switch amplifier to Reset once more The charge corresponding to F is thus eliminated Switch over to more sensitive range for A F e g 1 N V Select Short Time Constant Set amplifier to Operate The variations A F can now be measured with great accuracy because the dynamic threshold is about 0 02 N i e a A Fz of 0 02 N as a change in F 800 N now gives an output voltage of about 20 mV Amplifier to Reset Switch back to less sensitive range 100 N V
27. wo axes the outputs belonging to the coordinate axis not in use must be paralleled and short circuited with a short circuit cover Type 1875 If this is not done the measurement may be falsified by electrical cross talk Figure 7 Connections and switches of the platform FOOD 442 3 4 1440 243 1 2 3 4 3 3 Switching the system for 1 2 or 3 force components This is the simplest operating mode All switches on the platform must be closed i e screw slots horizontal see Fig 7 A charge amplifier and a connecting cable are needed for each of the three channels Fx Fy and F It is immaterial whether the cable of the Fx channel is connected X12 or X34 for instance the same applies to Fy and F 9261A B6 926le_ 12 74 16 Each of the three amplifiers is to be adjusted to the respective sensitivity given on the calibration sheet 3 4 Switching the system for measuring additional components By opening switches on the platform and switching in further amplifiers up to six components can be measured The complete correlations and possibilities are dealt with in detail in Section 4 3 5 Range selection and resolution It is best to use charge amplifiers with calibration factor adjustment for the measuring platform such as the KIAG SWISS charge amplifier Type 5001 The sensitivities are adjusted according to the values for the Fx Fy and F channels quoted in the calibration sheets In this way the output voltage is adjusted directly
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