Kistler 9041C Owner's manual

Brand: Kistler

Model: 9041C

Type: Owner's manual

Instruction

Manual

9001C_002-928e-12.20

Piezoelectric Force Sensors,

Ring Force Transducers

Types 9001C ... 9091C,

9101C ... 9107C,

9130C ... 9137C

Page 1

9001C_002-928e-12.20

Thank you for choosing a Kistler quality product charac-

ter ized by technical innovation, precision and long life.

Information in this document is subject to change without

notice. Kistler reserves the right to change or improve its

products and make changes in the content without

obli gation to notify any person or organization of such

changes or improvements.

by various intellectual property rights. For more details visit

www.kistler.com. The Kistler Group includes Kistler Hol-

ding AG and all its subsidiaries in Europe, Asia, the Ameri-

cas and Australia.

Kistler Group

Eulachstrasse 22

8408 Winterthur

Switzerland

Tel. +41 52 224 11 11

info@kistler.com

www.kistler.com

Foreword

Piezoelectric Force Sensors, Ring Force Transducers

9001C_002-928e-12.20Page 2 Page 39001C_002-928e-12.20

Content

1. Introduction .................................................................................................................................4

2. Important instructions ................................................................................................................5

2.1 For your safety ....................................................................................................................5

2.2 Disposal instructions for electrical and electronic equipment .............................................6

2.3 Unpacking ...........................................................................................................................6

2.4 Notes on handling the sensor .............................................................................................6

2.5 Tips on use of manual ........................................................................................................7

3. General .........................................................................................................................................8

3.1 Applications ........................................................................................................................8

3.2 Sensor design and principle of operation ...........................................................................9

4. Mounting ....................................................................................................................................11

4.1 General aspects of mounting ...........................................................................................11

4.1.1 Pretension and preload .......................................................................................11

4.1.2 Sensor in direct path of force ..............................................................................13

4.1.3 Sensor in force shunt .........................................................................................13

4.2 Structural design and force contact ..................................................................................14

4.2.1 Examples .............................................................................................................14

4.3 Effect of elasticity conditions on the measurements .........................................................17

4.3.1 Calculations related to engagement of force .......................................................18

4.3.2 Examples .............................................................................................................21

4.4 Mounting example ............................................................................................................24

4.5 Installation of sensor family 90x1C and 910xC ................................................................25

4.5.1 Type 9422A: mounting for compression forces only ...........................................25

4.5.2 Type 9420A: Mounting for both compression and tensile forces.........................27

4.6 Installation of big force sensors Type 9081C and 9091C .................................................29

4.7 Installation of a Slimline Sensor Types 9130C … 9137C .................................................30

4.7.1 Direct force path mounting ..................................................................................30

4.7.2 Type 9410A: mounting in force shunt mode ........................................................31

5. Measurement .............................................................................................................................33

5.1 Basic arrangement of a measuring system ......................................................................33

5.2 Range selection and threshold .........................................................................................34

5.3 Measuring high-frequency phenomena ............................................................................35

5.4 Measuring quasistatic phenomena ...................................................................................35

5.5 Instructions and safety precautions ..................................................................................36

Total pages 55

6. Calibration and maintenance ...................................................................................................37

6.1 In-Situ calibration of force sensors ...................................................................................37

6.1.1 Working point calibration by peak value comparison ..........................................37

6.1.1.1 Test system requirements ....................................................................38

6.1.1.2 Reference sensor installation ..............................................................38

6.1.1.3 Load application ...................................................................................39

6.1.1.4 Calibration process worksheet .............................................................40

6.1.2 Kistler calibration service.....................................................................................43

7. Troubleshooting ........................................................................................................................44

7.1 Diagnosisandrecticationoffaults ..................................................................................44

7.2 Repairing Load Washer ....................................................................................................45

8. Technical data ...........................................................................................................................46

8.1 Optional accessories ........................................................................................................46

9. Appendix ....................................................................................................................................47

9.1 Glossary ...........................................................................................................................47

9.2 Measurement uncertainty .................................................................................................50

9.3 Linearity ............................................................................................................................51

9.4 Frequency range ..............................................................................................................53

9.5 Inuenceoftemperature ...................................................................................................54

Piezoelectric Force Sensors, Ring Force Transducers Important instructions

9001C_002-928e-12.20Page 4 Page 59001C_002-928e-12.20

1. Introduction

Thank you for choosing a quality product from Kistler.

Please read through this manual thoroughly to enable you

to fully exploit the various features of your product.

To the extent permitted by law Kistler accepts no liability

if this instruction manual is not followed or products other

than those listed under Accessories are used.

Kistler offers a wide range of measurement products

through to turnkey solutions:

Piezoelectric sensors for measuring pressure, force,

torque, strain, acceleration, shock and vibration

Strain gage sensor systems for measuring force and

torque

Piezoelectric pressure sensors and transmitters with

matchingmeasuringampliers

Matching measuring ampliers (charge ampliers, pi-

ezoresistive ampliers, etc.), displays and charge ca-

librators

Electronic control, monitoring and evaluation units as

wellassoftwareforspecicmeasurementapplications

Datatransmissionmodules(telemetry)

Kistler also develops and produces measuring solutions

fortheapplicationeldsengines,vehicles,manufacturing,

plastics and biomechanics sectors.

Our product and application brochures will provide you

with an overview of our product range. Detailed data

sheets are available for almost all products.

If you need additional help beyond what can be found

either on-line or in this manual, please contact Kistler‘s

extensive support organization.

2. Important instructions

It is absolutely essential to follow the instructions below,

which are intended to ensure your safety when working

with the equipment and guarantee a long, trouble-free

service life.

2.1 For your safety

Kistler force sensors have been thoroughly tested and

left the factory in perfectly safe condition. To maintain

this condition and ensure safe operation the user must

follow the instructions and warnings in this manual

Piezoelectric force sensors may only be mounted, used

and maintained by persons familiar with the equipment

andsuitablyqualiedfortheirparticularwork

If it has to be assumed that safe operation is no longer

possible, switch the equipment off and ensure it cannot

be switched on again inadvertently

It must be assumed that safe operation is no longer

possible when the product

shows visible signs of damage,

has been overloaded

is no longer operating,

has been in lengthy storage under unsuitable

conditions

has been subjected to rough transport conditions.

Mount the ring force transducer as speciﬁed. See section 4

„Mounting“ for details.

Secure all of the parts mounted on the force sensors

against the anticipated forces.

Piezoelectric Force Sensors, Ring Force Transducers Important instructions

9001C_002-928e-12.20Page 6 Page 79001C_002-928e-12.20

2.2 Disposal instructions for electrical and electronic equipment

Do not discard old electronic equipment in municipal trash.

For disposal at end of life, please return this product to

the nearest authorized electronic waste disposal service or

contact your Kistler sales ofﬁce for instructions.

2.3 Unpacking

Check all of the packaging for any damage in transit,

which must be reported to the freight forwarder and the

responsible Kistler distributor.

Please check also for the completeness of the delivery

and report any missing parts to the responsible Kistler dis-

tributor.

2.4 Notes on handling the sensor

The specied environmental and operating require-

ments must be met when working with the sensor

The insulation resistance of piezoelectric sensors is of

criticalimportance;itmustmeetthevaluespeciedin

thedatasheet(upto1014 W).Toachievethisvalueall

plug connections must be kept scrupulously clean and

dry. The insulation resistance can be measured with

the corresponding insulation tester from Kistler

Protect all connector or cable parts between sensor

andchargeamplieragainstanydirt,andinparticular

make absolutely sure you never touch the front of any

connectorwithyourngers.Puttheincludedcoveron

if a connection is not being used

The cable for connecting the sensor to a charge amp-

lierisahigh-insulationtype.Ifnotincluded,useonly

suitable connecting cables or accesories specied by

Kistler

2.5 Tips on use of manual

We recommend that you read through the entire manual

thoroughly. However, if you cannot spare the time and are

already familiar with piezoelectric force sensors of Kistler,

you may skip to the sections with the information currently

required.

We have tried to organize this manual clearly so that the

required information is easily accessible.

Keep this manual in a safe place where it is readily acces-

si-ble at all times.

If you lose your manual please contact your Kistler distri-

butor for prompt replacement.

Piezoelectric Force Sensors, Ring Force Transducers General

9001C_002-928e-12.20Page 8 Page 99001C_002-928e-12.20

3. General

Piezoelectric force sensors are quartz crystal ring force

transducers. The force to be measured is transferred to

the quartz sensor elements via the cover plate and base

plate of the tightly welded steel housing. The quartz ele-

ments produce an electric charge proportional to the me-

chanical load. A charge amplier generates an electric

voltage from this charge. These signals are displayed, re-

corded or processed in the familiar way.

Thanks to the extremely high resolution of quartz it is pos-

sible to measure a change in force of the order of 1 N

under a pretension of several tons.

Theshape(loadwasher)andtherelativelysmalldimen-

sionsallowexibleapplicationandeasymounting.Stan-

dard accessories for special applications or mounting

conditions are available on the datasheets of the corres-

ponding sensor.

Sensitivity(chargeperunitforce)isaconstantofquartz

as a material. The associated threshold is virtually the

same for all the load washers of different sizes.

This has three unique advantages:

High level of overload protection, very small forces can be

measured with one sensor with a large measuring range

High rigidity; a sensor with a larger measuring range un-

dergoes less deformation

Several sensors can be electrically connected in parallel

toasinglechargeamplier.Theoutputsignalisthenthe

sum of all of acting forces

3.1 Applications

Kistler ring force transducers are very rigid and ideal for

measuring dynamic forces. This very high rigidity has ex-

tremely little effect on the dynamic characteristics of the

object being measured, in which they are mounted.

Depending on the size of the force, quasistatic measu-

re-ment can be performed over several minutes or even

hours(thesignaldriftisonlyabout±50mN/s).However,

truly static measurements over any length of time are not

possible.

On the other hand, after a pause of any length a sensor

undercontinuous staticload (forexample, mountedin a

threadedconnection)canbereconnectedtoachargeam-

plierandthechangesinloadthenmeasuredaccurately.

Measurements of dynamic forces (AC mode) are also

possible over any length of time. Kistler load washers

have a virtually unlimited life and are not subject to sensi-

tivity drift caused by aging.

The force to be measured is transferred to the quartz sen-

sor elements via the cover plate and base plate of the

tightly welded steel housing. The quartz elements produce

an electrical charge proportional to the mechanical load.

Thesensitivity(chargeperunitforce,aconstantofquartz

as a material) and hence the threshold is virtually the

same for all of the different sized load washers.

3.2 Sensor design and principle of operation

A piezoelectric ring force transducer consists of one or

two crystal ring washers, an electrode and a housing with

connector(seeFig.1).

The force to be measured must be evenly distributed over

the ring surface. The mechanical compressive stress re-

sults in an electric charge being generated in the quartz

crystal. This charge is proportional to the applied force

and does not depend on the dimensions of the quartz

washers(longitudinalpiezoelectriceffect).

Piezoelectric Force Sensors, Ring Force Transducers Mounting

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Q = Quartz washers

E = Electrode

G = Housing

S = Connector

F = Force acting on the load washer

Fig. 1: Schematic section through a standard piezo-

electricringforcetransducera)andaSlimline

forcesensorb)

The generated charge is conducted from the electrode

and supplied to the plug connection. The polarity is cho-

sen so that a compression force generates a negative

charge, which is then converted into a positive voltage in

thechargeamplier.Thehousingservesasgroundcon-

nection. Unloading of the load washer produces a positive

charge.

Connecting several force sensors in parallel adds the

chargesoftheindividualsensorandthechargeamplier

measures the total force.

To ensure the forces to be measured are distributed even-

ly over the ring surfaces, the contact surfaces on the ob-

jectbeingmeasuredmustbeasat,rigidandnelyma-

chined as possible.

4. Mounting

If something is not clear or difculties are encoun-

tered when mounting piezo ring force transducers,

please contact the responsible Kistler distributor or,

if appropriate, the manufacturer, for advice. To enable

the query to be handled effectively it is important

to describe the measurement problem and provide

drawings or sketches that make the type of load,

engagement and point of application of the force

evident.

4.1 General aspects of mounting

Kistlerloadwashersmustbemountedbetweentwonely

machined(preferablyground),rigid,parallelsurfaces.This

allows force measurement over a wide frequency range.

TherecommendedsurfaceroughnessisRa=1,6μm.

4.1.1 Pretension and preload

Why to apply a pretension or preload:

Between the always imperfect surfaces inside and out-

side the sensor there are microgaps that act as inter-

posed spring elements. Preloading closes these gaps

to ensure force measurement is in the linear range and

freefromdisturbinginuences.(s.Fig.2)

Pretension eventually allows the measurement of both

compressionandtensionforces(s.Fig.3)

An optimal choice of preload allows to operate the sen-

sor in the range, where it is most robust against ben-

ding moments, which is at 50% of the nominal force of

thesensor.(4.3.1Calculationsrelatedtoengagement

offorce)

Pretension presses the contact surfaces together so

that the high rigidity of the sensor can be fully exploited

Piezoelectric Force Sensors, Ring Force Transducers Mounting

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Fig. 2: Linearity of force sensors Fig. 3: Measuring ranges depending on preload

Difference of pretension and preload:

The terms preload and preload force are often used as

synonyms, although they have a crucial difference: A

force is applied to the sensor by both preload and preten-

sion to overcome the nonlinear range of the sensor. How-

ever, when pretensioning a ring force transducer, a screw

is used through the center hole, resulting in a small force

shunt, which is not present with a pure preload. This force

shuntreduces thesensitivity ofthe sensorby ≈5…10%,

depending on the layout.

Fig. 4: Pretension and the resulting force shunt through

bolt

How to preload:

When pretensioning, the force must be measured with the

sensoritself,andthechargeampliersettothesensitivity

speciedinthetechnicaldata.Asthepretensioningbolt

forms a force shunt, after being mounted the sensor

must be recalibrated to determine the sensitivity of the

complete measurement setup.

Calibratedsensorscomewithaspecicsensitivityvalue

for preloading.

4.1.2 Sensor in direct path of force

With direct force measurement almost the entire process

force passes through the sensor.

Fig. 5: Measurement in direct path of force

The total force applied (preload force Fv and process

forceFz)shallnotexceedthenominalforceofaringforce

transducer. Otherwise a bigger sensor has to be chosen.

In general, the force shunt effect of the preloading bolt is

neglectedwhenasensorsizehastobedened.Butifcir-

cumstances require it, the effective load on the quartz by

theprocessforceFzcanbereducedbythese≈5…10%

that are absorbed by the bolt. Check the datasheet of the

bolt accordingly.

4.1.3 Sensor in force shunt

Fig. 6: Example of indirect force measurement

If very large forces are to be measured or the sensor

cannot be positioned directly in the path of the force, it is

often mounted in a force shunt. This arrangement allows

the sensor to be used to solve a wide variety of measure-

ment problems. Due to it’s small dimensions, the Slimline

series 913x is very well suited for this purpose.

Piezoelectric Force Sensors, Ring Force Transducers Mounting

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4.2 Structural design and force contact

The full measuring range can only be exploited if the

force is evenly distributed. The mounting surfaces

should preferably be ground. Accessories like spherical

washers, force distributing rings, insulating washer and

force distributing caps make mounting easier in many

cases(seewww.kistler.com/force).Atthemaximumallo-

wed load of the particular load washer of whatever size a

surface pressure Gmaxofapproximately150N/mm2 ari-

ses.

4.2.1 Examples

The ideal mode of force engagement produces an even

surface pressure on the ring force transducer and is free

from shear forces and moments. Several examples of

how force can be applied most effectively are listed below.

Measurement on rough surfaces

Contactsurfacesmustbeatandrigid.Iftheycannotbe

nely machined, localized overloads and damage to the

surface of the sensor must be avoided by using a force

distributingring(Fig.7).

Fig. 7: Mounting with a force distributing ring Type 95x5

on a rough surface

Measurement of a screw force

When measuring a screw force it is essential to avoid load

casea),as itcausesan overloadattheinside edge.To

ensure accurate measurement and exploitation of the full

measuring range, a matching element for introducing the

force must be manufactured.

Thebearingsurfacesontheloadwashermustbenished

by grinding. A good grease applied at the screw thread

and head (such as Kistler Type 1063) must be used to

reduce the friction.

Fig. 8: Measurement of force in a screw connection;

a)ineffectiveintroductionofforce,b)withcon-

structional element

Measurement of force between roughly machined

and/or oblique surfaces

Measurement between rough and/or oblique surfaces

should be avoided if possible (Fig. 9, case a). Machine

the mounting surfaces, preferably by grinding. A force dis-

tri-buting ring or a spherical washer should only be used

asatemporarysolution(Fig.9,caseb).However,under

load a spherical washer will no longer allow compensation

for misalignment.

Fig. 9: Force measurement between roughly machined

andobliquesurfaces,a)ineffectiveintroduction

offorce,b)withforcedistributingringandsphe-

rical washer

Measurement of a point force

A force distributing cap prevents introduction of force at a

point. If the plate is too thin it is deformed into a dish sha-

peandoverloadstheinsideedgeoftheloadwasher(Fig.

10,casea)inasimilarwaytotherstexampledescribed

(Fig.8,casea)).Asshownincaseb),theforcedistribu-

ting cap provides a remedy.

Piezoelectric Force Sensors, Ring Force Transducers Mounting

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Fig. 10: Measurementofapointforce;a)ineffective

introductionofpointforce,b)withforcedistribu-

ting cap

Measurement of force on a beam with two load

washers

Thedeectionofabeamsupportedontwoloadwashers

can result in local deformation of the washers (Fig. 11,

casea)).AsimpletrussarrangementasshowninFig.11,

caseb)providesaremedy.

Fig. 11: Measurement of force on a beam with two load

washers;a)ineffectiveapplicationofforce,b)

with simple truss arrangement

4.3 Effect of elasticity conditions on the measurements

With pretensioned connections, attention must be given to

the diversion of force without fail.

Fig.12showsitsinuenceasafunctionofthe elasticity

conditions, by means of stress-strain diagrams.

Ideally, the force shunt via the pretensioning elements is

very small, so that almost the entire force to be measured

is transmitted and measured by the load washer.

If the force shunt is large, it is still basically possible to

perform measurements, provided that the setup is calib-

rated. However, there is a risk that the magnitude of the

forceshuntmaychangeduringoperation(forexampleas

material compression, together with changes in tempera-

tureordeformations),andfalsifyingthemeasurementre-

sult despite calibration.

In all cases in accordance with Fig. 12 recalibration with

the washer mounted and pretensioned is necessary.

Examples

a) Theboltusedforpretensioninghasapproximatelythe

same rigidity as the load washer (with surrounding

elements).Eachofthetwopartstakeshalfoftheex-

ternal force F. The load washer only measures 50% of

theactingforceF(Fu=0.5F)

b) Iftheloadwasher(withsurroundingelements)iscon-

siderablymoreexiblethanthebolt,onlyasmallpro-

portion of the external force is measured (Fu <<F).

This solution should be avoided if possible

c) Iftheloadwasher(withsurroundingelements)iscon-

siderablymorerigidthanthebolt(idealcase),almost

theentireforceismeasured(Fu ≈F).Theexactvalue

of the force shunt is determined by the calibration

Piezoelectric Force Sensors, Ring Force Transducers Mounting

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F: External force

FB: Force of the pretensioning bolt

FU: Force of the load washer

f: Elongation

Fig. 12: Effect of the elasticity conditions on the measu-

red result

4.3.1 Calculations related to engagement of force

If the force is applied eccentrically or the object being

measured deforms, bending moments arise. The resultant

bending stress is superimposed on the direct stress. In

thesecasesthemeasuringrangespeciedinthetableof

technical data no longer applies. The maximum allowed

surfacepressureσmaxmustnotbeexceeded.Themaxi-

mumallowedbendingmomentsspeciedinthetechnical

data can be used to determine the total load.

As a load washer cannot take tensile stresses, the direct

stress must always be greater than the bending stress.

The direct stress is produced by the sum of measured

force and pretension force.

Fig. 13 shows the general load case for a load washer,

with the pretension force FV, the axial force F and a side

force FS acting simultaneously.

Fig. 13: Combined load of force and bending moment

If the side force Fs is unavoidable, the following situation

happens:

Relative to the center of gravity of the load washer, the

side force Fs produces a bending moment Fs · h. This re-

sults in the bending stress sB, which is counteracted by

the negative component of the measured force. On this

diagram the measured force F produces a relatively small

direct stress sF(sF < sB).Asaloadwashercannottake

any tensile stress, an additional force Fv must be produ-

ced by means of a pretensioning bolt.

To prevent any tensile stresses forming, the maximum

bending stress sBmax. must remain under 50% of the ma-

ximum allowed direct stress smax.. This means that, in the

presence of the maximum allowed bending stress, the

measuring range of a load washer is reduced to 50%. If

the measured force F is less than 50% of the measuring

range, with a bending stress acting at the same time the

missing force Fv must be applied by means of a pretensi-

oning bolt.

Piezoelectric Force Sensors, Ring Force Transducers Mounting

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It is also necessary to be aware of the requirement that

the side force Fs must not exceed 10% of the direct force

(F + Fv) (based on a coefcient of friction m = 0.1). For

most applications this assumption includes a factor of sa-

fety against sliding of approximately 50%.

From the information in the technical data (Section 8)

(range=Fmax and max. MB),ifthepretensionforceFV and

the measured force F are known it is possible to make a

simpliedcalculationoftheallowedbendingmoment:

Case A Case B

Fig. 14: Load diagram

Case A: Rising range of load diagram

F+Fv ≤ ½ · Fmax

Bending moment MB:

Case B: Falling range of load diagram

F+Fv ≥ ½ · Fmax

If the bending moment is known the maximum allowed

force is determined by the pretension force and the meas-

ured force.

Case A:

Case B:

4.3.2 Examples

Example 1:

A load washer Type 9061C is mounted in the structure of

a machine in order to measure the forces generated, the

congurationissimilartothatshowninFig.13.

The following values are obtained from the technical data

of the datasheet:

Fmax = 140 kN

Mmax = 380 N·m

The load washer was pretensioned with 70 kN, the maxi-

mum allowed measured force is given as 30 kN. Case B

therefore applies. The side force acts at a lever arm of ap-

proximately 0.25 m. With these gures the following are

obtained for the maximum allowed side force:

and

In this example, as the measured force was substantially

less than the pretension force the maximum allowed va-

lues of the bending moment or lateral friction force (see

Example2)arenotexceeded.

Piezoelectric Force Sensors, Ring Force Transducers Mounting

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Example 2:

In the next example a measured force considerably hig-

her than the pretension force is assumed. The side force

FS that produces a bending moment is also acting in this

case.

The technical data gives the following values for the sen-

sor Type 9102C:

Fmax = 50 kN

Mmax = 86 N·m

The measured force F is assumed to be 0 ... 30, the pre-

ten-sion force FV is 5 kN. The lever arm of the side force

FS is given as h = 0.1 m.

As FS acts continuously and independently of F, the worst

case is F = 0, and case A applies

F+ FV≤½·Fmax(CaseA)

and

Tocalculatetheno-slidingconditionthecoefcientof

friction of m = 0.1 is used with the smallest measured force

F = 0:

Fm=(F+FV)·m=(0kN+5kN)·0.1=0.5kN

Theno-slidingconditionissatised,asFS < Fm

Example 3:

The next example shows the case of a measured force

that acts eccentrically. The bending moment results from

the lever arm b. The sensor Type 9102C is considered

again, with the following values:

Fmax = 50 kN

Mmax = 86 N·m

The pretension in this case is given as FV = 10 kN, and

the measured force F is limited to the range 0 ... 30 kN. As

the side force FS is dependent on the measured force F,

case B applies. As the moment is produced by the mea-

suredforce,theformulacanbemodiedtocalculatethe

allowed distance b.

If the full measuring range of the sensor is to be exploited

by the measured force, it must therefore be certain that

the force acts at the center of gravity of the sensor.

Piezoelectric Force Sensors, Ring Force Transducers Mounting

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4.4 Mounting example

An example of mounting a bearing shows the effect of the

way the force is applied and the load path.

In Fig. 15 the load washer has been mounted between

angeandfoundation,oralternativelybetweenangeand

bolt head. If a force acts on the bearing, in the case on

the right the greater part of the force is measured with the

load washer. The proportion involved in the force shunt

approximately corresponds to the ratio of the rigidity of the

load washer on the one hand, to the rigidity of the shank

of the bolt between its head and the foundation on the

other.

The situation is much worse with the alternative mounting

congurationon theleft. If,for example,a forceacts on

the bearing in the direction of the foundation, the bearing

angetakesalmostallofit.Estimationoftheratioofthe

rigidityofthebearingangeonthefoundationontheone

hand, and the rigidity of the bolt with load washer on the

other, quickly makes it evident that the force shunt for the

loadwasheris verysmall.Themorerigid theangethe

lower the proportion of the force that can be measured by

the load washer.

Fig. 15: Example of bearing force measurement

4.5 Installation of sensor family 90x1C and 910xC

4.5.1 Type 9422A: mounting for compression forces only

à use the preloading element set Type 9422A… from

Kistler(includedatsensorsType9001…9051).

à more detailed information about the required setup

(dimensionsetc.)canbefoundinthedatasheetofthe

Type 9422A… .

1. Themountingsurfaceshavetobeat,rigidand

ground.

2. Carefully clean the bearing surfaces on the base

plate, the cover plate and the sensor with a

degreasingcleaner(suchasethanol).

3. Attach the centering sleeve to the screw.

4. Loosely assemble the sensor according to drawing

Fig.16.

a)Optional:putinsulationwashersonthecontact

surfaces of the sensor, if the sensor shall be

mountedground-insulated(Kistleraccessory

Type95x8).

5. Grease sparingly the head and thread of the

preloading bolt with Kistler special grease Type 1063.

(inordertoreducetorquestransmittedtothesensor

duringpreloading).

6. Connectyourchargeampliertothesensorandset

thesensitivitytothevalueprovidedinthedatasheet/

calibrationsheet(fullrangevalue).

7. Applythedesiredpreload(refertochapter4.1.1)by

tightening the screw and checking the resulting force

shownonthechargeamplier.Donotexceedthe

maximum pretension force.

8. Make sure the screw is slightly recessed with regard

to the surface of top and bottom plate.

è do not correct the preload by turning the screw coun-

terclockwise!

è just start preloading again from 0 kN instead!

è Use a new screw in case you exceeded the load limit.

Piezoelectric Force Sensors, Ring Force Transducers Mounting

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Fig. 16: Detailed dimensions for sensor installation are

available on the datasheet of Type 9422A...

4.5.2 Type 9420A: Mounting for both compression and tensile forces

à use the high-strength preloading element set

Type 9420A… from Kistler

à more detailed information about the required setup

(dimensionsetc.)canbefoundinthedatasheetof

Type 9420A…

1. Themountingsurfaceshavetobeat,rigidand

ground.

2. Carefully clean the bearing surfaces on the base

plate, the cover plate and the sensor with a

degreasingcleaner(suchasethanol).

3. Applyanadhesive(e.g.Loctite121)ononeofthe

threads of the bolt.

4. Screw the bolt with the adhesive treated end into the

base plate.

5. Attach the centering sleeve to the screw.

6. Loosely assemble the sensor according to drawing

Fig.17.

a)Optional:putinsulationwashersonthecontact

surfaces of the sensor, if the sensor shall be

mountedground-insulated(Kistleraccessory

Type95x8).

7. Grease sparingly the upper thread of the preloading

bolt and the contact surface of the pretension nut with

Kistler special grease Type 1063.

8. Connectyourchargeampliertothesensorandset

thesensitivitytothevalueprovidedinthedatasheet/

calibrationsheet(fullrangevalue).

9. Apply the desired preload by tightening the screw

and checking the resulting force shown on the charge

amplier.Recommendedpreloadforpressand

tensile forces is around 50% in order to achieve the

highest stability regarding bending moments plus a

decentrangefortensileforces(refertoch.4.1.1).

10. Do not exceed the maximum pretension force of the

bolt. In case you need to reach higher preloads, you

will have to another bolt or contact Kistler for advice.

11. Make sure the bolt ends are not directly exposed

to a force induction. The measured force has to be

distributed by the top and the bottom plate.

è do not correct the preload by turning the screw coun-

terclockwise!

è just start preloading again from 0kN instead!

è Use a new screw in case you exceeded the load limit.

Piezoelectric Force Sensors, Ring Force Transducers Mounting

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Fig. 17: Detailed dimensions for sensor installation are

available on the datasheet of Type 9420A

4.6 Installation of big force sensors Type 9081C and 9091C

Kistler provides two preloading element sets with espe-

cially strong bolts for the big force sensors:

– Type9455(forType9081Csensors)

– Type9456(forType9091Csensors)

Basically, the mounting procedure is the same like in

chapter 4.5.2 with Type 9420, with one decisive diffe-

rence:

è The preload must be applied by a hydraulic press,

before the nut is tightened

Thepreloadof400kN/600kNistoohightobeappliedby

tightening the nut.

Contact Kistler to get your big force sensors Type 9081C

Type and 9091C mounted properly into your own struc-

ture.

Fig. 18: Load washer pretensioned with set

Type9455/9456.Detaileddimensions

are available on the datasheet

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4.7 Installation of a Slimline Sensor Types 9130C … 9137C

Do not allow any grease to get onto the surface of thesensor.

The head bearing surface and thread of the preloading bolt

must be greased before the bolt is screwed in.

4.7.1 Direct force path mounting

1. The mounting surfaces have to be at, rigid and

ground(Fig.9).

2. Carefully clean the bearing surfaces on the base pla-

te, the cover plate and the sensor with a degreasing

cleaner(suchasethanol).

3. Grease sparingly the head and thread of the preloa-

dingboltwithKistlerspecialgreaseType1063.(inor-

der to reduce torques transmitted to the sensor during

preloading).

4. Loosely assemble the sensor according to drawing

Fig. 19.

5. Connectyourchargeampliertothesensorandset

the sensitivity to the value provided in the datasheet.

6. Slowly apply the desired preload (refer to chapter

4.1.1)bytighteningthescrewandcheckingtheresul-

tingforceshownonthechargeamplier.

7. Make sure the screw is slightly recessed with regard

to the surface of top and bottom plate.

è do not correct the preload by turning the screw coun-

terclockwise!

è just start preloading again from 0kN!

è Use a new screw in case you exceeded its load limit.

Fig. 19: Here you can see how the sensor is loosely

assembled.

Mount. dim.

Type

Thread Bore diameter

D1 [mm]

Plate

thickness 1)

A [mm]

9130C... M2,5 2,9 8,0

9132C... M4 4,3 8,0

9133C... M6 6,4 12,0

9134C... M8 8,4 16,0

9135C... M10 10,5 20,0

9136C... M12 13,0 24,0

9137C... M14 15,0 27,0

1)Recommended minimum value

4.7.2 Type 9410A: mounting in force shunt mode

Preferably mount the Slimline sensor with the preloading

boltanddiskType9410A..fromKistler(optionalaccessory).

1. Grindthestructureaccordingtotheexampleing.16

2. Carefully clean the bearing surfaces on the base pla-

te, the cover plate and the sensor with a degreasing

cleaner(suchasethanol).

3. Grease sparingly the head and thread of the preloa-

dingboltwithKistlerspecialgreaseType1063.(inor-

der to reduce torques transmitted to the sensor during

preloading).

4. Loosely assemble the sensor according to drawing

Fig. 21.

5. Connectyourchargeampliertothesensorandset

the sensitivity to the value provided in the datasheet.

6. Applythedesiredpreload(min.20%ofnominalforce)

by tightening the screw and checking the resulting

forceshownonthechargeamplier.

7. Grind the structure and preloading bolt in conjunction

with the mounted & preloaded sensor.

8. Remove the sensor.

9. Re-grindthestructure withoutinfeed(toachievethe

slight projection P and ensure a reproducible force

shuntandgoodlinearity).

10. Perform step 2 … 6 again to install the sensor into the

structure.

11. Make sure that at the end the screw head is slightly

recessed with regard to the surface of the preloading

disk.

12. Assembly the upper part of the structure.

è do not correct the preload by turning the screw coun-

terclockwise!

è just start preloading again from 0kN!

è Use a new screw in case you exceeded its load limit.

Piezoelectric Force Sensors, Ring Force Transducers Measurement

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Fig. 20: Mounting in force shunt

Fig. 21: Mounting with preloading disk Type 9410A...

Fig. 22: Assembling with preloading disk Type 9410A...

5. Measurement

5.1 Basic arrangement of a measuring system

A measuring system is assembled from a quartz crys-

tal load washer, a highly-insulated low-noise connecting

cableandchargeamplier,adisplayand/ordataacquisi-

tion and processing unit.

Fig. 23: Measuringsystemconguration

Inthechargeampliertheelectricalchargegeneratedby

the sensor is converted into a proportional voltage, which

may be displayed, recorded or further processed. The

con-necting cable for the transducer must be highly insu-

latingand low-noise.The effectofthecable length(>15

m) can be obtained from the instruction manual for the

chargeamplieremployed.

Fromthechargeampliertothedisplayorrecorder,ordi-

nary coaxial cables may be used.

Piezoelectric Force Sensors, Ring Force Transducers Measurement

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5.2 Range selection and threshold

A distinction must be made between the measuring range

oftheloadwasherandthatofthechargeamplier.When

thecorrectpre-loadhasbeenapplied(chapter4.1.1,Fig.

3), the measuring range of the sensor can be chosen

freely, even down to 1% of the nominal force or less, with

roughly the same linearity. Of course, a calibration of the

corresponding range is recommended - on site or at Kist-

ler.

The measuring range desired for performing a measure-

ment can be selected freely on the charge amplier (for

example Kistler Type 5015A…). Charge amplier Type

5015A… provides continuous measuring setting ranges.

Together with load washers the following forces ranges in

Nresults:1…50,000N/Vor10Nto500kNfor10Vout-

put voltage. Of course the maximum admissible force for

the load washer in use must not be exceeded. For ranges

above50kNthereisthechargedivider10:1(forexamp-

leKistlerType5361).

It is for example possible to select a measuring range of

10Nandmeasuresmallforceuctuationssuperimposed

onastatic pretensionof,say,10kN.Briey overloading

small measuring ranges by a factor of 50 does not nor-

mallyharmthechargeamplier.Withbiggeroverloadsit

depends on the capacitance of the input cable whether

theamplierisdamagedornot.

Theinstructionmanualfortheparticularchargeamplier

used will provide information regarding is overload capa-

city.

For practical purposes at least, the threshold of a load

wash-ermayberegardedasinnitelylow.Togetherwith

a stand-ard charge amplier the practical limit is around

0,01N(signal-to-noiseratioabout50%).

5.3 Measuring high-frequency phenomena

Thanks to their high rigidity, quartz piezoelectric force

sensors are eminently suited for measuring rapidly chan-

ging processes. As the mounting situation has a decisi-

veeffect,thenaturalfrequenciesspeciedinthetableof

technical data are more of theoretical importance.

If a load washer is installed into a cylinder of the same

diameter for measuring axial force, it can be said without

contradiction that the dynamic properties of the measu-

ring object are not affected by installing the load washer.

There is no need whatever to take the natural frequency

of the load washer into consideration.

If on the other hand a large mass has to be supported

on three or four load washers, this assembly constitutes a

spring-mass oscillator. Obviously the natural frequency of

this system depends on the rigidity and not on the natural

frequency of the load washers and the magnitude of the

mounted mass. The natural frequency becomes higher as

theloadwashersusedbecomelarger(thatismorerigid).

The fact that the natural frequency of a larger load washer

is itself smaller is not important as far as the natural fre-

quency of the system is concerned. Thus dynamometers

with natural frequencies of several kHz can readily be ma-

nufactured.

Force links assembled from load washers Type 93x1C,

have natural frequencies from 22 to 85 kHz, depending on

size and weight.

5.4 Measuring quasistatic phenomena

Purely static measurements over any length of time are

not possible with the piezoelectric measuring principle.

The time interval during which so-called quasistatic meas-

urements can be performed depends on the insulation re-

sistance of the sensor and connecting cable on the pro-

pertiesofthechargeamplieremployed.

Withaninsulationresistanceof>1013 Wand<0.04 pC/s

amplier drift current, a time-dependent error of about

±0,5 N/min results using a load washer. Assuming a

measuring range of 5 000 N, this value implies an error of

0,1%(5N)ifthemeasurementlasts10minutes.

If the temperature of the transducer changes during the

measurement, a similar error signal must be expected;

this is often called the „temperature drift“. It is caused by

mechanical stresses acting on the quartz washers as a

Piezoelectric Force Sensors, Ring Force Transducers Calibration and maintenance

9001C_002-928e-12.20Page 36 Page 379001C_002-928e-12.20

result of thermal expansion. Changes in the temperature

in the structure in which the sensor is mounted also often

haveaneffect.Differentcoefcientsofthermalexpansion

can lead to deformation of the structure.

In principle a quartz load washer measures not the abso-

lute amount of a force but only changes of force. Normally

the force change is measured between the unloaded and

loaded states. With pretensioned force links the unloaded

statemaybedenedataneffectivepretensionofseveral

tons.

The quasi-static properties of a charge amplier are de-

scribed in the relevant instruction manual.

5.5 Instructions and safety precautions

Thesupportingsurfacesforaloadwashermustbe-

nelymachined(Ra=1.6),atandrigid

The maximum measuring range may be exploited only

if the force is distributed uniformly over the entire sup-

porting surface

With uneven surface loading, due to superimposed

exureforexample,themaximummeasuringrangeis

limited not by the range given in the table of techni-

caldatabutbythehighestlocalsurfacepressure(see

chapter4.2)

If a load washer is used to measure screw force, the

frictionsurface shouldbelubricated well(special gre-

ase Type 1063). With high surface pressure a thin

washer of beryllium copper will prevent pitting

To maintain the high insulation resistance the connec-

ting plug must be kept clean. The same applies to the

plug of the connecting cable. If necessary they should

becleanedwithFreonorrectiedbenzene.Ifthecable

is disconnected from the sensor, the protective cover

should be screwed on in its place

If trouble is encountered due to ground loops, the load

washer can be insulated from the object mass with so-

called insulating washers Type 95x7

6. Calibration and maintenance

6.1 In-Situ calibration of force sensors

Absolute measurement results can only be made if the

complete measurement assembly, e.g. the pretensioned

loadwasheranditsmounting xtures,hasbeencalibra-

ted.

If it is possible to remove the force measurement assem-

bly, without inuencing the pretension and load distribu-

ting of the force sensor, the assembly can be sent to a

Kistler Calibration Centre for recalibration. If, however, the

sensor is integrated into the machine structure, it normally

is not possible to remove the force measurement assem-

bly for recalibration. In this case an in-situ calibration must

be performed.

6.1.1 Working point calibration by peak value comparison

The test system is calibrated by comparing its output with

that of a reference measurement chain at loads around a

specicworkingpoint.Anaveragesensitivityiscalculated

from the peak values of both the reference and test sys-

tems recorded over multiple load cycles.

It is important to note the calculated sensitivity, S*, is valid

foraspecicmeasurementchain,i.e.sensor,chargeam-

pli-eranddisplayunit.Exchangingsensorsorampliers

will make the calibration invalid.

Furthermore, the sensitivity S* is calculated around a spe-

cic working point and will invariably differ slightly from

any works calibration results, which would have been de-

rived using a standard continuous calibration procedure.

It is generally also recommended to check the distribution

of the average sensitivity by calculating the standard devi-

ation of the sensitivity S*.

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Kistler 9041C Owner's manual

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Model: 9041C

Type: Owner's manual

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