Kistler 9371C Owner's manual

Instruction

Manual

Piezoelectric Load Cells

Type 9301C … 9371C

9301C_002-994e-09.21

Foreword

9301C_002-994e-09.21 Page 1

Foreword

Thank you for choosing a Kistler quality product

characterized 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

obligation 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

Holding AG and all its subsidiaries in Europe, Asia, the

Americas and Australia.

Kistler Group

Eulachstraße 22

8408 Winterthur

Switzerland

Tel. +41 52 224 11 11

[email protected]

www.kistler.com

Piezoelectric Load Cells, Type 9301C ... 9371C

Page 2 9301C_002-994e-09.21

Contents

1.Introduction .................................................................................................................................... 3

2.Important Notes ............................................................................................................................. 4

2.1For Your Safety .................................................................................................................... 4

2.2Notes on Handling the Instrument ....................................................................................... 5

2.3Tips on the Use of These Operating Instructions .................................................................. 6

2.4What Happens in the Event of Changes? ............................................................................. 6

2.5Disposal Instructions for Electrical and Electronic Equipment ................................................ 6

2.1Software Upgrades and Updates .......................................................................................... 6

3.General Description of the Instrument Text .................................................................................... 7

3.1What is the Purpose of a piezoelectric load cell? .................................................................. 7

3.2Functional Principle .............................................................................................................. 8

3.3Construction of the Piezoelectric Load Cell ........................................................................... 9

4.Assembly, Installation and Initial Start-up ..................................................................................... 10

4.1Important Notes ................................................................................................................. 10

4.2Installing the piezoelectric load cell ..................................................................................... 10

4.3Standard Wiring and Cabling of the Measuring System ..................................................... 13

4.4Various Mounting Possibilities, Force Introduction ............................................................. 15

5.Operation ..................................................................................................................................... 17

5.1Range Selection .................................................................................................................. 17

5.2Measuring Small Force Changes ......................................................................................... 17

5.3Useful Frequency Range ..................................................................................................... 19

5.4Temperature Influences ...................................................................................................... 20

5.5Polarity of the Measuring Signal ......................................................................................... 20

6.Maintenance ................................................................................................................................ 21

6.1Recalibrating the Instrument .............................................................................................. 21

6.2Maintenance Work ............................................................................................................ 21

7.Rectifying Faults ........................................................................................................................... 22

7.1Troubleshooting ................................................................................................................. 22

7.2Defective load cell .............................................................................................................. 23

8.Technical Data .............................................................................................................................. 24

9.Glossary ........................................................................................................................................ 25

9.1What does this Expression Mean? ...................................................................................... 25

9.2Measurement Uncertainty .................................................................................................. 29

9.3Linearity ............................................................................................................................. 30

9.4Frequency Range ............................................................................................................... 32

9.5Influence of Temperature ................................................................................................... 33

10.Warranty ...................................................................................................................................... 35

Total pages 35

Introduction

9301C_002-994e-09.21 Page 3

1. Introduction

Please take the time to thoroughly read this instruction

manual. It will help you with the installation, maintenance,

and use of this product.

To the extent permitted by law Kistler does not accept any

liability if this instruction manual is not followed or

products other than those listed under Accessories are

used.

Kistler offers a wide range of products for use in measuring

technology:

 Piezoelectric sensors for measuring force, torque, strain,

pressure, acceleration, shock, vibration and acoustic-

emission

 Strain gage sensor systems for measuring force and

torque

 Piezoresistive pressure sensors and transmitters

 Signal conditioners, indicators and calibrators

 Electronic control and monitoring systems as well as

software for specific measurement applications

 Data transmission modules (telemetry)

Kistler also develops and produces measuring solutions for

the application fields 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.

Piezoelectric Load Cells, Type 9301C ... 9371C

Page 4 9301C_002-994e-09.21

2. Important Notes

It is essential for you to study the following information,

compliance with which is for your personal safety during

the work and will ensure long, fault-free operation of the

instrument.

2.1 For Your Safety

 This instrument has been thoroughly tested and has left

the factory in a perfectly safe condition. In order to

maintain this condition and to ensure hazard-free

operation, the user must comply with the information

and warning notes contained in these operating

instructions

 The force transducer must be installed, operated and

maintained only by persons who are familiar with the

instrument and are adequately qualified for the work

concerned

 If safe operation is no longer assumed to be possible,

the instrument must be disconnected and made safe

against accidental operation

 It must be assumed that safe operation is no longer

possible

 when the instrument shows visible signs of

damage

 when the instrument is no longer operating

 after lengthy storage under unsuitable conditions

 after very rough transport conditions

Secure the load cell correctly. See details in section 4.2

Installing the piezoelectric load cell.

Secure all parts mounted on the load cell according to

the anticipated forces.

Important Notes

9301C_002-994e-09.21 Page 5

2.2 Notes on Handling the Instrument

 The load cell must only be used under specified

environmental and operating conditions

 The insulation resistance is of decisive importance in

piezoelectric sensors; it must be approximately 1014 Ω

(but at least 1013 Ω)

 In order to obtain this value, all plug connectors must

be kept scrupulously clean and dry

 The insulation resistance can be measured with the

insulation tester Type 5493

 Protect the instrument connector against contamination

and on no account touch it with your fingers (front of

connector). Fit the cover supplied when the connection

is not in use

 The connecting cable (from the force transducer to the

input of the charge amplifier) is highly insulated. Use

only the connecting cable specified

 The cable should not be removed from the force

transducer on any occasion after installation

 When it is not in use, protect the force link by storing it

in the packing case provided

 Ensure that the temperature of the load cell remains as

constant as possible during measurements, especially

when measuring quasistatically, i.e. in DC-mode (Long

Time Constant)

Piezoelectric Load Cells, Type 9301C ... 9371C

Page 6 9301C_002-994e-09.21

2.3 Tips on the Use of These Operating Instructions

We advise you basically to read through the entire

operating instructions. However, if you are in a hurry and

already have experience with Kistler piezoelectric load cells,

you can restrict yourself to the specific information needed.

We have endeavored to give these instructions a neat

layout to make it easy for you to gain direct access to the

information you require. Please keep these instructions in a

safe place where they are always to hand. If you lose these

instructions, please contact your Kistler customer service

organization and you will receive a replacement by return.

All details and directions in these instructions are subject to

change at any time without prior notice.

2.4 What Happens in the Event of Changes?

Equipment modifications will normally result in changes to

the operating instructions. In such cases, please contact

your Kistler customer service organization concerning

updating facilities for your documentation.

2.5 Disposal Instructions for Electrical and Electronic Equipment

Do not discard old electronic instruments in municipal

trash. For disposal at end of life, please return this product

to an authorized local electronic waste disposal service or

contact the nearest Kistler Instrument sales office for

return instructions.

2.1 Software Upgrades and Updates

Kistler may from time to time supply upgrades or updates

for embedded software. Such upgrades or updates must

always be installed.

Kistler declines any liability whatsoever for any direct or

consequential damage caused by products running on

embedded software which has not been upgraded or

updated with the latest software supplied.

General Descripti

9301C_002-994e-09.21 Page 7

3. General Description of the Instrument Text

3.1 What is the Purpose of a piezoelectric load cell?

The piezoelectric load cell is used to measure dynamic or

quasi-static tractive forces and pressures. The force trans-

ducer is characterized by high rigidity and thus has a high

natural frequency. Its high resolution makes it possible to

measure minute dynamic changes in large forces. The

useful frequency range depends mainly on the natural

frequency of the entire measuring system.

Fig. 1:Piezoelectric load cells, Type series 93x1C

The most important fields of application for the force

transducers are:

Calibration processes

Automobile industry

 Safety engineering, monitoring of impact forces

 Shock forces in chassis

 Forces in balancing machines

Material testing

 Impact testing, fatigue strength cycling

Piezoelectric Load Cells, Type 9301C ... 9371C

Seite 8 9301C_002-994e-09.21

Machine tools

 Monitoring of presses, stamping

 embossing and welding machinery

 Force measurements at longitudinal guides

General machine building

 Monitoring of supporting forces (oscillating forces) on

machinery, mounted on damping elements

 Chucking processes e.g. load cell combined with

hydraulic cylinder

 Jointing technique (insertion, force-fitting of compo-

nents)

Quality control

 Force measurements on switches

3.2 Functional Principle

The force to be measured is introduced via the nut to the

mechanically preloaded load washer.

The load washer contains a pair of quartz crystal plates

sensitive to pressure. Measurement takes place practically

without displacement.

Fig. 2: Sectional view of a quartz load washer

Positive or negative charges appear at the connection

depending on the direction of the force.

A negative charge produces a positive voltage at the

output of the charge amplifier and vice versa.

General Description of the Instrument Text

9301C_002-994e-09.21 Seite 9

3.3 Construction of the Piezoelectric Load Cell

The load cell consists of a load washer mounted under high

preload between a preloading bolt and a nut.

This preload is necessary for measurement of the tractive

forces.

1. Load washer

2. Connector

3. Nut

4. Ground-isolation

5. Centering seat

6. Mounting thread

7. Preload screw

Fig. 3: Construction of the force transducer

The load washer is ground insulated. This largely excludes

ground loop problems.

The force transducer is corrosion resistant, the sensor is

lightwelded and the connector is protected against the

ingress of spray water. (Requirement: correctly mounted

O-ring in the cable connector).

The turned seat can be used for accurate centering of the

load cell.

Piezoelectric Load Cells, Type 9301C ... 9371C

Seite 10 9301C_002-994e-09.21

4. Assembly, Installation and Initial Start-up

4.1 Important Notes

Piezoelectric load cells of Types 9301C ... 9371C are

precision instruments which must be carefully handled if

their inherent accuracy is to be maintained in a useful state.

You should therefore comply with the following notes:

 Do not allow the force transducer to be dropped and

do not expose it to hard impacts! The highest force

from such shocks could exceed the measuring range of

the load cell.

 Do not use a hammer to position the workpieces, as

hammer blows can also cause damage!

The following sections contain notes on the installation of

piezoelectric load cells and construction of the measuring

chain.

4.2 Installing the piezoelectric load cell

Correct installation of the load cell requires

compliance with the following notes:

 The load cell should only be installed by persons who

are familiar with the instrument and are adequately

qualified for this work

 Before installing the force transducer, check the flatness

of the contact surfaces, which should be flawlessly

machined with a surface roughness of Ra (≤6,3 μm /

≤N9). Thoroughly clean the contact surfaces before

installation. Uneven contact surfaces will cause

eccentric application of force. With high forces, this

could lead to overloading of the sensor element

 Connect the connecting cable only after completing

installation of the force transducer. Always leave the

plastic cover screwed on during installation work. Great

care should be taken in heavily contaminated

environments

Any contamination of the plug connections at the sensor or

cable end can cause considerable measuring errors (above

all drift)

Assembly, Installation and Initial Start-up

9301C_002-994e-09.21 Seite 11

Fig. 4: Fitting load cells

 A load cells is fitted using fittings with appropriate outer

threads or screws. When firmly tightening a screw

connection, ensure when holding the force transducer

that the hexagon wrench is always applied close to the

fastening side. If it is applied wrongly to the opposite

side, there is the danger that the preloaded load cell

itself will become dismantled and thus rendered

unusable for all practical purposes! The load cell would

then have to be preloaded again and calibrated!

 S = clearance between the force transducer and the end

of the thread of the fastening-part screw / fastening

part. During the installation procedure, ensure that

there is always a minimum distance S of approx. 0,5

mm or half a screw turn as clearance

 The connecting cable can now be connected to the load

cell. Clean both sides of the connector (load cell and

cable) with the cleaning and insulation spray Type 1003

 The O-ring provided is used for sealing. The contact

surfaces for the O-ring must be clean. Insert the O-ring

and screw the cable on firmly

Fig. 5: Installing the force link

Piezoelectric Load Cells, Type 9301C ... 9371C

Seite 12 9301C_002-994e-09.21

Fig. 6: Installation example of a force transducer

 Wherever possible, keep the connecting cable

permanently connected to the load cell

 Install the connecting cable so that it cannot shear off

or be ripped out under working conditions

Assembly, Installation and Initial Start-up

9301C_002-994e-09.21 Seite 13

4.3 Standard Wiring and Cabling of the Measuring System

The electrical charges (pC) yielded by the sensor element

are converted by charge amplifiers into proportional

voltages which can be indicated, recorded or further

processed by standard instruments.

Compliance is required with the following notes when

connecting cables to the measuring system:

 The connecting cables from the load cell to the charge

amplifier must be highly insulating and be low noise.

For these reasons, use only the connecting cables

specified

 Standard cables can be used for connections between

the charge amplifiers and the indicating or analyzing

instruments

 In all work involving electrical connections, proceed

carefully and maintain cleanliness. Remove cover caps

from connectors only immediately before connecting a

cable

 By connecting sensors in parallel, a summation of the

charge and thus of the forces can be obtained. Only

one charge amplifier is needed

Piezoelectric Load Cells, Type 9301C ... 9371C

Seite 14 9301C_002-994e-09.21

The following drawing shows the elements required for

connecting a load cell to a charge amplifier.

Fig. 7: Connecting a load cell to a charge amplifier

Cable Type 1631C... is available in various lengths. Types

1603B... can be used as extension cables.

Assembly, Installation and Initial Start-up

9301C_002-994e-09.21 Seite 15

4.4 Various Mounting Possibilities, Force Introduction

Fig. 8: Mounting examples; various types of force

Introduction

The piezoelectric load cell can measure tensile and

compressive forces in the longitudinal axis of the element.

Bending moments, torsional moments as well as shear

forces should be avoided as far as possible. Up to a certain

degree, such forces deviating from the main force direction

can be tolerated by the force transducer.

S = Clearance Between load cell and end of thread of the

fastening screw / fastening part.

Fs = Side force [N] This so-called disturbing force

introduces certain shear forces and bending moments to

the load cell. The maximum tolerable values are listed in

section 8.1 Technical Data.

Piezoelectric Load Cells, Type 9301C ... 9371C

Seite 16 9301C_002-994e-09.21

Fig. 9: Mounting examples of a load cell in a hydraulic

chucking device. Monitoring of tensile and compressive

forces

Fig. 10: Mounting with force distributing cap Type

9500A... and flange Type 9501A...

Operation

9301C_002-994e-09.21 Seite 17

5. Operation

5.1 Range Selection

It is advisable to use charge amplifiers with sensitivity

adjustment with load cells Type 9301C ... 9371C. Set the

sensitivity according to the data in the calibration

certificate. The output voltage is then adjusted directly to

the value corresponding to the scale selected (...N/V). To

set the sensitivity, consult the operating instructions for the

charge amplifier.

5.2 Measuring Small Force Changes

The piezoelectric method of measurement allows very

accurate measurement of small force changes when there

is a large preload present at the same time. When, for

example, fluctuations Fz of about 10 N are superimposed

on a main force Fz of about 20 kN, the following rules can

be applied:

Fig. 11: Force measurement with preload

Piezoelectric Load Cells, Type 9301C ... 9371C

Seite 18 9301C_002-994e-09.21

a Set the amplifier to Reset. Select the range for F as

follows: 2 • 103 N/V (amplifier to Long Time Constant)

b Switch the amplifier to Operate

c Introduce force Fz (Start machine tool)

d After reading and/or recording the force, switch the

amplifier back to Reset to dissipate the charge

corresponding to Fz

e Switch the amplifier to a more sensitive range (e.g. 1

N/V for Fz)

f Set the amplifier to Short Time Constant

g Switch the amplifier to Operate. The Fz variations can

now be measured with great accuracy, since the

dynamic response threshold is around 0,02 N. This

means that a Fz of 0,02 N (as a change of Fz ≈20 kN)

will produce an output voltage of approx. 20 mV

The resolution which can be achieved is thus:

1

––––––––– !

1 000 000

h Switch the amplifier to Reset

i Switch the amplifier back to a less sensitive range

(2 • 103 N/V). Select Long Time Constant and switch

the amplifier to Operate

j The disappearance of Fz can also be recorded

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