Kistler 9212 Owner's manual

Brand: Kistler

Model: 9212

Type: Owner's manual

Instruction

manual

Load cells -

high impedance,

charge mode

Type 9212

9212_002-721e-07.22

Foreword

9212_002-721e-07.22

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 to the content without obligation to notify any

person or organization of such changes or improvements.

pressly provided herein, no part of this manual may be repro-

duced for any purpose without the express prior written consent

of Kistler Group.

Kistler Group

Eulachstrasse 22

8408 Winterthur

Switzerland

Tel. +41 52 224 11 11

info@kistler.com

www.kistler.com

Page 1

9212_002-721e-07.22Page 2

Load cells - high impedance, charge mode

Content

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

2. Important information ......................................................................................................................5

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

2.2 Precautions ............................................................................................................................6

2.3 Disposal of electronic equipment ...........................................................................................6

2.4 Product Types ........................................................................................................................7

2.5 Nomenclature .........................................................................................................................7

3. Product description ..........................................................................................................................8

3.1 Supplied mounting studs ........................................................................................................8

4. Technical information, functional description ...............................................................................9

4.1 Piezoelectric measurement concept ......................................................................................9

4.2 High impedance output ..........................................................................................................9

5. Mounting and installation ..............................................................................................................10

5.1 General.................................................................................................................................10

5.2 Surface preparation ..............................................................................................................10

5.3 Mounting...............................................................................................................................10

6. Operation.........................................................................................................................................12

6.1 Charge mode load cells and charge ampliers ....................................................................12

6.1.1 The charge amplier ...............................................................................................12

6.1.2 Charge amplier operation .....................................................................................13

6.1.3 Kistler charge ampliers .........................................................................................15

6.1.4 Cable considerations ..............................................................................................15

6.1.5 Drift due to the charge amplier ..............................................................................17

6.1.6 Load cell start-up with charge amplier ..................................................................19

7. Calibration and maintenance ........................................................................................................20

7.1 General.................................................................................................................................20

7.2 Troubleshooting ....................................................................................................................20

7.3 Repairs .................................................................................................................................20

7.4 Care and cleaning ................................................................................................................21

7.5 Calibration ............................................................................................................................21

Page 39212_002-721e-07.22

Content

Total pages: 25

8. Recommended cables....................................................................................................................22

9. Storage and transit considerations ..............................................................................................23

10. Warranty ........................................................................................................................................24

11. Appendix .......................................................................................................................................25

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Load cells - high impedance, charge mode

Page 4

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.

These instructions describe Kistler Type 9212 high impedan-

ce, charge mode load cells.

Performance features at a glance:

High impedance, charge mode

Rugged quartz force-sensing element guarantees long-

term stability

Wide measuring ranges for compression and tension

Quasi-static response

High operating temperature range: –240 ... 150 °C

[–400 ... 300 °F]

Kistler oers 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 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, in addition to our

detailed data sheets, will provide you with an overview of our

product range. All unit measurements provided are listed in

order of meters, followed by inches [in brackets].

If you require additional assistance beyond what can be loca-

ted online or in this manual, please contact Kistler‘s extensive

support organization or visit us online at www.kistler.com.

1. Introduction

9212_002-721e-07.22

Important information

Page 5

2. Important information

Compliance with local safety regulations, which may apply to

the use of power line operated electrical and electronic equip-

ment, is strongly recommended.

It is essential for you to review the following information,

which is intended to ensure your personal safety when

working with the load cells and contribute toward a long-fault-

free service life.

2.1 For your safety

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Load cells - high impedance, charge mode

Page 6

2.3 Disposal of electronic equipment

2.2 Precautions

Compliance with the following precautionary measures is

vital to ensure safe and reliable operation:

Check all equipment packaging for transporation damage.

Report any damage to the transporter and to Kistler.

The equipment should be used only under the specied ope-

rating conditions and must be protected against excessive

dust and mechanical stress (shock, vibration, etc.).

Avoid high atmospheric humidity, which can lead to conden-

sation during changes in temperature.

If there is evidence that safe operation is no longer possib-

le, the instrument must be powered o and rendered safe

against accidental start-up. Safe operation is no longer pos-

sible when the product

▪ shows visible signs of damage

▪ is no longer operating

▪ has been subjected to prolonged storage under unsuitable

conditions

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 oce for disposal instructions.

9212_002-721e-07.22

Important information

Page 7

2.4 Product Types

This instruction manual summarizes Kistler Type 9212 high

impedance, charge mode load cells. Please reference the

corresponding data sheets for each type for more detailed

specications.

Series Type 9212

Fig. 1: Series Type 9212 load cell appearance

2.5 Nomenclature

Table 1: Manual nomenclature

Throughout this manual, special designations and

nomenclature are used for terms and concepts relating to

load cells. These are identied in Table 1.

Term Definition

Fs Full-scale

pC picoCoulomb, a unit of electrical charge equivalent to

1 X 10-12 Coulomb

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Load cells - high impedance, charge mode

Page 8

3. Product description

Kistler load cells are compact, sensitive and fast response

sensors for measuring dynamic and short-term static forces.

Both compression and tension forces can be measured.

Typical applications include measuring fatigue-test tension,

rocket engine thrust, clamping force and forces transmitted

by vibration exciters. In simple terms, this unit could also be

described as a force probe.

These load cells are designed for bottom surface mounting

with an upper force application surface. The units dier in

conguration by the location of the cable connector. Series

Type 9212 feature the connector positioned radially. This

latter conguration, along with a low threshold and 2 260 kg

[5 000 lb] measuring range, simplies widely conducted drop-

testing by measuring forces instead of shock levels.

A self-generating piezoelectric sensing element is used

internally to produce a charge output. As with most high

impedance, charge mode sensors, the sensitivity of these

load cells is expressed in terms of the ratio of the electrical

output to applied force (i.e. –pC/lbf or –pC/N).

Being a high impedance device, a charge amplier and low

noise cabling are required.

Charge ampliers are available in several forms. Desktop

and rack mount units usually oer extensive operator

convenience for range selection, dierent time constants

and signal ltering. Miniature in-line versions in single and

multiple channels are useful where load cells are remotely

located or in industrial environments. While the use with

Kistler charge ampliers is always preferred, other models

can be used. A typical measuring system is shown in Section

4.2, while a summary of Kistler charge ampliers is included

in Section 6.1.3.

3.1 Supplied mounting studs

The following supplied mounting studs are listed in Table 2.

Load Cell

Type No.

Item Description Qty. Kistler

Part No.

9212 Mounting stud, threading –

10-32 to 10-32 2 8402

Table 2: Supplied mounting studs

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Technical information, functional description

Page 9

4. Technical information, functional description

Piezoelectric load cells convert force into an electric charge.

The charge derived by the load cell is proportional to the

force acting on the internal piezoelectric element. The

element consists of precision-cut quartz. Quartz has been

used by Kistler in instrumentation since 1954 and continues

to be the ideal choice for load cells. Like other piezoelectric

materials, quartz when subjected to a force, generates a tiny

charge. This type of element is quite unlike a strain gage

sensor, which is passive and requires a source of excitation

to function. Thus, this type of load cell is said to be active or

self-generating.

4.1 Piezoelectric measurement concept

High impedance load cells require an external charge

amplier (item 3 in Fig. 2). A low noise cable must be used

between the sensor and charge amplier (item 2 in Fig. 2).

4.2 High impedance output

Fig. 2: Diagram of a high impedance load cell system

Item 1 High impedance sensor (pC/lb or pC/N)

Item 2 Low noise coaxial cable

Item 3 Charge amplier

Item 4 Output cable

Item 5 Read-out or analysis equipment

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Load cells - high impedance, charge mode

Page 10

5. Mounting and installation

5.1 General

For proper operation of load cells, care must be taken during

the installation process. Careful installation will result in opti-

mal accuracy and reliability.

5.2 Surface preparation

Surfaces on or between which a load cell is mounted must

be at. Ground or lapped mounting surfaces are desirable.

For maximum accuracy and frequency response, the rough-

ness should not exceed 4.06 X 10-4 mm [16 μin] and atness

should be 25.4 X 10-4 mm [0.0001 in]. Severe uneveness

can cause stress concentration leading to sensing element

damage.

If the load cell is to be placed between two surfaces, the two

surfaces must be parallel at all times and should not impart

more than 45 kg [100 lb] transverse load.

5.3 Mounting

Load cells are mounted with supplied studs, either one or two

depending on the type. The stud requires a mounting surfa-

ce hole tapped with a 10-32 thread for Type 9212. The hole

depth must be such that the stud will not bottom out. Table 3

indicates the Kistler order number for studs. These studs are

machined from Beryllium Copper for high strength and low

modulus of elasticity, coupled with high elastic limits. Substi-

tutions should be carefully evaluated before use.

The following stud installation guidelines should be followed:

1. Drill and tap an adequate hole to ensure a ush mount of

the load cell. Make sure the stud does not bottom out. A

chamfer should be machined at the top of the mounting

hole to ensure that the base of the load cell makes full

contact with the mounting surface.

2. Completely clean the surface prior to mounting.

3. Apply a thin coat of silicon grease to both the load cell

and mounting surface.

9212_002-721e-07.22

Mounting and installation

Page 11

4. Always use the proper sockets and a torque wrench

when installing load cells. Tighten to the torque specied

on the individually supplied calibration certicate or as

specied in Table 3. DO NOT OVER TIGHTEN.

Load Cell Type Upper/lower studs N·min-lb

9212 yes/yes 2.25/2.7 20/24

Table 3: Recommended mounting torque

The load cell may be mounted in any attitude, and generally

without regard for top or bottom orientation. Top and bottom

surfaces are indicated by the appearances of the upper and

lower mounting surfaces (bosses). The load cell Series Type

9212 top has a single ring and the bottom has two annular

rings.

It is perfectly acceptable to use a single mounting stud with

Series Type 9212. When working with very small forces, a

single stud is recommended. With small forces the mass of

the outer body and base could interfere, aecting frequen-

cy response or masking the results of impact tests. In such

cases, mount the load cell on its bottom only and apply the

force to the top.

For compression force measurement alone, the installation

can be simplied by eliminating one of the mounting studs.

Both the mounting surface and the surface that bears the

load cell must remain at and parallel.

Care should be taken in any installation to ensure that the

cable is not stressed, kinked or otherwise damaged. The

coaxial cable furnished is a special low noise variety, not to

be confused with ordinary coax cables. A very high insulation

resistance must be maintained within the circuit from the load

cell to the charge amplier. Anything that will jeopardize the

transfer of the load cell output charge to the charge amplier

will degrade load cell performance.

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Load cells - high impedance, charge mode

Page 12

Load cells use piezoelectric, self-generating materials. The

quartz plates that make up the sensing elements produce an

electrical charge when stressed by the force being measured.

Piezoelectric load cells are a well established class of sensors

and are made in high impedance, charge mode styles and

low impedance, voltage mode types. These load cells are in

the charge mode family of sensors. Charge mode sensors

do not require any power supply to operate. Voltage mode

sensors contain internal electronics in addition to the sensing

element that does require a power source.

This section covers the interface, signal conditioning,

frequency response inuences and cable considerations.

6. Operation

The key characteristic of charge mode operation is the very

high impedance requirement. From the charge output of the

load cell, through the cable and to the charge amplier input

connector, the high insulation level must be maintained. If the

insulation resistance is compromised, excessive zero-drift

may occur.

Charge ampliers complement the load cell, aording a high

degree of exibility. Kistler's versatile laboratory charge ampli-

ers have sensitivity adjustment and multi-ranging capability.

6.1 Charge mode load cells and charge ampliers

6.1.1 The charge amplier

Since load cells exhibit a high impedance output in the

range of 10^13 ... 10^14 Ohm, an amplier with a high input

impedance is required. High impedance voltage ampliers

were once used but, since the introduction of the charge

amplier by Kistler, voltage ampliers are seldom used

anymore in piezoelectric applications.

Charge ampliers are associated with high impedance,

charge mode sensors. Charge ampliers should not be

confused with couplers which power and amplify signals from

low impedance, voltage mode sensors. There is also a class

of electronic units called dual mode ampliers. These are

combination units that accept both charge mode and voltage

mode sensors.

9212_002-721e-07.22

Operation

Page 13

6.1.2 Charge amplier operation

The charge amplier consists of a high-gain inverting voltage

amplier with a MOSFET or JFET at the input to achieve high

insulation resistance. As the load cell, input cable and charge

amplier are interconnected and the individual components

blend to form a single circuit.

Charge ampliers are designed in several variations to

accomplish the measurement task in the most cost-eective

manner. Charge ampliers dedicated to a particular applica-

tion often do not require user adjustment and take the form of

a sub-assembly. Such units are inline connected and may be

single or multiple channel depending on system complexity.

In contrast, a load cell used for research and development

purposes will require a full featured charge amplier for exi-

bility and convenience. Some features, such as adjustable

scaling, contribute to making the load cell more useful and

adaptable while others, such as ltering, improve the useful-

ness of the data. In any measurement situation, the charge

amplier selected should be based on the application and

load cell requirements.

Fig. 3: Circuit of a charge amplier and load cell

Location Description

CtLoad cell capacitance

CcCable capacitance

CrRange Capacitor

Range capacitor insulation – this value varies by switching

from short (109Ω), medium (1011Ω), to long (1013Ω)

RiInsulation resistance

q Charge from load cell

VoOutput voltage

A Open-loop gain

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Load cells - high impedance, charge mode

Page 14

A simplied equivalent diagram of the accelerometer, input

cable and charge amplier is shown in Fig. 3.

Two circuit features of the charge amplier play key roles. Cr

is a range capacitor bridging the amplier input and output.

Rt is the insulation resistance of that capacitor. This value is

range switch selectable as indicated in Fig. 3.

Neglecting resistance momentarily, the level of output voltage

Vo is equal to the amount of charge produced by the load cell

divided by the capacitance of the feedback or range capacitor

Cr.

In actual operation, the range capacitor value in Fig. 3 is

adjusted by a charge amplier control labeled as range. For

the remainder of this discussion, the capacitor will be called

the "range capacitor."

The charge amplier essentially acts as a charge integrator,

which compensates the load cell’s charge with a charge of

equal magnitude and opposite polarity in order to ultimately

produce a voltage across the range capacitor. Resultingly,

a high impedance charge is converted to a low impedance

voltage.

As stated above, the charge integration process is aected

with a charge of the same magnitude and opposite polarity.

Thus, a negative charge at the amplier’s input is converted

to a positive output voltage. This is why charge mode sensors

are typically indicated with a negative output.

For simplicity sake, the resistive eects have not been consi-

dered. As shown in Fig. 3, the familiar capacitive-resistive

network is bridging the amplier input to the output. Due to

this network, a time constant is introduced into the discharge

rate of the range capacitor. Time constant is dened as the

discharge time of an AC coupled circuit. In a period of time

equivalent to one time constant, a step input will decay to

37 % of its original value. Therefore, the time constant (TC)

of a charge amplier is simply:

TC = Rt CT

The rst of two undesirable inuences on charge ampli-

er output is this time constant capacitor discharge rate.

The second inuence is drift. Drift, as dened here, is the

undesirable change in output signal level over time which

is not a function of the measured variable. Drift in a charge

amplier is caused by a low insulation resistance Ri at the

input or by internal leakage current of the input MOSFET or

JFET.

9212_002-721e-07.22

Operation

Page 15

Very practical measuring consequences are associated with

the duration of time constants. The longer the time constant,

the better the low frequency response and the longer the

useable measuring time.

As the operation of the load cell is closely associated with

the charge amplier, proper selection of a charge amplier is

essential. While it is always preferable to use a Kistler charge

amplier, other units may not operate with the load cell satis-

factorily.

6.1.3 Kistler charge ampliers

Kistler oers a comprehensive line of charge ampliers. If

the user is utilizing these instruments, they are designed for

compatibility with all load cell charge mode accelerometers.

The chart below provides a listing of available charge ampli-

ers. Please request data sheets on specic models.

Type Description

5010

This series of bench type single channel charge ampliers is the most versatile of the

Kistler line as it is dual mode and can accept low impedance, voltage mode sensors as well.

Push-button, keypad controls for sensitivity, range, operate/reset, time constant and select-

able ltering; also rack mountable.

5015 Universal single-channel charge amplifier with charge input, Piezotron input (option) and

remote control via RS-232C or IEEE-488.

5018 Universal analog charge amplifier, optional Piezotron input; RS-232C & USB interface;

extremely wide charge and frequency range; outstanding noise performance.

5039 This series of small single and dual range charge amplifiers is furnished with BNC/TNC con-

nectors in a choice of ranges. Enclosures are shock resistant and rated to NEMA 4X.

6.1.4 Cable considerations

As has been noted in the charge amplier discussion, the

lowering of the insulation resistance of the input circuit Ri,

indicated in Fig. 3, seriously compromises the operation of

the load cell to measure short term quasistatic events. The

main functions of the input cable are to connect the load cell

output to the charge amplier, without leakage, attenuation

or pickup of interference.

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Load cells - high impedance, charge mode

Page 16

The relatively low signal and the need to maintain an ultra-

high insulation level combine to require a care level above

what is normal for low impedance, voltage mode measu-

ring systems. Maintaining the insulation level requires that

ordinary human body oils and moisture do not touch most

areas of the load cell cable connector. A high cleanliness

level is needed to keep connector surfaces absolutely clean.

The consequence of a lower than 10^12 Ohms insulation

level is a loss of output so great that measuring may not be

possible. A low insulation value could lead the user to believe

the load cell is not functioning properly.

Low noise cables should always be used when using charge-

mode. It is important that these cables be secured from

movement during operation. Cable movement can generate

triboelectric noise causing possible measurement errors.

When using load cells, the user should observe the following

precautions.

Compliance with the following precautionary measures is

vital to ensure safe and reliable operation:

▪ Make certain the uoropolymer insulator of all input

plugs are clean and not touched with the ngers. Al-

ways keep the BNC connectors clean and dry. Clean with

approved cleaners or a spray-on contact cleaner using a

paper tissue that does not shed bers.

▪ Short cables prior to connection to the input of the

charge amplier. A charge can be present on the cable's

end with sucient energy to cause damage to the input

FET amplier.

▪ Short the unit into the reset mode when connecting

the load cell to the charge amplier. Failure to do so

may result in damage to the input circuit.

▪ Connect cabling from the output BNC connector to the

appropriate read-out or recording instrumentation as

required.

9212_002-721e-07.22

Operation

Page 17

Fig. 4: Drift of the charge amplier

6.1.5 Drift due to the charge amplier

Any drift detectable at the output of the charge amplier may

be due to one (or more) of the following causes (see Fig. 4).

Cause 1 Drift due to insucient insulation resistance in

the internal charge amplier feedback loop.

Cause 2 Drift due to damaged or defective MOSFET in

input stage (positive or negative going).

Cause 3 Drift due to low insulation resistance at the input

of charge amplier.

9212_002-721e-07.22

Load cells - high impedance, charge mode

Page 18

Remedies for Fig. 4 can be obtained by trying the following

measures:

Cause 1

Distinctive sign: Exponential decreasing of the signal.

• Set the [Time Constant] to 'Long' since the [Medium] and

[Short] settings show the same drift as a low insulation

resistance in the feedback loop.

• If the trouble persists, a low insulation resistance in the

selected range capacitor is the cause.

Cause 2

Distinctive sign: Polarity of the drift does not depend on

the polarity of the zero oset at the input.

A small drift, as specied in the technical data, is normal and

given by the very nature of the charge amplier.

Cause 3

Distinctive sign: Polarity of the signal depends on the

polarity of the zero oset at the input.

Most probable cause is a low insulation resistance in the load

cell circuit. A check may be performed with the Type 5493

insulation tester.

• Clean load cell plug or replace load cell; clean load cell

cable (cable connections) or replace it.

Cause 3 is easily diagnosed by disconnecting the load cell

and its cable from the charge amplier and connecting a

charge calibrator. It may also be a result of low insulation re-

sistance of the input circuitry, which will require servicing.

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Kistler 9212 Owner's manual

Brand: Kistler

Model: 9212

Type: Owner's manual

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Kistler 9212 Owner's manual

Kistler 9212 Owner's manual

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