Kistler 8742A Series User manual

002-096e-01.19
Instruction
Manual
Shock Accelerometers
Type 8742A…
ä

Shock Accelerometer Page 1
002-096e-01.19
Instruction
Manual
Shock Accelerometers
Type 8742A…
CE
Kistler Instrument , 75 John Glenn Drive , Amherst, NY 14228-2171, Tel: [phone]

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Table of Contents
1Introduction ...................................................................................................................................... 3
2Important Guidelines ........................................................................................................................ 3
2.1 For your safety..................................................................................................................... 3
2.2 Precautions .......................................................................................................................... 4
2.3 Using This Manual ............................................................................................................... 4
2.4 Shock Accelerometer Types.................................................................................................. 5
2.5 Manual Nomenclature ......................................................................................................... 5
3General Description .......................................................................................................................... 5
4Technical Information, Functional Description .................................................................................. 6
4.1 Piezoelectric Measurement Concept..................................................................................... 6
4.2 Shear Element Background................................................................................................... 6
4.3 Low Impedance Output ....................................................................................................... 6
5Installation ........................................................................................................................................ 7
5.1 General ................................................................................................................................ 7
5.2 Surface Preparation.............................................................................................................. 7
5.3 Stud Mounting..................................................................................................................... 8
5.4 Securing Cables.................................................................................................................... 9
6Operation........................................................................................................................................ 10
6.1 Powering ........................................................................................................................... 10
6.1.1 Using “Built In” Power Sources.......................................................................................... 10
6.1.2 Kistler Couplers .................................................................................................................. 11
6.1.3 The Constant Current Power Supply/Coupler .................................................................... 11
6.1.4 Sensor Power-Up ............................................................................................................... 14
6.1.5 Overload Recovery ............................................................................................................ 14
6.1.6 Supply Voltage Effects ....................................................................................................... 14
6.2 Driving Long Cables........................................................................................................... 15
6.3 Frequency Response Limits ................................................................................................ 17
6.3.1 Definition and Frequency Response Standards ................................................................... 17
6.3.2 High Frequency Limitations................................................................................................ 17
6.3.3 Low Frequency Limitations - Transducer ............................................................................ 19
6.3.4 Low Frequency Limitations - Coupler and Readout Instrumentation................................... 21
7Maintenance and Calibration .......................................................................................................... 22
7.1 General .............................................................................................................................. 22
7.2 Trouble Shooting ............................................................................................................... 22
7.3 Repairs............................................................................................................................... 23
7.4 Cleaning ............................................................................................................................ 23
7.5 Calibration ......................................................................................................................... 23
8Accessories ..................................................................................................................................... 24
8.1 Cables................................................................................................................................ 24
9Warranty ......................................................................................................................................... 24

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1Foreword
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.
© 2006 … 2019 Kistler Group. Kistler Group products are protected 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.
2Introduction
By choosing Kistler shock accelerometers you have opted for an
instrument distinguished by precision, long life and technical
innovation. Please read these instructions carefully before installing
and operating these instruments.
Kistler offers a wide selection of measuring instruments and
comprehensive systems including:
* Sensors for force, pressure, acceleration, shock, vibration and strain.
* Associated signal conditioners and accessories.
* Piezoresistive pressure transducers and transmitters with associated
amplifiers.
Kistler can also provide entire systems for special purposes in the
automotive industry, plastics processing, and biomechanics. Our
general catalog provides information on Kistler products and services.
Detailed technical data sheets are available on most products offered.
Worldwide customer service is at your disposal should you have any
questions regarding this or other Kistler products. Information on
your specific application is also available from Kistler.
3Important Guidelines
To ensure your personal safety, please observe the safety guidelines in
this section.
3.1 For your safety
* Carefully follow the installation information contained in section
5 of this manual.

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* Do not drop the instrument.
* Store in the case provided and in a clean, dry environment.
* Power the instrument in accordance with the instructions in
section 6 of this manual.
3.2 Precautions
Kistler sensors are thoroughly tested before leaving the factory. To
maintain safe and reliable operation, it is important to follow the
instructions herein.
* Do not mount accelerometers on high voltage surfaces.
* Keep cable clear of power lines and open machinery.
* Never operate or store the unit beyond the specified temperature
range.
* Do not exceed the maximum specified current.
* Never exceed the maximum specified voltage.
* Follow the instructions for mounting. Do not over tighten.
* When not in use, store the accelerometer in the container supplied.
Always store in a clean, dry area.
* Keep the connector clean and covered when not in use
•Exercise care during cable connection. Cable connector center pin
should align with the female receptacle on the accelerometer.
* Follow the recommendations in section 7.4
3.3 Using This Manual
Information contained herein includes a technical description,
installation and operating instructions, powering and considerations
for cable length. Section 8 contains a listing of mounting accessories
and cables available to assist with your measurement needs.
It is recommended that the entire manual be read prior to installation
and operation of shock accelerometers. The user who has prior
experience with Piezotron type accelerometers may want to confine
reading to particular sections of interest.
We have endeavored to arrange these instructions in a manner that
allows for easy location of topics of interest. Your Kistler
representative is also available to assist with any questions.
Information contained herein may be subject to change.

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3.4 Shock Accelerometer Types
This manual is applicable to all shock accelerometers listed on the title
page. Please see the product data sheets at the rear of this manual for
detailed specifications.
Figure 1: 8742A and 8741A…M1… Shock Accelerometer
3.5 Manual Nomenclature
Throughout this manual some special designations and nomenclature
are used for specific terms and concepts relating to shock sensors.
These are explained in Table 1.
Term: FS
Definition: Full Scale
Table 1: Manual Nomenclature
4General Description
Kistler shock accelerometers are shear mode shock and vibration
measuring instruments. These units are intended for pyroshock
testing, metal-to-metal impact studies, drop testing, etc. A self-
generating piezoelectric sensing element is used in conjunction with
the built-in, internal circuit Piezotron* impedance converter. As with
most accelerometers, the sensitivity of this series is expressed in terms
of the ratio of the electrical output to applied acceleration (e.g.
mV/g). In the case of Piezotron devices such as used in this
accelerometer, the output is a low impedance voltage signal which is
proportional to the applied acceleration.
Being a low impedance device, no charge amplifier or special cabling is
required and transmission over long lines is possible with a minimum
of noise pick-up.

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5Technical Information, Functional Description
5.1 Piezoelectric Measurement Concept
Piezoelectric accelerometers convert acceleration into an electric
charge. The charge derived by the accelerometer is proportional to
the force acting on the internal quartz (piezoelectric) element.
Accordingly, the mechanical variable (acceleration) is derived from a
force measurement. Shock accelerometers are specially tailored to
measure high acceleration from pyro shock levels to impact test
information.
5.2 Shear Element Background
The sensing assembly consists of a center post, quartz piezoelectric
crystals, seismic mass and a preload bolt. Since the unit is operated in
a shear arrangement it will sense motion perpendicular to the base.
When the accelerometer is attached to a vibrating structure, the mass
exerts a shear force on the quartz piezoelectric crystal. This applied
force causes the piezoelectric material to produce an electric charge.
Since force is mass times acceleration (from Newton's second law), the
charge produced is proportional to acceleration, since m is constant.
This is represented by:
The sensing element offers many advantages over previous shear and
compression mode designs. Because of shear construction the
accelerometer is insensitive to thermal transients, transverse (cross-
axis) motion and the effects of base strain.
5.3 Low Impedance Output
Contained within the accelerometer housing is a miniature electronic
circuit. This circuit converts the high impedance charge signal
generated by the piezoelectric element into a low impedance voltage
output signal with an output impedance typically below 100 ohms.
The integral impedance converter is powered by an external power
source (coupler) that uses a two-wire cable between the
accelerometer and coupler. The signal and power share a common
line. The coupler provides a constant current source to the
accelerometer and decouples the DC bias (see Section 6.1.3) from the
measuring instrument. The useful signal is seen as a varying voltage
over an 11 VDC (nominal) bias.
m
F
a

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Low impedance accelerometers are ideally suited for applications
where long or moving cables are required; in high humidity or other
contaminated atmospheres. They eliminate the problems associated
with high impedance output types by providing a low impedance
voltage signal with enhanced high frequency response. The
calibration factors for these accelerometers are given in mV/g.
Figure 2: Diagram of a Low Impedance Acceleration System
1. Low impedance (voltage output) accelerometer
2. Coaxial cable
3. Coupler (constant current supply) or dual mode amplifier
4. Cable
5. Readout or analysis equipment
6Installation
6.1 General
For proper operation of shock accelerometers, care must be taken
during the installation process. Careful installation will result in
optimal high frequency response, accuracy and reliability.
6.2 Surface Preparation
A smooth, flat surface is necessary for both stud and adhesively
mounted accelerometers. If the surface is not completely flat, the
coupling between the accelerometer and the test article introduces
distortion into the measurement. A rough surface creates voids
between the mounting surfaces that reduce high frequency
transmissibility.
For optimum frequency response, the surface and hole preparation
should be according to the instructions in Table 3. The roughness
should not exceed 32 microinches (0.8 micrometers).

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6.3 Stud Mounting
The stud on both units is an integral part of the mounting base and
thus not removable. The following guidelines should be followed
when mounting shock accelerometers.
1. Drill and tap an adequate hole to ensure a flush mount of the
accelerometer. 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 accelerometer makes full
contact with the mounting surface (See table 3).
2. Completely clean the surface prior to mounting.
3. Apply a thin coat of silicon grease to both the accelerometer
and mounting surface.
4. Always use the proper sockets and a torque wrench when
installing accelerometers. Tighten the accelerometer to the
torque specified on the individually supplied calibration
certificate or as specified in Table 2. Do Not Over Tighten.
in-lbs
Nm
Accelerometer Types
18 ±2
2 ±0.2
8742A
30 ±5
3.4 ±0.5
8742A….M1
Table 2: Recommended Mounting Torque
Figure 3: Dimensions that vary by designation.

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Outline dimensions used in mounting that vary by series designation
are shown in Figure 3. Type designations that include the letter E are
sized in metric units.
Surface Dia.
D
L1 inch [mm]
L2 inch [mm}
3/8” minimum
10-32 UNF
0.156 [4.0]
0.315 [8.0]
1/2” minimum
¼-28 UNF
0.22 [5.6]
0.42 [10.7]
Table 3: Mounting Surface Preparation
6.4 Securing Cables
Figures 4 and 5 show the correct and incorrect ways for installing
cables. Allow a sufficient radius to ensure a proper strain relief. The
actual radius will depend on the cables being used. It is recommended
that cables be secured to the accelerometer mounting surface to
minimize cable and connector fatigue failures. Secure cables with a
cable clamp.
Figure 4: Correct Cable Strain Relief