Kistler 6233BD0250 Owner's manual

Instruction

manual

Pencil probe

Type 6233B…

for blast pressure

measurement

6233B_002-708e-07.22

Foreword

6233B_002-708e-07.22 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.

as expressly provided herein, no part of this manual may

be reproduced 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

Pencil probe Type 6233B…

Page 2 6233B_002-708e-07.22

Content

1.

Introduction .................................................................................................................................. 3

2.

Important information ................................................................................................................. 4

2.1

Warranty .............................................................................................................................. 4

2.2

Disposal instructions for electrical and electronic equipment ............................................. 4

3.

Sensor .......................................................................................................................................... 5

3.1

General functional description............................................................................................. 5

3.2

Application in air blast testing.............................................................................................. 6

3.3

Measuring chain .................................................................................................................. 6

3.4

Triggering methods ............................................................................................................. 7

3.4.1

Low current wire around explosive charge ............................................................. 8

3.5

Bandwidth optimization ....................................................................................................... 9

3.5.1

Natural frequency of sensor ................................................................................... 9

3.5.2

Sensor diameter and propagation velocity of blast wave ....................................... 9

3.5.3

Cable length and excitation current ...................................................................... 10

3.5.4

Coupler bandwidth ............................................................................................... 11

3.5.5

Sampling frequency of DAQ system .................................................................... 11

4.

Installation and operation ......................................................................................................... 12

4.1

General measurement setup ............................................................................................. 12

4.1.1

Distance from explosive charge ........................................................................... 13

4.1.2

Height above ground ............................................................................................ 13

4.1.3

Distance from obstacles ....................................................................................... 14

4.2

Sensor setup ..................................................................................................................... 14

4.2.1

Functional check .................................................................................................. 14

4.2.1.1

Check IEPE amplifier circuit using hand-held power supply / coupler

Type 5114 ............................................................................................. 15

4.2.1.2

Check measuring chain by lead burst test on sensor ........................... 15

4.2.1.3

Check measuring chain by small explosive charge .............................. 16

4.2.2

Orientation ............................................................................................................ 16

4.2.3

Fixation ................................................................................................................. 16

4.2.3.1

Tripod adapter Type 6550A10 .............................................................. 18

4.2.3.2

Pipe adapter Type 6550A20 ................................................................. 19

4.2.4

Thermal shock protection ..................................................................................... 22

4.2.4.1

Thermal protection foil Type 1191AAA10 ............................................. 22

4.3

Cable connections ............................................................................................................. 23

4.4

Coupler settings ................................................................................................................ 23

4.5

Triggering .......................................................................................................................... 24

4.5.1

Trigger box type 2525A04 .................................................................................... 24

5.

Maintenance and calibration .................................................................................................... 26

5.1

Maintenance ...................................................................................................................... 26

5.1.1

Sensor .................................................................................................................. 26

5.1.2

Storage case Z21537 ........................................................................................... 26

5.2

Calibration ......................................................................................................................... 27

Total pages 27

Introduction

6233B_002-708e-07.22 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, manufac-

turing, 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.

Pencil probe Type 6233B…

Page 4 6233B_002-708e-07.22

2. Important information

2.1 Warranty

The equipment supplied by Kistler Instrumente AG

Winterthur is covered by a warranty against faulty

material and workmanship.

This warranty extends 12 months from delivery date.

When submitting warranty claims, the items of equipment

concerned are to be delivered to the manufacturer's

works or to the regional distributor free of all charges,

and full details should be stated as to the nature of the

claims.

Settlement of warranty claims may be effected, at the

manufacturer's discretion, either through reconditioning

or replacement of the faulty items, or through a credit

note to their value.

Items of equipment damaged as a result of improper use

are not covered by the warranty.

Our responsibility under the warranty is strictly restricted

to the above provisions and we specifically decline any

liability for damages incurred consequent upon the use or

operation of our equipment.

Warranty claims for blast pressure sensors:

Due to the destructive nature of blast testing, warranty

claims for blast pressure sensors must be clarified on a

case-by-case basis.

2.2 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.

Sensor

6233B_002-708e-07.22 Page 5

3. Sensor

The Type 6233B… pencil probes are designed to

measure highly dynamic pressures in air blast testing. An

integrated amplifier circuit (IEPE) converts the charge

signal from the quartz sensing elements into a voltage

output. This allows driving of long cables up to several

hundred meters of length. The sensing element is aligned

to measure the side-on pressure of the blast wave

passing across the sensor body.

Distinguished characteristics are:

 Rise time <1 μs

 High natural frequency >300 kHz

 Voltage output (IEPE): integrated Piezotron

electronics

 Acceleration compensated

 Minimal bending sensitivity

Fig. 1: Pencil probe Type 6233B…

For full sensor specifications please refer to the data

sheet.

3.1 General functional description

Piezoelectric technology is ideally suited to measure

highly dynamic pressure signals over a wide range of

pressures. Pencil probe Type 6233B… is available with

measuring ranges from 0 … 25 psi, 50 psi, 250 psi, 500

psi and 1 000 psi. The characteristic pencil shape

minimizes the influence of the sensor geometry on the

blast wave propagation and the measured pressure

signal. Type 6233B… is pointed radially at the center of

the explosion or orthogonally to the blast wave. It

measures the side-on pressure of the propagating blast

wave.

The pencil body is made of corrosion-resistant, anodized

aluminum. A stiffer, stainless steel housing protects the

sensing element from mechanical deformations of the

pencil body which minimizes the sensitivity to bending

Pencil probe Type 6233B…

Page 6 6233B_002-708e-07.22

and ground shock effects. In the highly dynamic setting of

a blast test, the acceleration compensation of the sensing

element additionally avoids erroneous signals caused by

vibrations. The effects of thermal shock are small and

may be minimized further by applying a thermal

protection foil on the sensor membrane (refer to

Section 4.2.4 of this manual).

3.2 Application in air blast testing

Pencil type blast sensors are most effectively used in

testing scenarios where the direction of shock wave

propagation is clearly defined. In a side-on configuration,

the measurement is least affected by perturbations of the

pressure wave on the sensor. Side-on pressure is also

referred to as incident or static overpressure. A typical

use case is the free-field blast test, which aims at

characterizing the physical effects of an explosive

charge. Pencil probes are also used in blast impact

scenarios, where the destructive effects of explosions on

a protective structure are studied. These applications

also include testing of industrial safety technology.

Fig. 2: Visualization of free-field blast test setup

3.3 Measuring chain

The Type 6233B… pencil probes have a built-in charge

amplifier circuit and voltage signal output (IEPE:

Integrated Electronics Piezo Electric). Thus, no additional

Sensor

6233B_002-708e-07.22 Page 7

charge amplifier is required. The same technology is

referred to by the registered trademarks Piezotron

1

and

ICP

2

. A coupler provides the current needed to drive the

IEPE circuit and decouples the signal from the bias

voltage. This coupler may be a standalone unit or

integrated into the amplifier module of a data acquisition

(DAQ) system.

Fig. 3: Typical IEPE measuring chains

Standard coaxial cables with a BNC positive connector

configuration are used to connect the pencil probe to the

IEPE coupler and / or DAQ system. Kistler cable Type

1601B… is recommended.

If a standalone coupler is used, any high-speed DAQ

system / transient recorder may be used to digitize and

record the voltage signals. A number of commercial DAQ

systems include the option of IEPE coupling in the

amplifier modules. In this case, an external coupler is not

needed.

3.4 Triggering methods

Triggering of the data acquisition may be achieved by

multiple methods:



Low-current wire around explosive charge:

Explosion breaks the wire and stops the current. The

trigger time is defined by the physical expansion of

the explosive charge.



Flash detector:

Measuring device detects infrared emission of the

explosion. The trigger time is defined by the

progression of the fire ball and its light emission.

1

Piezotron is a registered trademark of Kistler Holding AG.

2

ICP is a registered trademark of PCB Piezotronics, Inc.

Pencil probe Type 6233B…

Page 8 6233B_002-708e-07.22

 Pressure sensor:

Measurement is triggered by pressure sensor. The

trigger time is defined by the pressure rise caused by

the arrival of the blast wave. The original detonation

time point is not recorded.

 Detonator:

Detonator device simultaneously produces high

voltage signal to ignite explosives and low voltage

signal to trigger measurement. The trigger time is

defined by the ignition signal. There may be a random

delay to the actual explosion.

 DAQ system:

Combined measurement and detonator system

simultaneously produces high voltage signal to ignite

explosives and starts measurement. The trigger time

is defined by the ignition signal. There may be a

random delay to the actual explosion.

Kistler recommends using the first method as described

in the next section.

3.4.1 Low current wire around explosive charge

A trigger wire with a low current is placed around the

explosive charge. Upon detonation, the wire is destroyed

and the trigger signal generator produces a voltage step.

Fig. 4: Scheme of recommended triggering method:

low-current wire around explosive charge

This method combines the following advantages:

 Safety:

Measuring chain is electrically decoupled from the

detonation chain.

Sensor

6233B_002-708e-07.22 Page 9

 Trigger time:

The trigger time very closely represents the

detonation time point. This is important to analyze the

propagation velocity of the blast wave (time of arrival).

Other methods may not account for delays between

the detonator signal and the detonation time, or may

not record the detonation time at all.

For simple and safe triggering of blast measurements,

Kistler recommends using trigger box Type 2525A04

(refer to Section 4.5.1 of this manual).

3.5 Bandwidth optimization

To determine the true bandwidth of the measurement

setup, it is not sufficient to know the natural frequency of

the sensor itself. Along the entire measuring chain, the

following factors influence the overall bandwidth:

 Natural frequency of sensor

 Sensor diameter and propagation velocity of blast

wave

 Cable length and excitation current

 Coupler bandwidth

 Sampling frequency of DAQ system

In the following sections, these factors are described in

more detail.

3.5.1 Natural frequency of sensor

The natural frequency is an inherent parameter of each

sensor type and cannot be influenced by the user. It

represents the frequency at which the sensor is excited

to resonance. For pencil probe Type 6233B… it has the

following value:

Natural frequency f

N

300 kHz

3.5.2 Sensor diameter and propagation velocity of blast wave

In the side-on measurement configuration, it takes some

time for the blast wave to travel across the sensor

membrane. The full signal is only measured once the

entire membrane is subjected to the pressure.

Pencil probe Type 6233B…

Page 10 6233B_002-708e-07.22

Fig. 5: Schematic of blast wave traveling across

sensor membrane.

The resulting low-pass filtering effect depends on the

sensor diameter and the propagation velocity of the blast

wave.

Example:

Side-on pressure p = 10 bar (145 psi)

Velocity of blast wave v = 1000 m/s

Diameter D = 5.5 mm

 Δt = 5.5 µs

Maximum frequency

kHz

s

f180

5.5

1

max





3.5.3 Cable length and excitation current

In order to avoid damage of the electronic instruments by

the blast, the coupler and DAQ system have to be placed

at a safe distance from the blast site. On the other hand,

the cable length has to be minimized to achieve

maximum signal dynamics.

Any cable has an inherent capacitance and acts as a

low-pass filter. The maximum frequency can be

estimated using the following equation:



2100

10

2

10

9

max

9

max













VL

m

pF

I

f

VC

I

f

max

= maximum frequency [Hz]

I = excitation current supplied by IEPE coupler [mA]

C = cable capacitance [pF]

L = cable length [m]

V = maximum signal amplitude [V]

Sensor

6233B_002-708e-07.22 Page 11

Example:

Signal amplitude V = 2.9 V

Cable capacity C = 100 pF/m

Cable length L = 100 m

Excitation current I = 4 mA → f

max

= 22 kHz

I = 8 mA → f

max

= 44 kHz

Thus, there are several ways to increase the maximum

frequency:

 Minimize cable length:

Optimize blast setup to minimize cable lengths. For

large-scale tests, use multiple synchronized transient

recorders / autonomous measuring systems.

 Increase excitation current:

Excitation currents up to 20 mA are applicable for

pencil probe Type 6233B. However, at high excitation

currents the sensor heats up considerably which may

reduce the lifetime.

 Decrease signal amplitude:

The signal amplitude can be decreased by using a

pencil probe with less sensitivity / higher pressure

range. Of course, the better dynamics are traded

against a loss in pressure resolution.

Minimize cable capacitance:

By using high quality coaxial cables, the cable

capacitance may be reduced to around 100 pF/m.

Due to technical reasons, further minimization of the

cable capacitance is not possible.

3.5.4 Coupler bandwidth

The IEPE coupler used has its own limitation in

bandwidth, which should be stated on the data sheet.

This also applies for DAQ systems with built-in IEPE

coupling. Although the maximum sampling frequency of

the DAQ system may be very high, the lower bandwidth

of the coupler may limit the achievable dynamics.

3.5.5 Sampling frequency of DAQ system

DAQ systems used to record highly dynamic blast

pressure events should fulfill the following minimum

specification:

Sampling frequency f

s

1 MSa/s

According to the Nyquist-Shannon sampling theorem, the

achievable maximum frequency that can be

reconstructed without loss of information is:

f

max

= f

s

/ 2

Pencil probe Type 6233B…

Page 12 6233B_002-708e-07.22

4. Installation and operation

4.1 General measurement setup

The pencil probe must be aligned in radial direction to the

center of the blast and ideally on the same height as the

explosive charge.

Fig. 6: Example of mounting setup

Blast propagation physics have to be taken into

consideration to define a suitable test setup. If the pencil

probe is positioned very close to the explosive charge,

only the primary blast wave is measured. Further away,

there are several pressure peaks of primary and reflected

waves. After a certain distance, only one high peak of

superimposed waves is seen (Mach stem).

The integral of the positive pressure curve is referred to

as impulse.

Fig. 7: Physics of blast wave propagation

Installation and operation

6233B_002-708e-07.22 Page 13

4.1.1 Distance from explosive charge

The following factors need to be considered to define the

best distance from the explosive charge:

 Ground reflections:

For improved interpretation of measurement results,

superpositions of ground reflections and other

secondary blast waves should be minimized as much

as possible. Depending on the height above ground,

the pencil probe should be placed close enough to the

explosive charge so as to only measure the primary

blast wave. The same principle applies with respect to

the distance from other obstacles than the ground. In

many cases, however, superpositions cannot be

avoided or need to be studied explicitly.

 Propagation velocity of blast wave:

Several pencil probes may be placed in a row with

respect to the center of the explosion in order to easily

determine the velocity of blast wave propagation.

 Damage by debris:

Depending on the type of explosive charge and the

quality of the surrounding ground, the pencil probe

should be placed far enough away from the

detonation in order not be damaged by debris (rocks,

wood splinters, shrapnel).

 Pressure overload:

The maximum pressure felt by the pencil probe must

not exceed the specified overload pressure of

5000 psi (350 bar). Mathematical models or

preliminary blast measurements at a safe distance

may be used to estimate the maximum pressure at

close distance.

In most applications, it is not possible to optimize all of

these factors. The required quality of the measured

signals must be weighed against the risk of causing

damage to the sensors.

Multiple pencil probes mounted at equal distances from

the explosive charge do not necessarily measure equal

pressure amplitudes. There are always asymmetric

effects in the chemical reaction of the explosion.

4.1.2 Height above ground

The following factors need to be considered to define the

best height above ground:

 Ground reflections:

For improved interpretation of measurement results,

superpositions of ground reflections and other

secondary blast waves should be minimized as much

Pencil probe Type 6233B…

Page 14 6233B_002-708e-07.22

as possible. Depending on the distance from the

explosive charge, the pencil probe should be placed

high enough above ground so as to only measure the

primary blast wave.

 Stability of fixation:

Mobile pencil probe fixations such as tripods cannot

be arbitrarily high due to the risk of falling over due to

the blast wave. The stability of a tripod may be

improved by weighing it down, for example by a

sandbag.

4.1.3 Distance from obstacles

In indoor blast tests or blast impact scenarios, additional

considerations have to be taken with respect to obstacles

such as walls, vehicles or other objects.

 Reflections:

For improved interpretation of measurement results,

superpositions of reflected secondary blast waves

should be minimized as much as possible. The pencil

probes should be placed far enough from any

obstacles so as to only measure the primary blast

wave.

4.2 Sensor setup

4.2.1 Functional check

Due to the destructive nature and high costs of blast

testing, functional checking of all measuring chains is

highly recommended prior to any detonation. There are

multiple options to perform a functional check:

 Hand-held coupler Type 5114: check

Sensor (IEPE circuit) + cabling

 Lead burst test: check

Sensor + cabling + coupler + DAQ

(1 channel at a time)

 Small explosive charge: check

Sensors + cabling + couplers + DAQ + trigger

(all channels simultaneously)

In the following sections, these methods are described in

more detail.

Installation and operation

6233B_002-708e-07.22 Page 15

4.2.1.1 Check IEPE amplifier circuit using hand-held power supply / coupler Type 5114

To check the proper functioning of the integrated IEPE

electronics, the hand-held Power supply / Coupler

Type 5114 may be used. This test may be done using the

real cable length of the final setup.

Please refer to the instruction manual of Type 5114 for

detailed operating instructions.

Fig. 8: Hand-held Kistler power supply / coupler Type

5114

4.2.1.2 Check measuring chain by lead burst test on sensor

A functional check of the entire measuring chain can be

done by breaking a thin lead pencil mine on the sensor

membrane. This is a well-known method used in the

characterization of piezoelectric sensors, because it

generates a very dynamic signal. The recommended

diameter of the lead mine is 0.5 mm and the length

approximately 5 mm.

Fig. 9: Commercial pencil used for lead burst test

and example of signal

Pencil probe Type 6233B…

Page 16 6233B_002-708e-07.22

4.2.1.3 Check measuring chain by small explosive charge

Prior to a large scale explosive test, it is recommended to

perform a small scale life detonation to check the proper

functioning of all measuring chains in the final

measurement setup. An explosive charge containing a

small fraction of the explosives of the actual charge is

used to generate a small blast wave which triggers a

measurement. The resulting signals can be checked for

malfunctions in the measuring chains.

4.2.2 Orientation

In order to avoid direct exposure to ground reflections,

the pencil probe has to be set up with the sensing

element facing up, away from the ground.

Fig. 10: Orientation of pencil probe: sensor (blue dot)

facing up

4.2.3 Fixation

The pencil probe fixation serves multiple purposes during

a blast measurement:

 Alignment:

The fixation helps to accurately point the pencil probe

towards the center of the explosion during the initial

arrival of the blast pressure wave. Proper alignment is

critical to obtain the correct peak pressure and should

be within an angle of ±5° of the radial direction.

 Stable fixation:

The primary blast wave and its reflected waves exert

considerable force on the fixation. If the sensor is

pushed out of the fixation or the entire setup falls

over, this may result in damage of the sensor

membrane, pencil tip or cable connector.

Installation and operation

6233B_002-708e-07.22 Page 17

 Mechanical damping:

Excessive ground shock may induce a signal

superimposed on the pressure signal. Since the

ground wave travels faster than the pressure wave in

the air, a noisy signal is commonly seen shortly before

arrival of the blast wave. The fixation needs to provide

mechanical damping to minimize the effects of ground

shock.

Two standard fixation types are recommended:

 Tripod fixation

 Pipe fixation

Pencil probe Type 6233B…

Page 18 6233B_002-708e-07.22

4.2.3.1 Tripod adapter Type 6550A10

For pressure impulses <1 000 mbar*ms (see section 4.1)

the pencil probe can be installed on a standard tripod.

Such an installation is most convenient for mobile use

and variable test setups. It may be used equally on level

and rough surfaces.

The Kistler tripod adapter Type 6550A10 features a

standard ¼-inch UNC thread (DIN4503 / ISO1222),

which is compatible with most commercial tripods used

for example in photography. It is recommended to attach

the tripod adapter at the rear end of the pencil probe in

order to delay any pressure reflections.

Fig. 11: Attachment of tripod adapter Type 6550A10 at

rear end of pencil probe

To prevent tipping of the tripod, it should be stabilized, for

example by a sand bag.

Fig. 12: Tripod installation including stabilization with

sand bag

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Kistler 6233BD0250 Owner's manual

Kistler 6233BD0250 Owner's manual

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