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Piezoelectric acceleration sensors

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					 18       Acceleration sensors                                                                                                             A       B


Piezoelectric acceleration sensors
Measurement of acceleration up to 35 g

                                                                                                                                                         a
                                                                                                                                                                 U

b Acceleration measurement
using piezoelectric bending
elements (bimorphous
strips).
b Micromechanical accelera-
tion sensor (please enquire).
b Low temperature-
dependence.
b High sensitivity.
b Wide measuring range.




Range                                             Technical data / Range
Dual-channel sensor
                                                  Part number                              0 273 101 141             0 273 101 150          0 273 101 131
With two identical, but independent,              Block diagram                            X                         –                      –
piezo-ceramic bending strips. These are                                                    min. typ.     max.        min. typ.     max.     min. typ.     max.
connected so that the output voltages of          Measuring range
each channel are phase-opposed.                     at UV = 5 V                    g 1)    –35     –      +35        –35     –      +35     –35    –         +35
Suitable for pcb mounting.                        Frequency range (–3dB)           Hz      0.9     –      250        0.9     –      340     0.9    –         340
                           0 273 101 141          Supply voltage UV                V       4.75    5.00   5.25       4.0     5.0    5.25    4.0    5.0       5.25
                                                  Supply current IV                mA      –       –      12         –       –      15      –      –         15
With two sensing directions offset to each        Open-circuit voltage
other by 90°. Suitable for pcb mounting.            at zero acceleration           mV      –45     –      +45            UV /2 ±60 mV       UV /2 ±60 mV
                            0 273 101 150         Calibrated sensitivity at room
                                                    temperature                    mV · g–1 57.5   60     62.5       57.5    60     62.5    57.5   60        62.5
                                                  Calibrated sensitivity at
With one sensing direction only. In this            operating temperature          %       –       –      4          –       –      –       –      –         –
direction, acceleration leads to a 180°           Operating-temperature range      °C      –45     –      +95        –45     –      +95     –45    –         +95
phase shift of channel A, whereas the
channel B phase shift is 0°.                      Electrical output
Suitable for pcb mounting.                        Current-carrying capacity        mA       0.9     –      –         –       –      –       –      –         –
                            0 273 101 131         Capacitive loadability           pF       1200 –         –         –       –      –       –      –         –
                                                  Pin assignment
Applications                                         Pin 1                                  UV = +5 V                Output B               Output B
Used in automotive occupant-protection               Pin 2                                  Output B                 UV = +5 V              UV = +5 V
systems for triggering the airbag, the seat-         Pin 3                                  UV = +5 V                Data                   Data
                                                     Pin 4                                  Test input               Test input             Test input
belt tightener, the roll-over bar, or the seat-
                                                     Pin 5                                  Ground                   Output A               Output A
belt locking systems. Used for instance as           Pin 6                                  Output A                 Housing, ground        Housing, ground
the impact sensor for monitoring impact              Pin 7                                  Housing, ground          –                      –
loads during transportation. Since the            1) Acceleration due to gravity g = 9.81 m · s–2.
lower frequency limit is 0.9 Hz, this sensor
can only be used to register acceleration
changes.
                                                  When subjected to acceleration, the piezo-                     Test signal
Design and function
                                                  ceramic bends by as much as 10–7 m.                            A fully operational sensor generates a
The heart of this acceleration sensor is a
                                                  For signal processing, the sensor is pro-                      positive output pulse when +5V are briefly
piezo-ceramic strip of polycrystalline
                                                  vided with a hybrid circuit which is com-                      applied across its test input. If there is an
sintered material. When electrically polar-
                                                  prised of an impedance converter, a filter,                    open-circuit in the signal path, this out-
ized, this material displays a piezoelectrical
                                                  and an amplifier. These serve to define the                    put pulse will be missing, and if the
effect: That is, when pressure is applied,
                                                  sensitivity and effective frequency range.                     bimorphous strip is broken the signal will
the mechanical loading results in charge
                                                  The filter removes the HF signal compo-                        exceed +5V.
separation, or a voltage which can then be
                                                  nents.                                                         For the versions with two bimorphous
picked-off by electrodes.
                                                  The lower frequency limit of 0.6 Hz is                         strips, the output pulse must appear at
The piezo bending element comprises a
                                                  defined by the piezo element itself. Using a                   each output.
bonded structure containing two inversely
                                                  supplementary test input, the sensor’s
polarized piezo strips, the so-called bi-
                                                  electronic functions can be monitored as
morphous strips. These have electrodes,
                                                  well as piezo-strip integrity.
and are bonded to a center electrode. This
configuration has the advantage that the
pyroelectrical signals caused by tempera-
ture fluctuations compensate each other.
B               A                                                                                                                                                                    Acceleration sensors                 19




Dimension drawings.                                                                                                                                                               Block diagram of dual-channel sensor.


0 273 101 141


         30                                                                     13,6                                                                        3,81    X
                                                                                                                                                                   R4
                          20,85 ± 0,3




                                                                                           0,6- 0,1




                                                                                                                                                      0,7
                                                                                                                                                 3,5+ 0,5
                                                                                                                                                                                         ++




                                                                                                                                                    -




                                                                                                                                                                   43,82 ± 0,2
                                            9




                                                                                                                                                                                         –
                                                 0,65 + 0,1
                                                              4,1± 0,2




                                                                                                                     123456 7
                                                                                                               2,8
                                                                                      4,35+ 0,15
                                                                                          -
                                                                                            0,05
                                                                                                               2,54                                                                      ++
                                                                         4,9± 0,2                                     15,24
                                                                                                                                                                                         –
                                                                                       X                                                                        4,4 ± 0,2




0 273 101 131/150



                                                                                                      18,8 + 0,2
                                                                                                           + 0,1



 1                                                                   1                                                                                      X
                      6
                                                                                                                     3,8 ± 0,4




 2                                                                   2
                                                                                                                       + 0,2
                                                                                                                     20+ 0,1




 3                                                                   3
 4                                                                   4
                                                                                                                                 0,7+ 0,2




                                                                                                                                                                    8 ± 0,3




 5                    6                                              5
                                                                             1± 0,4




 6                                                                   6



                                                                                       1,4± 0,4            X

                                                                                                                                                                                 Installation instructions
                                                                                                                                                                                 The acceleration sensors must be installed
                                                                                                                                                                                 so that the baseplate is either vertical
                                                                                                                                                                                 or horizontal referred to the direction of
                                                                                                                                                                                 acceleration or deceleration.

Installation position.
A, B, M Directions of measurement

                    Baseplate vertical referred to direction                                                             Baseplate parallel to direction
                    of measurement.                                                                                      of measurement.
                    0 273 101 141                                                                                        0 273 101 150                                                    0 273 101 131
                    Deceleration in direction of measurement                                                             Acceleration in A direction                                      Acceleration in A direction
                    Channel A output voltage                                                                             Channel A output voltage                                         Channel A output voltage
                                        UV                                                                                              UV                                                        UV
                    UAA <    ,                                                                                           UAA >     .                                                      UAA <    ,
                         2                                                                                                     2                                                               2
                    Channel B output voltage                                                                             Acceleration in B direction                                      Channel B output voltage
                                        UV                                                                               Channel B output voltage                                                 UV
                    UAB >                    .                                                                                          UV                                                UAB >        .
                                        2                                                                                UAB >               .                                                    2
                                                                                                                                        2




                                                                                                                                                            A

                                                                         M




                                                                                                                                    B                                                             A