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Design

The basic element is a micromechanical

system with a double tuning fork made of asilicone crystal, which has been housed in a

small electronic element on a sensor board.

Let us take a look at a simplifiedrepresentation of the double tuning fork. It is

connected at its "waist" to the other silicone

element, which we have omitted here in orderto make the illustration clearer to understand.

The double tuning fork consists of an exciter

tuning fork and a measuring tuning fork.

SP28-46

SP28-47

Exciter tuning fork

Measuring

tuning fork

Connection to

other silicone

body

The exciter

tuning fork

oscillates in

resonance

Alternating voltage

with a frequency of

11 kHz

The measuring

tuning fork

does not

oscillate in

resonance

Function

If an alternating voltage is applied, the siliconetuning fork can be caused to vibrate withsympathetic oscillations.

The two halves are harmonised in such a waythat the exciter tuning fork oscillates in the

resonance at exactly 11 kHz and themeasuring tuning fork at 11.33 kHz. If an

alternating voltage with a frequency of exactly11 kHz is applied to the double tuning fork, the

exciter tuning fork vibrates with sympathetic

oscillations, but not the measuring tuningfork.

A tuning fork which is vibrating with

sympathetic oscillations, reacts more inertlyto the effect of a force than a mass which is

not oscillating.

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Design and Operation

What this means is:

Whereas the measuring tuning fork and the

rest of the sensor moves together with thevehicle when the effect of a rotational

acceleration is felt, the oscillating part of thedouble tuning fork (exciter tuning fork) follows

this movement with a certain time lag.Consequently, the double tuning fork turns

within itself in the same way as a cork opener.

This turning motion results in a modified

distribution of the charge at the tuning forkwhich is measured by electrodes, analysed by

the sensor electronics and transmitted as asignal to the control unit.

SP28-48

Resonanceoscillation

Turning

moment