[Diy_efi] DIY-WBO2 circuit now ceramic effects

[Bernd Felsche]

md4etal tapped away at the keyboard with:

> > md4etal tapped away at the keyboard with:
> >
> > > piezoelectric effect???
> >
> > If the heater's driven by PWM, that's electrically nowhere near a
> > piezo element.
> >
> > If the vibration is severe enough, you may however be able to detect
> > it at the sensor's other terminals.

> Please, think deeper here :  Ceramic resonator, piezo effect,
> ceramic media in the WB ........

> you were basically making a 10K-20K microphone element with the
> ceramic media in the WB sensor!!

There will always be a case of piezo effects on crystaline
structures exposed to physical distortion. An engine's exhaust is
probably not the most quiet environment on Earth.

However, an excitation of the outer shell does not necessarily mean
that the ceramic components will be exposed to a large amount of
direct mechanical stress. In fact; that's unlikely given that the
sensor would be constructed to allow differential expansion - else
the ceramic will fail very quickly under nominal operating
conditions.

Only if resonant frequencies are approached, is this likely to
become a problem. If the pulses are smoothed; at the expense of
disspating a fraction more power at switch-on and switch-off, the
higher harmonics can be signifcantly diminished.

The Bosch LSU documentation (downloadable from the DIY ftp site)
indicates, in the German-language version anyway, that the heater
current is pulse-width modulated, their heating graphs showing an
equivalent voltage.

That is NOT to say that all types of sensors can be driven at
arbitrary pulse frequencies.

Nor does it mean that PWM will be compatibable with analogue
DIY WB circuitry.

-- 
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