Piezo optimization (parallel resistor)

[Erik]

Hi guys,

Just a few thoughts about the behavior of a piezo and a resistor. I've read that a resistor often is used to cool down a hot piezo. And i've seen the response of a piezo (i'm talking about the number of periods until the oscillation returned to nearly zero).

Now my idea: what happens, if i use a parallel resistor? If i compare it with a speaker then i think the oscillation will be much faster returned to zero (the generated voltage will be shorted) and will be less in amplitude. Can someone confirm that? Someone with a oscilloscope? And the next question is: i don't know how exactly the MD detects the hits, perhaps there are some oscillations needed, perhaps someone can say, if there is only needed the first one or if there are needed more.

There are no experiments from me by now, that was just a thougt in my head that i wanted to share and discuss.

Regards, Erik

Edit: is it better to choose high frequency piezos since the first oscillation is shorter and the detection can be done faster? Or is it a kimd of rms detection in a fixed time?

[dmitri]

Without going into much details, "cooling" should be done either with a voltage divider or with an inline resistor, not a parallel resistor.
The standard size of piezos, 20-30mm, don't have much affect on the quality of a signal. The design and contraction of pad have much more affect on the signal quality ( "ringing", long after hit vibration, length of the signal).