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NNTP-Posting-Date: Thu, 24 Oct 2002 00:07:56 -0500
From: "Big John"
References: <3DB33417.3B414EF1@bellatlantic.net> <3DB5F2CF.77C1FFC2@bellatlantic.net>
Subject: Re: piezo voltage sense
Date: Thu, 24 Oct 2002 00:59:48 -0400
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It may not be as easy as you think. I worked with various accelerometers
in a job I had a couple of years ago. There are different types. Piezo
accelerometers are a charge source rather than a voltage source. They have
a very high output impedance and you need a special charge amplifier that
has a very high input impedance to get a signal that you can work with.
Charge amplifiers are not cheap.
Many of these accelerometers have a built in amplifier and are called
"integral amplifier" accelerometers. Most are designed to be fed by a DC
constant current source. Usually around 2ma (and up to 27 volts or so
IIRC). There are also voltage fed types but they are less common. This
makes them much easier to work with as integral amp accel's have a usable
signal with a low output impedance that can be fed into op-amps directly.
For more info check out some of the manufacturer's data. Try Bruel &
Kjaer, PCB, and Endevco to start.
Hope this helps,
garwood wrote in message <3DB5F2CF.77C1FFC2@bellatlantic.net>...
>Thanks. As you can see i studied economics in college.
>i have a piezo accelerometer that is linear 1 v per g of accel or decel
>i want to sense a - or + 10g force on +x axis or -x axis. the
>accellerometer is +10 in +x axis and is +10 on (otherwise negative leg)
>of -x axis. i feel a diode bridge to rectify output to + on either leg
>will suffice then a simple comparator for sensing the +10v threshold.
>N. Thornton wrote:
>> garwood wrote in message
>> > i have a piezo strip that creates ac + - ac voltage when disturbed. i
>> > want to sense both + and - 10v ac . I think that i can use a bridge
>> > diode (with rc for smoothing) to output dc signal then use a comparator
>> > to trigger > 10volts for a trigger. The + and - signals shall be 20-50
>> > mseconds in duration. I do not care about under or over +-10volts.
>> > what do you think? Thanks
>> I think you could do with explaining clearly, this seems pretty
>> ambiguous. I dont even know what youre trying to do here. Perhaps then
>> you will get much more help.
>> Regards, NT
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