nuckollsr(at)cox.net Guest
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Posted: Tue Sep 05, 2006 4:00 am Post subject: Dividing one voltage by another using an op amp? |
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At 11:59 AM 9/4/2006 -0400, you wrote:
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<livingjw(at)earthlink.net>
Bob, All,
I seem to remember from my analog computer class (yeh, I'm that old) that
you can divide using an op amp. Can anyone point me a circuit which does
this? Thanks. One of my students built an AoA indicator a couple of years
ago with a cheap differential pressure chip, but he brought the signal out
and into a digital computer that we already had installed on the airplane
for storing flight data. He then divided it by the dynamic pressure using
software. It worked great. I thought it would be fun to see how simple it
could be done using analog circuits. These pressure measuring chips are just
a couple of dollars and you would need two of them. One differential for the
angle and one absolute pressure chip for the dynamic pressure.
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It's a special class of op-amp called a four-quadrant mulitiplier.
An exemplar part is the AD633 with a data sheet at:
http://www.analog.com/UploadedFiles/Data_Sheets/277093686AD633_e.pdf
See figure 7.
However, like all analog systems, these devices have their warts
for leakage, offset, drift, tempco, etc. etc.
A PIC microcontroller with on-board a/d could put this effort
on less mushy ground.
Bob . . .
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