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Old 30th July 2005, 02:42 PM   #1
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Default Need amp for DC input --> AC output

This is not an audio application but the fruits of these labors will help fund Alephs and other upcoming projects.

Here's the problem.

A gage produces a +/- 2.5 VDC ouput proportional to the temperature. That's the input.

For a whole variety of reasons, the ouptut of this yet to be created black box must be a proportional AC signal. The output characteristics should mimic that of an LVDT (linear variable differential transformer). The excitation of the LVDT will and can be provided by an outside source --- 2.5kHz ~ that part is already working. Output voltage should be about the same ~ 1-2.5 VAC.

Money? No problem, this isn't hobby work

Help a brotha out...
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Old 30th July 2005, 04:52 PM   #2
mzzj is offline mzzj  Finland
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variable gain-amp fed by oscillator and your dc-signal?
Analog multiplier sounds even better. MPYxxx series from TI comes to my mind first. Or check what Bob Pease @national has got to say about "analog multipliers and stuff"

If you need better precision than 0.5-1% I think that you better to go digital. AD-CPU-DA

OK, now send me the money, thats the problem for me for most of the time
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Old 30th July 2005, 10:12 PM   #3
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Does one oscilate then amplify or amplify then oscilate?

Bob Pease is cool!
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Old 30th July 2005, 10:46 PM   #4
mzzj is offline mzzj  Finland
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Quote:
Originally posted by chipco3434
Does one oscilate then amplify or amplify then oscilate?

Bob Pease is cool!
neither.
stable sine wave from oscillator is fed to one of inputs in multiplier and your DC voltage to second input. Ouput is ac signal with amplitude controlled by dc-input signal. Lets say that you build oscillator with 1vac out, feed this to multiplier X input and dc signal to Y input. Output of multiplier is then X*Y

LVDT "simulator", straing gage replacement for LVDT or what are you trying to build?
I miss your point that output should be 1-2.5Vac
And i didnt think long enough, reference voltage is also needed to offset multiplier.

Attenuate input dc signal by 10/3 ratio, feed to G=1 opamp that has 1v reference so that output is between 1-2.5V dc. Feed this to multiplier X and 1vac(from separate oscillator or your LVDT exitation signal attenuated suitably ) to multiplier Y input. Done.



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Old 30th July 2005, 10:52 PM   #5
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If I understand correctly all you need is not more and not less than AM-modulator. Right?
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Old 31st July 2005, 01:30 PM   #6
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Quote:
all you need is not more and not less than AM-modulator. Right?
That seems correct.... and simple.
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Old 31st July 2005, 01:38 PM   #7
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Try an AD654 -- the chip has only been around for 20 years.
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Old 31st July 2005, 03:20 PM   #8
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Whaaat?
AD654 is a VCO, a FM-modulator
???
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Old 31st July 2005, 03:29 PM   #9
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I don't require the variable frequency output... Just a proportional ~ unity (or less) output at 2.5 kHz.

The DC could be converted to an RMS voltage? Yes?
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Old 31st July 2005, 05:03 PM   #10
mzzj is offline mzzj  Finland
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Cant be so damn difficult
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