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Voltage reduction for voltmeter a/d conversion?

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raticus

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op amp voltage reduction

What is the recommended interface for a voltmeter input , in order to scale the input-voltage (+- 0-100v) to a voltage range of 0-5v suitable to feed into an a/d converter?
 

This is usually done with a resistive voltage divider. For not loading down the node being measured the two resistors should be large values. This produces a problem if the Thevenin output impedance of the divider is large and makes a voltage divider effect with the ADC input impedance. You have to make a judgement between the two sources of error in your resistor value choice.

If you want to add an op amp, you can make the see-saw inverting stage with the two resistors chosen for reduced gain. This will eliminate the divider effect of the ADC input impedance problem. To get the polarity back, use a second inverting stage.
 

The op-amp route definately sounds like the way to go.

Would there be any reference layout of the interface utilising an op-amp
that you could show me , or point me to?

Thanks
Raticus
 

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