piclist 2000\05\21\074146a >
Thread: Non interacting zero and span. how?
www.piclist.com/techref/index.htm?key=non+interacting
picon face BY : Spehro Pefhany email (remove spam text)



At 07:22 PM 5/20/00 -0400, you wrote:
>I have a question that is just burning me up.  And when I try to solve
>it I get a mental block.
>
>To simplify the problem, say I have an op amp circuit with an input
>signal of 0-5VDC and a desired output of 1-5VDC.  I have a zero and a
>span pot.  Normally, I build this circuit with the zero pot and the
>signal in question summed with two resistors into the + pin of the amp.
>Then wrap the output back to the negative pin with a pot for the span.

Try a pot connected as a rheostat in *series* with the signal (summed
to the non-inverting input) and adjust the 1V level by summing to the
inverting input (fixed feedback resistor).
You'll need a -ve reference for this to work.

If you want to use a +ve reference it might be easier to buffer the
zero adjust voltage with an additional unity gain op-amp and use your
original circuit, but with the span adjust pot again in series with the
signal to the non-inverting input.

Best regards,

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