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Thread: Non interacting zero and span. how?
face BY : Robert A. LaBudde email (remove spam text)

<x-flowed>At 07:22 PM 5/20/00 -0400, Chris wrote:
>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.
>The big complaint form customers is that the zero and the span interact
>a lot.  My quest is to change the circuit so that the zero pot
>accurately sets the 1V level at 0V in, and then adjust the span pot for
>5V out at 5V in.
>By the way, the application is converting to 4-20mA.  Any output where
>the ratio of low to high is 1:5 is acceptable.  It does not have to be
>1V and 5V.
>The application in mind has split rails, but it would be nice to have a
>single supply solution for those other jobs too.  Any grand ideas come
>to mind?

1. What is your current circuit?

2. What type of op-amp are you using?

3. Is an inverting configuration acceptable?

Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: @spam@ralTakeThisOuTspamlcfltd.com
Least Cost Formulations, Ltd.                   URL: http://lcfltd.com/
824 Timberlake Drive                            Tel: 757-467-0954
Virginia Beach, VA 23464-3239                   Fax: 757-467-2947

"Vere scire est per causas scire"


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