Non interacting zero and span. how?
Chris Eddy wrote:
> 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.
Unfortunately, it works the other way about. Assuming the zero bias
potentiometer has a low impedance, the two controls do not interact much
Your problem is that you are *not* zeroing it in the first place, but
setting an offset. The offset of course, represents the real offset
multiplied by the scale (span) figure; of course it depends on both.
The procedure you want is in three steps. Set the zero control for
*zero* output with zero input. Apply a 5V input and set the scale pot
for 4V output. Set the input back to zero, and adjust zero bias for the
desired 1V output.
See also: www.piclist.com/techref/index.htm?key=non+interacting
You must be a member of the
piclist mailing list
(not only a www.piclist.com member) to post to the