On Fri, 16 Jan 2009 21:58:54 -0500, Bob Engelhardt
wrote:

I'm using a dc motor & a servo amp to run the lead screw on my lathe.
The servo amp is an Advanced Motion Controls model 25A20:
http://www.a-m-c.com/download/datasheet/25a20i.pdf

I'm setting the speed with an analog input on pins 4 & 5 ("REF"). This
is described as "Differential Reference Input (±10 V Operating Range,
±15 V Maximum Input)". My assumption was that this voltage could go to
15v, but beyond 10v there would be no additional effect on the output.
I was wrong. The output continues to increase as REF increases to 15v.
I didn't check if it was linear in the 10 - 15v range.

The question is: is it a bad idea to use it in the 10-15v range? It
might be useful to have the extra output in certain special cases. E.g.
rapid reverse.

I've used a lot of AMC amps and don't recall having to go beyond a 10V
input to get full output. Do you have the gain pot turned all the way
up? I assume you're running in voltage mode, not current mode, yes?

The input is probably limited to +-15V because the op amp at the input
has a +-15V supply and most op amps don't like voltages outside their
supply on the inputs. If you need a 15V reference to get full output,
it shouldn't be a problem. But I think you should be able to get there
with a 10V signal, or even less.

--
Ned Simmons