Re: [CAD_CAM_EDM_DRO] Servo amplifier boards.

johndroc@... wrote:

> While I was straining my brain (because I'm running out of hair to
> pull out),
> trying to figure out why I can't get the Y axis tuned, I happened to
> put a
> meter across the DAC's, from the STG board. The X and Z, at rest,
> were
> -.006 and -.015, respectively. The Y is around +.004. I think this
> explains
> why I can't seem to get it to balance and why the tach signal is not
> able to
> compensate. Does anyone know what the signal out of the DAC "should"
> be or
> has anyone measured it? When I take the signal off of it, I have no
> "drift"
> in the amp and it doesn't take off, at all. There is a way to balance
> it, by
> replacing a resistor on the amp. I'd hate to do that, though, if it's
> a
> defective STG card. Thanks.

This is pretty normal. They use a bunch of resistors and op amps to
bring the signal level from the DAC they use from a 0 .. +5 V range
to the -10 V .. +10 V range needed. If any of these resistors are off,
or the op amps have more than a minimal offset error, or the errors
add up in the same direction, then you get these zero offsets. The
bal pot should be able to set them to zero. Really, out of a 20 Volt
range, even .015 volt is quite small, about .075% of full scale range.
There is a feature in the EMC program that allows you to compensate
these errors by moving the software zero. They are set by parameters
in the .ini file. I note that the Y axis is the smallest of your offset
errors.
I really don't think this is your problem.

Jon