Re: [CAD_CAM_EDM_DRO] Re: Servo amp connections needed. Where should I go from here?

sleyed wrote:

> Hey Thanks Chris,
> There is no tach on the motor I am using.This is a mishmash of
> parts.I was trying to simulate the tach input at the same time as the
> signal hoping it would null out somewhere near zero volts on each
> input.

This will not work. There is essentially an open-loop op amp in there,
comparing actual to commanded velocity. You MUST have a valid
velocity input, or else remove this servo loop from the circuit.
(Some servo amps have a jumper to do this.)

> It may be a case where I need a slight negative to null it.

You can't null an open-loop amplifier. The gain is too high, a fraction
of a mV drift will cause it to swing full scale.

> You are correct in stating there is a + and - 10 voltDC terminals.
> I was considering putting a 2k pot as a variable voltage divider
> across these +/- terminals to get a 20volt spread with 0 volts at
> center.Then using the pot wiper as the output to the signal

Yes, that will work fine.

> and tac
> inputs respectively.

But, as I say, you either need the tach feedback to close the velocity
loop, or you need to deactivate the velocity loop. That will take info
from the manufacturer.

Jon