Re: STG2 Outputs

[Jon Elson <jmelson-at-artsci.wustl.edu>]

JohnDRoc-at-aol.com wrote:

> I tested the phasing without a signal on the amp board - it's okay.  I had
> the both axes running okay with DAC0, but neither one with DAC1.  I had both
> axes running with all amps and DAC0.  My thought with the voltage signal is
> the +.004 is a + voltage, in that perhaps the amps can't compensate for it?
> All I know is that something is kinda fishy.  If I can get it running with
> DAC3 (also reading -.006) then I'll be reasonably confident that it's the DAC
> and perhaps even be happy, because I only need four of eight DAC's anyway.
> The question still remains, does anyone know how to reassign the output to
> DAC3 instead of DAC1?

Ok, I'm still trying to figure out what combinations worked, and what didn't.
But, I'm sure that .004 V offset is not enough to upset the system.  Figure it
out - if 10 Volts is supposed to provide a velocity of 120 IPM, then .004 V
should command a velocity of (.004 / 10) * 120 = .048 IPM, which is a barely
detectable crawl.

But, there might be some other problem in EMC that could be causing the
problem.  Check the parameters for the Y axis (called out in the .ini file
as axis 1) and see if any of them are different than the first axis, which you
are using for X, and is called out as axis 0 in the .ini file.  There are signs
on some of the values.  If these are different, the axis could also run away
due to increasing position error.  For instance, if your encoders are all
wired the same way, but you reversed the sign on the encoder tick size
to make the axis read positive for the correct direction of movement, that
could cause the axis to runaway, unless you also reverse both the motor
and tach wires.

Well, somebody else who had the code available in front of him
at the time gave some suggestions on how to swap a DAC channel,
so you can try that and see if it helps.  The .004 V offset is not, by itself,
an indication of trouble, but there could be a problem with that DAC
channel.

Jon