weird scatter plot..

[Sandy MacPherson]

I'm trying to use PHD's logs to sort out some RA guiding issues.  I noticed a weird scatter plot - maybe someone can explain why RA seems to be sticking to certain +/- values or zero.

I've attached the guide log and a screen shot of the plot. 

[Andy Galasso]

Hi Sandy,

Yeah, that is pretty weird. There's some RA oscillation with the mount pulling one way and then the other with phd2 sending corrections to bring it back to center.

I think it would be interesting to see how your RA is acting without guiding corrections. Have you tried running the Guiding Assistant (which will disable guide output) and looking at the resulting guide log?

Andy

[Sandy MacPherson]

yeah, i did run the guiding assistant for a bit in that log, but I don't see anything...I went back and found the past few weeks of logs and they show this pattern in the scatter plots too

[Andy Galasso]

On Wed, Sep 7, 2016 at 9:05 PM, Sandy MacPherson <funkys...@gmail.com> wrote:

i did run the guiding assistant for a bit in that log, but I don't see anything

ah, ok, I see that now in Section 19.   Since we're interested in seeing the RA curve, I think you should let it run for at least one full RA worm cycle (9 minutes?) so we can see the full curve.

Andy

[Sandy MacPherson]

have to wait for a clear sky!

[Sandy MacPherson]

but I have a full cycle from a little while ago

[Andy Galasso]

Sandy, ok, thanks.  We can see some 1-3 arc-second amplitude spikes with a period of about 11 seconds in your RA drive.   The spikes are a bit of a problem for phd2 because they are larger than seeing variations (where you set your min-motion) so phd2 tries to correct them and this results in the oscillations in guiding.  From your original posted data, it looks like you have tuned your RA aggressiveness to dampen the oscillations and mostly avoid over-correcting.

Despite the oscillations, your'e getting a decent 1.1" RMS RA guide error. That may be good enough guiding depending on your imaging scale in your main camera.  If not, I think you'll need to identify the mechanical origin of the RA oscillation and fix it at the source. You'll need to ask the AVX mount experts for ideas about that.

Andy