PHD2 guiding after meridian flip

[L Harris]

Last night I was doing another set of tests on PHD2 guiding + EQMOD + SGP. I prefer to get PHD2 guiding properly befpore starting other programs. The guiding was fine. I moved to a new source that was higher up and caused a meridian flip. The guiding went all over the place. While standing there bewildered it occured to me that this is what would happen if (1) the corrections did not allow for dec changes and (2) PHD2 took no notice of meridian flips.

(1) was apparently allowed for somewhere because I recall setting it.

(2) I have no idea.

Any comments or advice welcome.

Lawrence Harris

[bw_msgboard]

Hi Lawrence.  From the Help file under Basic Use (help index/meridian-flip):

 

If you are using a German equatorial mount (GEM), you will usually have to do a "meridian flip" around the time your image target crosses the meridian.  This means you will move the telescope around to the opposite side of the pier and then resume imaging.  Doing this invalidates the original calibration, typically because the declination directions are now reversed.  If you are using an ASCOM (or 'aux' ) mount interface, your calibration will be adjusted automatically and you can simply resume guiding (assuming you haven't also rotated the camera or focuser).  If you aren't using an interface that returns pointing position, you will need to take action to adjust the guider calibration.  You can, of course, simply do another calibration on the current side of the pier, a process that will typically take only a couple of minutes.  Or, you can use the pull-down menu item under 'Tools/Modify Calibration' to "flip calibration data" and then resume guiding immediately.  

 

With a few mount types, the controller reverses the direction of the Dec motor based on side-of-pier.  If so, you handle that by using an option in the ‘Guiding’ tab of the Advanced Dialog.  Here’s the Help file section on that:

 

'Reverse Dec output after meridian flip' - tells PHD2 how to adjust the calibration data after a meridian flip.  Some mounts track their 'side of pier' state and automatically reverse the direction of guide commands in declination.  Other mounts do not do this.  In either case, PHD2 needs to know if the mount will automatically change its behavior based on side-of-pier.  You may have difficulty finding information about how your mount behaves in this respect, so it's probably easiest to just run a quick experiment.  With the checkbox disabled, calibrate on one side of the pier, then move the mount to the other side.  If the guiding works normally, leave the box un-checked; but if you see run-away in declination, check the box and repeat the entire procedure, including calibration.

 

You probably need to take SGP out of the mix temporarily and just do the meridian flip by hand to see how your mount behaves.  Once you have the above option set correctly, you can forget about it.

 

Good luck,

Bruce

 

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[L Harris]

Thanks Bruce

I follow all that - so I'll now need to copy/paste it in my notes for next session.

Thanks

Lawrence

[L Harris]

I've had a good re-read of the PHD2 manual (well v 2.6.1) although mine is v 2.6.2. It does actuall imply that if your mount is ASCOM - and the EQMOD is ASCOM - then it should know all about reversing signals where needed. The first guiding that was done after the flip was appalling. So I'm now wondering what went wrong - because it is going to happen again. I suppose I could do a new cal, but this is going to affect automation as well. If it can't reliably guide after a flip, them something is wrong with my settings. Another query: the notes imply that only the dec is reversed. I wonder why?

Lawrence

[steve]

El 26/09/2016 a las 18:11, L Harris escribió:
> I've had a good re-read of the PHD2 manual (well v 2.6.1) although
> mine is v 2.6.2. It does actuall imply that if your mount is ASCOM -
> and the EQMOD is ASCOM - then it should know all about reversing
> signals where needed.

Hi
The only flip related thing I set in EQMOD was the 'Allow Auto Meridian
Flip'. I'm not sure if this can be automated. During the flip I cancel
everything: APT and PHD2, plate solve on the other side and centre once
again on what I solved before the flip, find a new guide star and
restart APT. It would be great if we had this automated and I didn't
know about it!
HTH and clear skies,
Steve

[bw_msgboard]

Hi Lawrence.  There’s no need to re-engineer this, the calibration flipping logic has been in place for years, and SGP users routinely do automated meridian flips without problems.  You may have a different problem entirely.  In fact, I was going to ignore your original post because I think it’s pointless to try to correct problems without knowing exactly what they are.  Telling us “The guiding went all over the place” or “The first guiding that was done after the flip was appalling” tells us nothing useful at all.  The simplest thing to do is disengage SGP and perform the meridian flip and guiding tests manually.  If you don’t like the results and changing the ‘reverse Dec’ option doesn’t work, send us your guiding and debug logs and we’ll figure out what’s happening.  And doing a new calibration isn’t going to affect automation, but it’s something you should do before you run the manual test.

 

Bruce

 

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From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of L Harris

Sent: Monday, September 26, 2016 9:12 AM
To: Open PHD Guiding

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[L Harris]

Thanks again - you are quite right in all respects.

Lawrence