PHD2 Guiding fails on one side of the meridian, with Dec corrections in the wrong direction

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Niall MacDitto

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Aug 19, 2020, 7:49:41 AM8/19/20
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Hi all,

I have a C14 Edge HD on a Paramount MX+ Mount, with an SBIG 16803 camera.

I have been commissioning Sequence Generator Pro to allow me to sequence my captures.

Overall I have things working really well, with one problem. PHD2 Guiding fails when operating on one side of the pier.

Basically I have set things up so that SGPro communicates with the Mount via TheSkyX using the ASCOM driver for TheSky, with the following settings:

At the outset I was getting messages from SGPro that the sidereal time could not be sourced from TheSKy and that meridian flips could therefore not take place. I also noticed that the PHD2 Guiding logs stated that there was no information being made available on RA/Dec,  Hour Angle and the side of the pier where the OTA was situated. As follows:


I have not included the whole log, because this is just for illustrative purposes and things have progressed since that point.

I had forced a calibration and done darks during the early set up phase. However, in running sequences it became clear that when the OTA was on the west side of the pier, the guiding failed because the Dec corrections were in the wrong direction. This of course meant a positive feedback situation and a rapid and total loss of guiding control as illustrated by this graphic:

When I could force a meridian flip, the guiding worked perfectly on the other side of the pier. It seemed logical to me that since PHD Guiding had no information as to where the OTA was pointing that it didn't know which direction to apply the Dec corrections.

After some communication with the Software Bisque and following their advice to start the TheSkyX in Admin mode, SGPro was able to receive pointing information from TheSkyX and this was obviously being passed across to PHD2 Guiding, because the logs clearly reported the RA/ Dec, Hour Angle and side of the pier. Great!

However, when I went to guide with the OTA on the west side of the pier, the guiding failed again, but worked on the east side of the pier as before. I then forced a calibration with the OTA on the west side of the pier, thinking that perhaps a calibration was required with the correct pointing information, before the guiding would work correctly. Yes it worked, but when I did a meridian flip, the guiding failed again, this time with the OTA on the east side of the pier. After a recalibration the guiding worked again. So clearly, even though PHD2 Guiding knows which side of the pier the OTA is situated, for some reason it is still not reversing the correction direction.

There is a tick box in Guide>Advanced Settings> Guiding> Shared Parameters called "Reverse Dec output after meridian flip" which I have unticked, as I understood it should be when using Pulse Guide. However perhaps I need to have it ticked. Can you advise?

Here is a link to a file with the PHD2 logs and the SGPro logs as well.


Any help gratefully received.

Regards, Niall MacNeill

bw_msgboard

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Aug 19, 2020, 11:17:24 AM8/19/20
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Hi Niall.  Did you read the PHD2 help regarding the ‘Reverse Dec on meridian flip’ option?  Here it is:

 

  • 'Reverse Dec output after meridian flip' -  tells PHD2 how to adjust the calibration data after a meridian flip.  Some newer mounts track their 'side of pier' state and automatically reverse the direction of the declination motor.  Older 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 PHD2 provides the Meridian flip calibration tool to determine the correct setting automatically. It's also easy to figure out the setting manually with this quick experiment:
    • With the checkbox disabled, calibrate on one side of the pier, then move the mount to the other side.
    • If you are guiding via ASCOM or Indi or are using an 'aux mount' connection, just start guiding.
    • If you're guiding only via ST-4 and PHD2 has no scope pointing information, first select 'Flip Calibration' under the 'Tools' menu, and then start guiding.
    • In either case, if the guiding works normally, leave the box un-checked; but
    • if you see guiding run-away in declination, check the box and repeat the entire procedure, including calibration.

 

With the newer Software Bisque software, this box needs to be checked as I recall. 

 

I think you may have a misconception about how the pointing information is obtained by PHD2.  It doesn’t come via SGP, it is read directly via the mount connection – the same one that is used for sending guide commands.  I also think you were given bad (lazy-man) advice from SB regarding running things in Administrative mode.  This is not a good practice and isn’t required for astronomy applications on any modern version of Windows.  The problem is that once it’s done for one app, it has to be done for all the other apps that need to share an ASCOM connection.  I recommend that you sort this out and run everything with normal privileges – an administrative user account is fine but not ‘Run as Admin’.

 

Hope this helps,

Bruce

 

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Niall MacDitto

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Aug 20, 2020, 8:26:18 PM8/20/20
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Hi Bruce,

Firstly many thanks for your most informative response. It was indeed of help.

Yes I had read the section you highlighted for me and my next port of call was to check the check box and try it. However, I am surprised that, since PHD2 Guiding clearly knows which side of the pier the OTA is on, it can't just work out that the correction direction needs to be reversed, without having to told to do it. 

However, it is really good to have your confirmation that for Software Bisque software it is necessary to have the tick box checked. That is an easy fix.

Thanks also for clarifying that PHD2 Guiding is talking directly to the Mount.

In terms of running TheSkyX in Admin mode, I was unclear about that. SB's advice was to open TheSkyX in Admin mode, in order to authorise the software to communicate with other software, then shut it down and reopen it again normally. This worked.

Regards,

Niall

Geof Lewis

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Aug 21, 2020, 5:07:14 AM8/21/20
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Hi Niall,
Good to see you here.
As I understand it, the problem getting the Dec direction correct after a pier flip is not that PHD2 doesn't know side of pier, but that the mount manufacturers don't all implement their software (firmware) the same, so for some mounts PHD2 needs to be instructed whether to flip the Dec direction after a pier flip or not.
There is a list on PHD2's github page of the correct setting per mount, for those mount/models where that has been determined, most of which do not require the checkbox to be ticked, but SB is one that does.
There are just so many gotchas in this hobby, but at least you've got this one sorted 🙂
Cheers,

Geof
From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> on behalf of Niall MacDitto <niallm...@gmail.com>
Sent: 21 August 2020 01:26
To: Open PHD Guiding <open-phd...@googlegroups.com>
Subject: Re: [open-phd-guiding] PHD2 Guiding fails on one side of the meridian, with Dec corrections in the wrong direction
 

Niall MacDitto

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Aug 21, 2020, 7:34:36 AM8/21/20
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Hi Geof,

Way hey hey! That is great. I was pretty sure that ticking the box was going to get me sorted, but this makes it almost a certainty. Although as you noted, with this hobby, I will never be sure I have gotten past all the gotchas, until it is working in the observatory. Nevertheless I have a huge sense of relief.

I will send you a separate email with an update. I am pretty excited to be on the cusp of actually producing an image.
Cheers, Niall
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