RA and DEC vary by an unexpected amount, PHD2 Unable to guide

[Claudio Nunez]

HI all,

I'm quite new to auto guiding since I started last October 2018. My last two sessions have being awfull PHD is not working properly as it gives me this warning: RA and DEC vary by an unexpected amount and it's being unable to guide. These last two sessions I haven't done any star alignment as my intention was to Plate Solve (see this: Discussion on CN )

Also, my PA is way OFF. So I wonder if the star alignment procedure has something to do with the auto guiding and I'm guessing the PA error also is critical here.

Log FIles here: 

https://openphdguiding.org/logs/dl/PHD2_logs_rMWP.zip

Mount Celestron AVX

Imaging OTA: WO Zenithstar 81 APO

Guiding Scope: Starfield 60mm

Guiding CAM: Altair GP Cam 130M

Any comments and help will be much appreciated

Thank you

[Andy Galasso]

Hi Claudio,

I do not see the problem you are referring to in the logs that you uploaded. The debug log shows that there were no warnings at all in that session, including warnings about RA and Dec guide rates.  Perhaps you meant to upload a different log file?   You can search for the word "Alert" in the debug log to see any warnings that PHD2 displayed.

Your guiding actually looked pretty good in the 4h and 1h guide sessions ...  total RMS error of less than 0.9" with equal contributions from RA and Dec ... should have been giving you nice round stars in the imaging OTA.

Feel free to upload the log files that had the warning and we can take a look at them.

Andy

[Claudio Nunez]

Hi, Andy definitely the wrong file. I have difficulties using the PHD2 to upload log files. The window is too small.  Here is the one that is giving me troubles. 

https://openphdguiding.org/logs/dl/PHD2_logs_BmRG.zip

I forgot to say that in my last two sessions I introduce new hardware a Pegasus Astro Ultimate Powerbox that helps me with cable management as well as powering the whole right. I doubt that this is creating problems. But certainly, it has an impact on my DEC balance.

Any help would be much appreciated.

Thank you

[Andy Galasso]

Hi Claudio,

I went through each of the alerts in the log and summarized the cause and solution.  Please note that pretty much all of these issues could be effectively addressed by following the recommendations in the PHD2 Best Practices Guide.  My responses below are a bit terse, so feel free to follow-up if you would like more details.

22:32:33.519 00.000 7412 Alert: PHD2 is not able to make sufficient corrections in RA.  Check for cable snags, try re-doing your calibration, and check for problems with the mount mechanics.

22:32:33.519 00.000 7412 Alert: PHD2 is not able to make sufficient corrections in RA.  Check for cable snags, try re-doing your calibration, and check for problems with the mount mechanics.

Cause: stale calibration

Fix: re-calibrate when you setup the gear with the guide camera at a different orientation

22:40:59.055 00.001 7412 Alert: Little south movement was measured, so guiding will probably be impaired. This is usually caused by very large Dec backlash or other problems with the mount mechanics. Read the online help for how to deal with this type of problem (Declination backlash).

23:06:14.287 00.000 7412 Alert: Little south movement was measured, so guiding will probably be impaired. This is usually caused by very large Dec backlash or other problems with the mount mechanics. Read the online help for how to deal with this type of problem (Declination backlash).

23:25:54.843 00.000 7412 Alert: Little south movement was measured, so guiding will probably be impaired. This is usually caused by very large Dec backlash or other problems with the mount mechanics. Read the online help for how to deal with this type of problem (Declination backlash).

00:31:21.001 00.000 7412 Alert: Little south movement was measured, so guiding will probably be impaired. This is usually caused by very large Dec backlash or other problems with the mount mechanics. Read the online help for how to deal with this type of problem (Declination backlash).

Cause: large dec backlash

Fix: ok to ignore the alert (check the option to not show it any more.)  PHD2 is advising you that you have a lot of dec backlash so you can be aware of it, the calibration is still ok

22:40:59.317 00.000 7412 Alert: The RA and Dec rates vary by an unexpected amount
22:40:59.332 00.015 7412 Calibration alert details: Expected ratio at dec=10.4 is 0.984, actual is 1.829

23:06:22.700 00.000 7412 Alert: The RA and Dec rates vary by an unexpected amount
23:06:22.715 00.015 7412 Calibration alert details: Expected ratio at dec=-0.1 is 1.000, actual is 1.409

23:26:01.282 00.000 7412 Alert: The RA and Dec rates vary by an unexpected amount

23:26:01.309 00.027 7412 Calibration alert details: Expected ratio at dec=0.3 is 1.000, actual is 1.418

Cause: huge polar alignment error -- ~110 arc-minutes as measured by guiding assistant

Fix: use one of the built-in polar alignment tools in PHD2 to get your polar alignment error down to below 10'.

23:19:18.366 00.000 7412 Alert: PHD2 is not able to make sufficient corrections in Dec.  If you have just done a meridian flip, check to see if the 'Reverse Dec output option' on the Advanced Dialog guiding tab is wrong.  Otherwise, check for cable snags, try re-doing your calibration, and check for problems with the mount mechanics.

Cause: huge PA error, dec corrections could not keep up with the drift

Fix: polar alignment

00:20:38.228 00.000 7412 Alert: RA Calibration Failed: star did not move enough

Cause: calibration at high declination Dec = 59.4 deg with small calibration step size combined with huge drift from polar alignment error

Fix: polar alignment, calibrate near dec zero and re-use calibration (no need to re-calibrate)

00:32:06.258 00.000 7412 Alert: PHD2 is not able to make sufficient corrections in RA.  Check for cable snags, try re-doing your calibration, and check for problems with the mount mechanics.

Cause: huge RA drift at declination 59.4 deg.

Fix: polar alignment

A separate issue I noticed is that you were using 200ms guide camera exposures and getting lots of Star Lost errors.  You should use no lower than 1.0 second exposures.  You can run the guiding assistant to get a recommendation of guide exposure.

Andy

[Claudio Nunez]

Hi, Andy Thank you so much for your comments. I will certainly follow your recommendations and I know my PA was awfull. Not as the previous Log file that I send. 

I'll try again tonite as its clear here. I'll post if the problem persists.

Clear Skies