Interpreting PHD2 log and Guiding Assistant data

[Yash Singbal]

Gday Folks,

Have a couple of question about analyzing guide logs and GA output.

What does the X-axis on the frequency plot denote?  Is it N/worm cycle or time in seconds? What could I infer from the attached screenshot? Calibration was repeated after improving polar alignment.

What is the significance of RA and DEC drift rate in the GA output. Can this be used to choose guide exposures or guide speed?

Thanks in advance.

Cheers

Yash

[Brian Valente]

Hi Yash

comments inline below

On Fri, Sep 4, 2020 at 8:05 PM Yash Singbal <y.si...@gmail.com> wrote:

Gday Folks,

Have a couple of question about analyzing guide logs and GA output.

What does the X-axis on the frequency plot denote?  Is it N/worm cycle or time in seconds? What could I infer from the attached screenshot?

X-axis is in seconds, and this plot is designed to show you your periodic error. Here it shows you have a clear (but small) periodic error at 5.5 seconds.

 

Calibration was repeated after improving polar alignment.

What is the significance of RA and DEC drift rate in the GA output. Can this be used to choose guide exposures or guide speed?

no, not really. DEC drift rate shows your polar misalignment, which seems to be a bit high

I'm assuming you are testing your encoder CEM mount, which i think has some idiosyncracies regarding guidespeed. you have some thrashing about the RA at that 5.5 second period, which has come up a lot in recent posts.

you might go through past postings (or others with this mount and experience may chime in) regarding this anomaly

Brian 

 

Thanks in advance.

Cheers

Yash

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Brian Valente

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[Yash Singbal]

Cheers Brian,

Yes, I am testing the 60EC (have taken that to CN as it is not a PHD or guiding issue) but also wish to understand how to read PHD data independent of the mount.

I repeated the polar alignment (polemaster + sharpcap), the second guiding assistant run reported an error of 0.0 arcmin and sharpcap reported 13"

What about the RA drift rate in guiding assistant? What does that signify? Is there a desirable range? Should there be a correlation between max RA drift rate and max DEC drift rate in the GA output?

Yash

[Andy Galasso]

On Fri, Sep 4, 2020 at 11:47 PM Yash wrote:

Yes, I am testing the 60EC (have taken that to CN as it is not a PHD or guiding issue) but also wish to understand how to read PHD data independent of the mount.

Please check out this doc if you have not seen it already: https://openphdguiding.org/tutorial-analyzing-phd2-guiding-results/

 

What about the RA drift rate in guiding assistant? What does that signify? Is there a desirable range?

Should there be a correlation between max RA drift rate and max DEC drift rate in the GA output?

RA drift is also an indicator of polar alignment offset although other factors can also contribute such as atmospheric refraction and mechanical flexure.   I would not worry about RA drift since it is easily corrected with guiding. Dec drift is also easily corrected, as long as the drift is steady and in one direction (N or S.)

For an excellent reference on this topic see https://canburytech.net/DriftAlign/DriftAlign_1.html

[Yash Singbal]

Thanks Andy.