Recording PEC for CGEM mount

[Ronald Scotti]

I am trying to determine the best way to record PEC data for my CGEM mount.  I run Phd2 under Ubuntu, I guide using the PPEC routine for RA, I get reasonable results (<1.5") depending on sky conditions.  I would like to see if I implemented PEC in the mount if I can improve on that.  I recorded (to files) 15 cycles of PEC data (after finding starting index) while I was guiding with PPEC.  The problem is that none of the cycles (data) look remotely the same.  They are drift corrected and the peak amplitudes all are about the same, but the phase of the 'cycles' are all different and they don't appear to be correlated in a way that I could average them for a meaningful result.  Should I be trying to record PEC while guiding using PPEC?  (because PPEC is being 'predictive' will it constantly change the PEC data curve? - I recorded the PEC data over 2 long guiding runs of 30 minutes and 50 minutes) Can I record PEC data (at the mount) while running with no guide pulses (guiding assistant)?  (what is being sent to the mount, if anything, while Phd2 is tracking but not sending guiding pulses? - I have read that it sends the amount of RA error to the mount which would constitute the PEC data curve.- I have not tried this, but will).

thanks,

[bw_m...@earthlink.net]

I think you need to get a better understanding of how the mount is going to be programmed.  Isn’t there an app that accepts either raw tracking data or guiding software corrections in order to build a PEC?  In any case, you shouldn’t be using PPEC for this.  You’re also getting bad information about how PHD2 works.  If guiding is disabled, as it is when using the Guiding Assistant, nothing at all is being transmitted to the mount.  The PHD2 guide log will have a record of all the measured guide star excursions, but that it’s it.  If you want to capture the raw tracking behavior of the mount, you can run the Guiding Assistant for multiple worm cycles but you’ll have to be sure the polar alignment is good enough that the guide star isn’t lost.  But as I said, there should be something more to this process, some piece of software that can at least do some smoothing and outlier rejection to keep seeing disturbances from being baked into the PEC.

 

Good luck,

Bruce

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[Bryan]

Ron

All Celestron mounts can use the Celestron free utility, PECTool, to record PE and train the mount in order to correct PE.

Bryan

[mj.w...@gmail.com]

Hi Ronald.

There are at least two ways to implement Permanent PEC, if your mount has that.

By setting the mount to record the guiding corrections.

Or recording the unguided star movements:

1. Set the mount to Train PEC, so that it records the PHD2 guiding corrections.

That might include using PHD2 PPEC, to get the best RA guiding.

In the case of my Meade LX the Train runs for three worm turns.

Once that is recorded then sometimes there's an Update mode which can improve the PE even further.

2. Record the star movements recorded by PHD2 in the GuideLog with guiding off, as in a Guide Assistant run.

Use a tool such as PemPro to work out the correction curve required to correct the PE.

Upload that to the mount's PPEC.

I'm told the eccentricity of the large worm-wheel has little impact on PE, it's mostly the worm itself.

So repeated runs in the Cal position will work.

Michael

Wiltshire UK

[Ronald Scotti]

All,,

thanks for your responses.  As usual, things are complicated.  I control all my equipment using Linux based OS, so I cannot use most third party programs that don't run under that OS.  However, I can use the hand controller commands (or simulated ones) to find the mount index and record a PEC curve (to mount or to a file) over multiples cycles.  As you can see some say NOT to use PPEC to guide while trying to record PEC data, other say it is fine.  I am of the latter group, but don't have experience to support that position.   I was not sure about what Phd2 sent to the mount, so I asked (I assumed as it seems that it only sends instructions for corrective pulses when guiding and not the actual guiding error value either when guiding or not).  My polar alignments are usually good (< 3' as reported by Phd2) so I can run the guiding assistant over multiple cycles and I will have to try the evaluation period of PEMPro to see if I can produce a viable PEC curve from that data (I don't want to pay for something that is not going to produce helpful results).  

The mounts manual on the subject of PEC recorded is somewhat 'dated,'  it recommends to 'manually' guide while recording PEC (that's not going to happen)!  But it does seem that I should be able to record PEC while guiding with Phd2 using a different algorithm.  Can you recommend what algorithm to use and with what settings that would make Phd2 'simulate' simple manual guiding corrections?  

[mj.w...@gmail.com]

HI Ronald

If you're not using the PemPro method ie you are Training the PEC, you have to guide the mount as good as possible.

If PHD2 PPEC improves the RA guiding then you should use it.

Michael

Wiltshire UK