INDI Library v2.0.4 Released (01 Oct 2023)

Bi-monthly release with minor bug fixes and improvements

Re:Multiple PEC cycles

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I have a CGEM mount, I use the PEC record tool in the Indi Control Panel. Would it be possible to have that tool take multiple PEC recordings instead of just a single one. Typically you would like to record 6 -9 PEC runs and average them for a better result. If it is an easy change it would be nice to have it continue to take PEC cycles until you tell it to stop, just making sure that the "full" ones (all 88 index steps) are saved to a file.

7 months 1 week ago #90815

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Replied by Tim on topic Re:Multiple PEC cycles

What are the steps you go through to do this? I’ve always been interested in PEC training, but didn’t know where to start. I have a CGX by the way. Thanks.

5 months 3 weeks ago #91689

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Replied by Doug S on topic Re:Multiple PEC cycles

Hi Tim,

Although somewhat outside the scope of this INDI forum, one traditional way to get a Celestron mount PEC curve is to use CPWI (free), and PECTool (also free). You drive the telescope during the test with your guider and CPWI, and then record N PEC curve sessions (batch process, averaged) with PECTool. After it's done, upload the curve to the mount using PECTool. Once uploaded, it is semi-permanent (until a new curve is done or disabled). FYI, PEC must be enabled on each mount power-up (hand controller or INDI mount - control tab). On startup, the index position of the worm gear will be found, and then you can start the PEC playback.

You can find both free Celestron software programs (CPWI and PECTool) on the Celestron support site:

Good luck and CS,
Doug S.
RASA11, Celestron CGX-L, ASI183mc Pro, 60mm guider + ASI290mm mini, ASI EAF focuser, PPB, Rpi4-4Gb+SSD, Powered USB3 hub, hardwire Ethernet.
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5 months 3 weeks ago #91709

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To take my PEC cycles, I aim the scope at a target near the Meridian and Equator, set up Phd2 to be prepared to guide on a star in that area. In the mount Control panel, in Ekos, I select (in Motion Control) to find the mount index. The mount will move slightly and then indicate that the index is found. I then begin guiding in Phd2 and let that settle down after a few minutes. Then back in the control panel I select 'record PEC' and the recording begins of the 88 steps for my CGEM mount, while Phd2 is sending guiding commands to the mount. After that is complete a file is written, I save it in a folder labeled PECData. If guiding is still ongoing I can then select 'record, again and a second PEC set of data will be collected (for the CGEM mount it takes about 8 minutes to run a full gear cycle). (Note: i ran this PEC record process with two different guiding algorithms; first with PPEC and second with Hysteresis, just in case the PPEC algorithm somehow interfered with the PEC collection process) I have done this for multiple PEC cycles, which I then read into an Excel file (the files saved are of CSV type) In Excel I can average and smooth the curves to produce a final single PEC curve. Back in EKOS I load that file, in the Control Panel, and then select playback. The PEC data is now in the mount and being played back to correct the PEC of the mount.

Later I ran the Phd2 guiding assistant for several PEC cycles with PEC off (Disabled in Control Panel), with PEC engaged and with a negative of the PEC curve loaded (I have read that sometimes an inverted PEC curve is required). I found no consistent improvement in the outcome of the Guiding Assistant. So for my mount it does not seem that PEC (in the mount) will improve guiding. So I will continue to use the PPEC algorithm in Phd2 to compensate for PEC in the mount.
The following user(s) said Thank You: Jerry Black
5 months 3 weeks ago #91749

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