Periodic error correction with an autoguider

[jambouk]

My mount (azeq6) allows permanent periodic error correction.

It seems, one can use a guiding system for this.

If i were to use a stand alone auto guider on a scope, is the software in the mount's handset clever enough to know exactly which of the errors are down to periodic errors, and which are down to my dodgy polar alignment, and only remember and replay the periodic errors when applying the correction?

Thanks.

James

[Davey-T]

I think you can use the guider to record the PEC  but have read many posts on PEC and guiding fighting each other to control the mount, also seems to depend on software , ie  PHD, Maxim etc.

Dave

[jambouk]

Thanks for that. I was really meaning with a guide cam which didn't need connecting to a laptop, like a synguider.

James

[brantuk]

I was wondering exactly the same thing yesterday James - good question for Skywatcher I reckon - hopefully FLO can chip in here.

[ollypenrice]

As I see it...

PEC training, which can be done best by using an autoguider, trains only the RA drive and the only information the system has comes from RA measurement. If that measurement is made with polar misalignment then that misalignment's effects will be there in the measurement and will be unique to that particular misalignment. However, I can't imagine them amounting to much in an 8 minute turn of the wheel. I'd be confident that, in reality, one set of corrections would work for a range of PA errors.

I don't use PEC with autoguiding but some do. Since some find it helps and some don't I guess you have to try it.

Olly

[andrew s]

James, 

You can train your PEC using images taken with the guide camera or your main camera. Personally I would use the  camera with the largest image scale - most arc secs per pixel. The data collected suffers from many errors due to seeing, polar misalignment, wind gusts etc. To do it well it is best to average many runs. If implemented properly the software should remove any drift due to polar misalignment.  I don't know  your mount or software so I don't know how easy that would be for you. Training PEC must be done without any auto-guiding action. 

With PEC active you can also auto-guide to remove any residual error - PC based or stand alone. The issue of PEC and auto-guiding interacting has not been an issue for me. If properly set up and if sensibly implemented by the mount supplier nested control loop should not be an issue. I was a control engineer many years back and implemented many control systems using feed-forward (like PEC) and multiple  feedback (auto-guiding) loops with no issues.

If the mount drive is poor with many fast changes in rate as the worm turns it will difficult to improve just by PEC and auto-guiding. I would be tempted to lap the worm and wheel to see if I could improve it and or any other dive gears. However, only do this if you know what you are doing.

Regards Andrew

[jambouk]

Thank you all.

So it would seem the mount should probably be drift aligned to make polar alignment as accurate as possible before attempting an autoguided periodic error learning exercise.

I was hoping the software in the handset would be clever enough to identify the cyclical periodic error over several cycles from the other constant corrections the autoguider would be making for non-perfect polar alignment.

Hopefully FLO/Skywatcher will have the definitive answer.

Thanks again all.

James