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Re: To PEC or not to PEC..
We create the encoder curve using proprietary PEMPro software and a precision reference motion that is accurate to +- 1/10 arc sec. The mount's movement is compared to that precision reference and the deviation is recorded and used to create a PE curve. This is just like using the precise motion of the Earth's rotation that you measure using a distant star when you do a PEMPro run on the night sky.
We run 5 worm cycles to create the PE curve. We check to make sure all 5 cycles lie on top of each other, which is an indication that all the gearbox components are doing the right thing. The curve is created and downloaded and we do another 3 cycle run with PE turned on to verify that the compensation curve is correct. All the data from these curves are stored here for future reference in case there are any questions about performance of a particular mount. If someone has a situation where they would like to restore their factory curve, we can download it in their CP4 over the internet.
From: Dale Ghent daleg@... [ap-gto]
Sent: Fri, Dec 7, 2018 1:09 pm
Subject: Re: [ap-gto] To PEC or not to PEC..
Question, Roland - how /do/ you create the factory curves? Do you haul each mount out to the observatory and wait for a suitably clear and stable night, or do you have a (literally) in-house test bench made for doing this with repeatable precision at any time?
> On Dec 7, 2018, at 1:48 PM, chris1011@... [ap-gto] <ap-gto@...> wrote:
> ..that is the question (apologies to the Bard)
> Hi Astronuts,
> We have been shipping out 1100 mounts in the present production run, and as most of you know the mounts are tested here and loaded with a PE curve into the CP4 memory. Our mount technician, Dave, spends a considerable amount of time testing the native PE of the mount. He then creates a very accurate and smooth PE curve and loads that curve back into the mount. The resultant accuracy with PE turned on is 1 arc sec Peak to Peak or less (Rms typically comes in under 0.2 arc sec). I just saw on Crowdy Nights where one of our new customers ignored the loaded curve and created his own right off the bat, under very poor conditions to boot. The resultant PE looks worse than with PE turned off!
> When we send out these mounts, a very accurate PE curve is in memory and can be turned on by the user. It is very accurate and does not need to be updated, even though we also send you a copy of PEMPro so you can create your own PE curve to replace the one already in memory. Don't be in a big hurry to create your own PE curve and load it into the CP4 memory. By all means play with the software, measure the PE with and without compensation turned on and even create your own curve and compare it to the one that's factory loaded into memory (PEMPro allows you to do that), but DON'T just overwrite what is there in memory to begin with. In fact it's a good idea to bring the factory curve up with PEMPro and save it on your laptop. That way you can always load it back into the CP4 if your own curve doesn't work out.
> On top of that, if you are going to create a PE curve, make sure that you have a good night with good stability where the stars don't pulsate or move around due to upper atmosphere disturbances. Then also follow instructions so that your resultant curve is smooth, because if you load a ragged curve into memory, all those pops and sniggles will be played back faithfully and impact your tracking and guiding in negative ways.
> You have been handed a fine violin that was tuned to perfection by Dave, our expert tuner. So practice that Mozart concerto with the instrument as is, before turning it into a slack key guitar.
Posted by: Dale Ghent <daleg@...>
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