Re: PEM Curve From Keypad Versus PEM Pro

Roland Christen

The PE curve that is in the CP is generated using multiple cycles with PEMPro. As the mount teeth wear in during multiple slews over many days and weeks of operation, the PE curve may change significantly from the original factory measurements.

PEMPro averages multiple cycles to get a smooth PE curve that is devoid of fast moving disturbances that occur on a real star under less than perfect seeing conditions (i.e. the star is moving around a lot due to atmospheric disturbance).

The PE curve that is generated using the keypad simply records one worm cycle into the same memory in the CP controller. It is not something stored in the keypad. The action is the same as PEMPro where nothing is stored on the computer, but the keypad stores only one cycle and does not average multiple cycles.
based on experience, the keypad PE correction can reduce the error by a factor of 4 to 5, and the multiple averaged PEMPro can probably reduce it by a factor of 8 or better.


-----Original Message-----
From: M Hambrick <mhambrick563@...>
Sent: Thu, Jun 11, 2020 3:12 pm
Subject: [ap-gto] PEM Curve From Keypad Versus PEM Pro

I have some novice questions about the PEM curves for A-P mounts:

Is there a difference between the PEM curve that can be generated from the Keypad versus the curves that are generated by using PEM Pro ? The description in the Keypad manual describes a fixed 7 minute recording cycle for the 1100 Mount (one revolution of the worm). The description of PEM-Pro in the GTO-CP4 manual implies that the PEM curve can be created using more than one revolution of the worm.

The CP4 manual also mentions the PEM curve that is loaded into the CP4 before they are shipped to the customers. Is this curve created using PEM-Pro with multiple worm cycles, or is it generated using the Keypad function using just one cycle ? Do I have to enable (run) this pre-loaded curve from the Keypad, or is it always running in the background ?

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