PEC sense vs encoders #pec #encoders


 

Can I have PPEC if I only use PEC sense based on HAL sensor on RA worm, or do I need encoders for that? And if I add encoders, do I still need PEC sense then? It's not clear to me what is the benefit of having encoders with OnStep.


Khalid Baheyeldin
 

On Sat, Nov 20, 2021 at 04:11 AM, vzr wrote:
Can I have PPEC if I only use PEC sense based on HAL sensor on RA worm, or do I need encoders for that? And if I add encoders, do I still need PEC sense then?
You do not need encoders to have the PEC sensor to record and playback the periodic error of your worm.

It's not clear to me what is the benefit of having encoders with OnStep.
Encoders in OnStep are mainly for pointing (e.g. disengage the clutches, manually move it somewhere, and the
encoders tell OnStep where in the sky it is pointing).

Encoders in OnStep are not for RA rate correction.
And they are experimental. Only a small percentage of OnStep users have them.


George Cushing
 

A Hall sensor is activated by a permanent magnet that's mounted on the worm axis. Other sensors can be used like an eccentric attached to the worm axle that closes and opens a switch. Celestron used this system for limit switches on the CGE. Another common device is an optical interrupter that is attached to the worm and breaks the UV light transmission between an LED and a phototransistor. The Celestron Nexstar GPS11 mount used this system.


The sensor is the green PCB. Behind it you can just make out a slotted disk that's screwed to the end of the worm. On the back of the PCB there is an optical sensor that the disk usually blocks. Only when the slot in the disk aligns with the sensors LED and detector can it operate. You can see the sensors 4 pins on the lower right front of the PCB. Optical sensors of this type can be found in dead printers.