Periodic Error Correction Tab - Paramount Fitness ME II User Manual


A black-filled square indicates that the joystick is centered and the mount is not slewing via the
joystick inputs.
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A green-filled square indicates that the joystick is issuing slew commands to the highlighted axis.
Note that the joystick handle can be moved diagonally so as to issue slew commands both axes at once
(N, E, S, W or NE, NW or SE, SW). In this case, two adjacent squares will be green.

Periodic Error Correction Tab

The Periodic Error Correction tab is used to generate and manage periodic error curves for the Bisque TCS
control system. The Bisque TCS PEC Table tab is used to retrieve, save, delete and view the periodic error
correction curve. The Compute PEC Curve tab is used to determine the optimal periodic error curve based
on mount tracking data.
The Paramount has precision worms and gears that slew the mount's axes and track the earth's relative
motion compared to the stars. As the worm rotates, imperfections in the drive system (on the order of
one twenty-millionths of one inch) introduce a predictable "back and forth" drift at the eyepiece.
This drift is called periodic error and is present in all worm and gear drive systems. The mount's periodic
error can be virtually eliminated using periodic error correction. Here is an overview of the periodic error
correction process. Step by step details follow.
How to Train and Apply Periodic Error Correction
1. Create a tracking log that records the magnitude of the mount's periodic error over three or more
revolutions of the worm. See "Collecting and Using Periodic Error Tracking Data" on page 142 for
details how to create a tracking log.
2. Open the tracking log in the Compute PEC Curve tab.
3. Fit an optimal periodic error curve to the tracking log data.
4. Save and permanently store the optimized periodic error curve to the mount's firmware.
5. Turn on the Apply PEC Corrections checkbox to apply periodic error corrections.
The importance of applying periodic error correction to tracking depends on several factors:

The magnitude of the mount's periodic error. All mounts have slightly different periodic error
due to machining variations. The greater the periodic error, the more noticeable the back and
forth "drift" in right ascension and more elongated stars in photos.

The scale of the imaging system. Tracking demands for an imaging system with an image scale of
four arcseconds per pixel or larger are less demanding than on a system with an image scale of
one arcsecond per pixel or less.
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The local seeing and weather conditions. A turbulent jet stream caused by nearby mountain
ranges (here in Golden, Colorado, for example) can produce average seeing errors from three to
five arcseconds per pixel and rarely better. A laminar, more stable atmosphere in regions like
Florida or Southern New Mexico in the USA often produce periods of sub arcsecond seeing.
Paramount User Guide
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