Periodic Error Correction Tab - Software Bisque Paramount MX User Manual

Paramount MX User Guide

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 ME and Paramount MX have 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 (around 20-
millionths of an inch) in the drive system 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.
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.
•
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 3-5
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.
As an example of periodic error versus seeing versus image scale, if the mount's total periodic error is
three arcseconds peak to peak and the local seeing conditions average four arcseconds, then the
tracking error caused periodic error is less than the tracking errors caused by seeing conditions, so
correcting the mount's periodic error is not critical.
However, if the local seeing averages one arcsecond and the optical system's image scale is one
arcsecond per pixel or smaller, you want to make sure that the periodic error is as small as possible for
optimal results.
90 | P a g e