Gemini Users Manual 44
4.3.2 The PEC Submenu
The PEC submenu (“Setup → Mount Parameters → PEC”) has these options:
• Train PEC
• Clear Data
• Turn PEC On/Off
• Delay Correction
• Drift Correction
• Smooth Data
• Average Data
• Restore Data
• Maximum Pulses
The Gemini PEC can store 2 separate sets of correction data. One set, called the “current
data set” is used to actually correct for periodic error. It is initially stored when the first
PEC training is completed. The other set, called the “backup data set” is used for
backing up and combining PEC data. These data sets will be described in more detail in
the following sections.
4.3.2.1 Train PEC
Until an initial (current) data set has been recorded, no PEC data is available to the
Gemini software. Also, a CMOS reset or the execution of “Restore Defaults” or “Clear
Data” clears all PEC data and, in all these cases, only two PEC menu items, “Train PEC”
and “Maximum Pulses” are visible and available for use.
Once you select “Train PEC,” you start a training session, where your task is to keep an
object (preferably a star near the meridian) centered in the crosshair of an eyepiece or at a
given CCD pixel location. You have about 10 seconds to center the object used for the
first training, while a countdown (“Training PEC –xx”) is displayed. A short beep marks
the start of a training session, and another beep marks the end of training after one
period. The length of a training session will vary according to the period, normally one
worm rotation on your mount. This is about 4 minutes on a G-11, HGM-200 and MI-
250, 5.33 minutes on an HGM Titan, and 8 minutes on a GM-8 and CI-700. You can
interrupt the training session by depressing the MENU button on the Hand Controller.
The countdown time for subsequent training runs will vary, since training is always
started at the same point on the worm. Thus, you may need to wait up to 8 minutes (on a
GM-8 or CI-700 mount) to do additional training runs. You may do as many training
runs as you desire.
After each training run, the PEC data just entered is stored in the current data set, and is
immediately available for use. Any previous data is moved into the backup data set
where it can be manipulated by several of the other PEC commands.
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