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PEC with GM8 492 Controller

 

Hello All,
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I have a non-goto Losmandy GM8 with the 492 digital drive that is working quite well for me.?
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I have been running some guiding "tests" over the past week just to see what kind of tracking performance I get w/ and w/o guiding, w/ and w/o PEC etc. I am actually quite happy with the results and I am seeing further improvements with PEC applied.?
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My assumption was that once generated the PEC is stored within the 492 and would automatically get applied to the next session. But from what I can tell, that does not appear to be the case. Is that true? Does the PEC generation protocol need to be re-run each time I start up the controller??
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Sequence of events:
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1. After successful guide calibration with PhD2, I started autoguiding
2. After ~10 mins of autoguiding, I hit the PEC button on the 492 panel and the red LED started flashing telling me that it was in recording
3. After ~8 mins (worm period on GM8), the red LED stopped flashing telling me that the PEC had been applied.?
4. I continued autoguiding with PEC turned on and I saw an improvement to an already good tracking performance.
5. After wrapping up my tests, I turned the 492 unit off and turned it on again.?
6. PEC light was off by default (I was thinking it would remain ON since I had already gone through PEC generation). When I hit the PEC button, it started flashing again.....so effectively restarting PEC generation?
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I really don't mind redoing it (I need to redo guide calibration each time anyway, so an additional 8 mins is no big deal), but just wanted to understand how the system works. The manual does not provide much information about this.?
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Many thanks!
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Avi
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Avi,
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Your understanding is correct: The PEC table evaporates when the power is cycled. So you must redo the PEC each session.
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Part of the reason is because of the memory technology used in the older drives.
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Another part of the reason is that the 492-equipted mounts do not have any feedback from the motor/worm assembly (aka encoder or PEC sensor).
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At one point Meade and Celestron (if my old memory isn't failing) used the term PPEC for Permanent PEC.
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Best regards,
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Mark Christensen
 

The 492 was a development of the Celestron 1990 Ultima PEC System. It was a microprocessor quartz controlled closed loop system. For the G11 and Celestar Deluxe mounts the feedback loop was dropped and step motors were employed. All three mounts had PEC, but I don't believe they were PPEC (permanent PEC) with a memory. The Celestar Dlx was notorious?for failing to even record the?error stream. PPEC requires about 1-2K to store.

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As you can see the 492 has an Intel 80C52 MCU. IIRC it had 256 bytes of internal memory and could support up to a 16K EPROM. The 64K EPROM couldn't be used for on-board programming.?

When I look at the 492, I remember?the first mainframe I worked on in the late '60s, it also had 64K main memory. That required 30+ ferrite bead plates each with 4,092 hand woven iron beads, more than 6 months work for a weaver. And barely over 20 years it's all reduced?to this.

The I-8051/2 design is still widely?copied, used and greatly?reduced in size and flash memory is now up to 2T in SD and smaller formats.

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