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Pulsar Dome off by a few degrees after calibration

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#1 carlosgib

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Posted 07 July 2019 - 03:52 AM

Hi Group,

 

Having complete the installation of my Pulsar Dome observatory and have the drive automation unit installed and program as well, I managed to calibrate the drive after changing magnet so that the encode could read it better and after a single rotation it  was calibrated. I am using both Park and the Home position at the same angle of zero degrees (basically pointing polarize). The dome shutter window center points to Polaris (already done a polar alignment), so my mount is at zero degree before I started the calibration.

 

However when the calibration was completed the drive panel screen showed 358 degrees and is spot-on the center of the shutter window, if I instruct the dome to move at zero/360 degrees it will move away from the shutter center.

 

When I originally installed the Drive and the encode I am pretty sure that I place the encode wheel to zero degree and the shutter window was centered to the mount/telescope position.

 

So, the question is, does it matter being a few degree out when I eventually slew to a target, or I can compensate somehow when setting up the Slave parameters, say on the North offset.

 

 

Any suggestion will be appreciated.

 

 

Carlos


Edited by carlosgib, 07 July 2019 - 04:43 AM.


#2 kathyastro

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Posted 07 July 2019 - 06:17 AM

The first thing to do is to make sure that your mount-dome measurements are accurate.  The software needs to know where the centre of the mount is in relation to the dome.

 

If the measurements are correct and you are still getting an error, you need to see if the error is accumulating.  If it is just 2 degrees out and remains 2 degrees out forever, then just redefine where your zero position is.  If it is 2 degrees out this week, 4 degrees out next week, 6 degrees out the following week, you have a serious problem on your hands.

 

My dome had an accumulating error where it would be half a degree out on every slew.  Half a degree doesn't sound like much, but tracking an object across the zenith could mean 90 dome slews in an hour: an accumulated error of 45 degrees, which would put the slot well away from where the scope was pointing.  An accumulating error could require replacing the entire control system, which I am in the process of doing.



#3 carlosgib

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Posted 07 July 2019 - 03:22 PM

Thanks Kathleen for answering, I still need to test the rotation with a target to check that the 2 degrees are constant, if the degrees does not increase or reduce I will treat this a good, in SGP I can enter a few degrees as allowable error, 2 degree is about 35mm.

 

Thanks again



#4 GeneralT001

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Posted 19 October 2020 - 10:48 PM

Thanks Kathleen for answering, I still need to test the rotation with a target to check that the 2 degrees are constant, if the degrees does not increase or reduce I will treat this a good, in SGP I can enter a few degrees as allowable error, 2 degree is about 35mm.

 

Thanks again

Dis you ever resolve the issue??




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