Re: Things that customers do that drive me nuts on CN

Roland Christen

The problem with using the peak value is that is is susceptible to random worst case scenarios: sudden huge spike in seeing, piece of dirt in DEC worm, moth landing on the camera :).
Again, you turn off Dec guiding and just look at the Dec axis peak motions of the star. You eliminate any guider commands and all motor and axis motions. You have only the pure atmospheric movements, the peak value which the star is bobbling around on your guider graph. Set the Min Move to between 60 and 80% of that peak value (minus any large outliers). Drop the aggressiveness down from 100% to between 60 and 80% for starters. Let the Dec axis guide slowly to remove the steady drift, not trying to follow every bobble of the guide star.

RMS and Peak are not related. You can have a 20 arc second peak excursion for a short period of time and the RMS value may be the same as five excursions of 3 arc seconds in the same time period. Look up "root mean square" and how that is calculated from peak value and time period. RMS is normally used in electrical power transmission to calculate the heating value of a particular waveform.

Rolando

-----Original Message-----
From: stephenjwinston@... [ap-gto]
To: ap-gto
Sent: Tue, Jul 10, 2018 10:01 am
Subject: Re: [ap-gto] Re: Things that customers do that drive me nuts on CN

Hi Roland,

I just responded to Bill on this before seeing your post.

RMS is a measure of error from the predicted data, which in this case is the error with respect to straight line tracking, I would have thought? So isn't the RMS primarily determined by the variation ("error") caused seeing?  But maybe I'm misunderstanding how PHD2 calculates this value.

Anyway, the max DEC error I see with guiding turned off can vary greatly.  I just uploaded a screen grab from last night's GA calibration run.  The reported peak DEC error was 3.71 arc-s or 1.25 px.  I think using that as the DEC MinMo would be overly pessimistic.

The problem with using the peak value is that is is susceptible to random worst case scenarios: sudden huge spike in seeing, piece of dirt in DEC worm, moth landing on the camera :).  It doesn't necessarily give a good ide a of what the average seeing or tracking will be.

Steve

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