Re: Remote VCO test/PID servo revistited

[Chris Albertson <chris@topdog.pas1.logicon.com>]

Nicholas Beser wrote:
> 
> I put the results of last nights TASS VCO test on the APL Astronomy club web
> page. Please look at:
> 
> http://www.jhuapl.edu/APLastronomy/tassvcotest.html

Nick I gave it a look.  Do you know more about the Linux
problem?  It could be my fault.  the server tries to do
a fork every time it closes a FITS file.  I have had
no problem running all night but I have only one CCD
head and therefore write only 1/3 as many FITS file per night.
What was the error message? was it logged to one of the
logs in /var/log/...

Also about the reported time.  I have not varified that
the conversion from "ticks" to seconds is correct.  It may
be usefull to time 100 lines with a watch and see if that
adds up the the sum of the 100 scan periods.

Arne's "optimum" times in his table assume a 135mm lens.
You likely do not have three (or even one) 135mm lens.
You will have to derive the focal lengh from the image
scale

The way timming is done is this:
A counter in RT-Linux runs are about 1.1E6 counts per second
(I don't know why the rate is an odd number)  I check the
"row ready" bit 8000 times each second.  When the bit is
on I sample the counter.  So the bit could have been on
for 1/8000 second before I checked it.  This shows up as
jittel in the reported scan interval of about 125us.
Also the whole thing is based on an xtal osilator on the
PCs motherboard.  This thing drifts by about 100 PPM

My plan for automatic VCO setting is to add the scan
interval to the output of the status command.  Then make
the status command work for clients.  Now you can get
the scan interval on demand remotely.  I'll wrire a Perl
script to do a "status" every few minutes and strip the
scan interval from the output and make a correction to
the VCO.  
-- 
--Chris Albertson

  chris@topdog.logicon.com                Voice:  626-351-0089  X127
  Logicon RDA, Pasadena California          Fax:  626-351-0699