[evlatests] New ACU Project

[Jim Jackson]

All,

This summer , we released an RFP  to bring an Antenna Control Systems 
Consultant in to work with us on the design of a new ACU for the EVLA 
(and VLBA).  That contract has just been awarded to Gregory 
Maglathlin of Nashua, NH who has over 30 years experience in the 
design of Antenna Control Systems for Space and Defense applications. 
He is currently working on a major upgrade to the 120ft   antenna at 
Haystack. ( I can provide a copy of his resume to anyone who is 
interested)  I'm looking to have Greg spend a week in Socorro in 
early-mid January to get this started.

The current plan is to come up with a control system design based on 
commercial off the shelf hardware and open source software that will 
replace all existing ACU and FRM electronics in the EVLA and VLBA, 
support the existing AZ/EL & FRM motors and drives, support new 
modern AZ/EL & FRM motors and drives should the money become 
available to upgrade them, new encoders and modern safety requirements.

I would like have an internal group discussion sometime in early - 
mid December of interested parties here in Socorro to discuss ideas, 
specifications, requirements and wish lists for anything we would 
want a new control system to do, either now or in the future (better 
pointing, faster speeds, higher energy efficiency, etc. - if you can 
think of it, now's the time to mention it). With current economic 
conditions, we are probably only going to get one shot at  upgrading 
our control systems and will need to live with the results for the 
next 20-30 years.

I'll set up a meeting when I return from vacation on the 29th.  In 
the mean time, I wanted to give everyone a heads up so they can be 
thinking about this.

(If I've missed anyone in the distribution for this feel free to 
forward it - I'm hoping "evlatests" gets most everyone else that 
would be interested)

Happy Thanksgiving,
Jim Jackson







At 11:20 AM 11/19/2010, Doug Whiton wrote:
>A modern ACU would have a dramatic improvement in this type of performance.
>
>Doug
>
> >     Ken and I continue our testing with the goal of improving high
> > frequency pointing and efficiency.   One of our tests involves two
> > orthogonal cuts through the beam (to determine its location and
> > characteristics) -- one in azimuth and the other in elevation.   There
> > is a marked -- and important -- difference between these.
> >
> >     When stepping in elevation,  the 'settling time' is very fast --
> > amplitudes are stable with 3 or 4 seconds, although a small amplitude
> > oscillation of period 4 to 6 seconds is discernible.  The amplitude of
> > this small oscillation is 1 to 2 arcseconds.
> >
> >     When stepping in azimuth, the behavior is very different.  The
> > response shows a slowly damped oscillation of remarkably large
> > amplitude:  The amplitude corresponds to an overshoot of ~8 arcseconds,
> > the fundamental period of the oscillation is 8 seconds.  Even after 20
> > seconds, the oscillation is still visible in the data.   The damping
> > time is about 10 seconds -- after this length of time, the oscillations
> > are sufficiently small that useful data can be collected.
> >
> >     I presume the origin of this azimuth behavior lies in the servo
> > system.  Certainly the characteristics dictate that we cannot speed up
> > 'referenced pointing' by shortening the stepping time to less than 20
> > seconds.  Reducing the amplitude and period of the azimuth oscillation
> > would certainly be helpful!
> >
> >     I attach two postscript plots to show the effect.  The data are
> > taken at K-band.
> >
> >
> >
> >
> > _______________________________________________
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> > evlatests at listmgr.cv.nrao.edu
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> >
>
>
>--
>Doug Whiton
>National Radio Astronomy Observatory
>Servo/MOS Group Leader
>575-835-7417
>
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