[evlatests] VLA System health

[Emmanuel Momjian]

In addition to what Ken has already listed, note that the stress test
results do not generate any evlatests email traffic, because problems found
through the stress tests get reported by the operators
through maintenance tickets.

Regarding some of the issues that were reported by Rick:

>2) S-band:  No fringes or PDif from ea03 -- presumably, the receiver is
not yet in?

S-band did not have receiver until yesterday. The stress test of last night
shows ea03 working fine.

>    3) C-band:  All antennas fringe.  ea14 gives a negative, or extremely
weak, PDif on all IFs.

ea14 seems to be OK based on the amplitude gain and Tsys values in last
night's test.

>    4) X-band:  No fringes from ea20.  PDif = 0 from ea02 and ea20.
>Both antennas show healthy PSum.  ea14 has very low PDif, but o.k. PSum.

ea20 did not have a receiver for a while. The stress test of last night
shows it has one now, and it is working as expected. Also, its Tsys values
are well behaved. ea02, on the other hand, has extremely bad Tsys values
(reflecting something is wrong in its switched power system).

>    5) Ku-band:  No fringes from ea23, but PSum and PDif both normal.
>ea10 is showing large gain changes from scan to scan (0.7 dB).  All
>others o.k.

ea23 looks OK based on last night's test (it has fringes, but its Tsys is
~50% higher). ea10's issue, whatever it is, cannot be revealed from a
single scan per band stress test.

>    6) K-band:  No fringes from ea23, and PDif is very small (Tsys
>claimed to be 500K).  Ea07 has system temeprature of about 300K.  All
>others o.k.

ea23 and ea07 are OK as seen in last night's test. However, ea28 had a
serious failure (Jerry just reported the problem and its fix)

>    7) Ka-band:  No fringes from ea23, and PDif equal zero on all IFs.
>(Or, Tsys >1000 K).  All others o.k.

This was OK last night.

>    8)  Q-band:  No fringes from ea 23 on IFs B and D (and PDif = 0).
>Fringes seen on IFs A and C.
>                        ea08 gives zero PDif on all IFs.
>                         Very high Tsys (> 200K) on ea 7 and ea18.

While ea18 is OK in last night's test, ea07 has Tsys values that are 2-3
times worse compared to other antennas. ea18 seems to have a serious
problem in its switched power system.

In conclusion, the stress tests do find issues, and the operators take care
of reporting them through maintenance tickets based on the detailed
instructions we have provided them. Also, the design of the stress test (to
have it done within less than 30 minutes, and the fact that it is run one
day a week, and twice on that same day: before and after the maintenance)
does not allow it to reveal every single issue (especially some transient
ones).

Emmanuel



On Wed, Mar 6, 2013 at 10:24 PM, Bryan Butler <bbutler at nrao.edu> wrote:

>
> i'm curious why our normal stress test isn't finding these issues?  i
> thought that was the whole point of those observations.
>
>         -bryan
>
>
> Rick Perley wrote, On 3/6/13 12:00 :
> >      From the short test, preparing for the 'flux densities', I find:
> >
> >      1) L-band:  All antennas o.k., all PDifs are plausible.
> >
> >      2) S-band:  No fringes or PDif from ea03 -- presumably, the receiver
> > is not yet in?  ea06, on IF 'A' gives a sinusoidally varying PDif of 20%
> > amplitude, and 1 minute period.  (It has always done this).
> >
> >      3) C-band:  All antennas fringe.  ea14 gives a negative, or
> > extremely weak, PDif on all IFs.
> >
> >      4) X-band:  No fringes from ea20.  PDif = 0 from ea02 and ea20.
> > Both antennas show healthy PSum.  ea14 has very low PDif, but o.k. PSum.
> >
> >      5) Ku-band:  No fringes from ea23, but PSum and PDif both normal.
> > ea10 is showing large gain changes from scan to scan (0.7 dB).  All
> > others o.k.
> >
> >      6) K-band:  No fringes from ea23, and PDif is very small (Tsys
> > claimed to be 500K).  Ea07 has system temeprature of about 300K.  All
> > others o.k.
> >
> >      7) Ka-band:  No fringes from ea23, and PDif equal zero on all IFs.
> > (Or, Tsys >1000 K).  All others o.k.
> >
> >      8)  Q-band:  No fringes from ea 23 on IFs B and D (and PDif = 0).
> > Fringes seen on IFs A and C.
> >                           ea08 gives zero PDif on all IFs.
> >                           Very high Tsys (> 200K) on ea 7 and ea18.
> >
> >      The lack of fringes from ea23 for Ku, K, Ka and Q band seems to
> > indicate a problem with the UX downconverter
> >
> >
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