[evlatests] December Engineering/Tests Meeting

[Alan Erickson]

If we view the EVLA as a testing facility for RF switches, we've had 308 
devices under test for (conservatively) 58k cycles with 24 failures, 
from which we can calculate the observed MTBF as (308/24) * 58k = 750k 
operations. Given likely errors in the number of wear-producing 
operations, I consider this comfortably within the manufacturer's 1000k 
MTBF -- quite so, as this data encompasses the infant-mortality stage. 
Although we should ensure that our sparing and maintenance costs are 
accurately forecast, I don't see this as an alarming failure rate.

Please holler if you think I'm off in left field.For those who would 
like to see a short refresher on MTBF, Vicor has a digestible summary 
(MTBF on p. 7):

    (note: direct pdf 
link)http://www.vicorpower.com/documents/quality/Rel_MTBF.pdf


On 12/19/2016 12:40 PM, Bryan Butler wrote:
>
> found a bug.  conclusion still the same.
>
>
>       time period          SBs   hours  band switches  no band switch
> ------------------------  -----  -----  ------------- --------------
> 2016 nov 1 - 2016 nov 30    266    560       1290           12605
> 2015 dec 1 - 2016 dec 1    3214   5912      13902          170043
> 2012 dec 1 - 2016 dec 1   12126  24250      58227          684849
>
>
>
> Bryan Butler wrote on 12/19/16 12:00 :
>>
>> some data on how many band switches we make.
>>
>> numbers are approximate because i'm not including test time (though we
>> don't often switch bands during testing), and i don't catch quite
>> *everything* that is science observing, but they are first order
>> probably about right.  i did three scales of length of time as a sanity
>> check that the values scale about right, which they do.
>>
>> over the month of november 2016 we had ~570 hours of science observing
>> time in 274 SBs on the VLA.  during that time there were ~1942 true band
>> switches, and ~12400 scans that didn't switch bands.  i give "~" values
>> because i'm assuming that the first scan of an SB always switches bands,
>> which isn't necessarily true, but i figured was the most conservative,
>> and it will catch some of the missed test time band switches.
>>
>> over the year from december 1 2015 to december 1 2016, we had ~5912
>> hours of science observing time in 3214 SBs on the VLA.  during that
>> time there were ~20800 true band switches, and ~163000 scans that didn't
>> switch bands.
>>
>> over the four years from december 1 2012 to december 1 2016, we had
>> ~24250 hours of science observing time in 12126 SBs on the VLA. during
>> that time there were ~86300 true band switches, and ~656780 scans that
>> didn't switch bands.
>>
>> steve tells me that hichem says that if there is no change in bands at a
>> scan boundary, the switch is not told to do anything.  if that is really
>> the case, then these switches have not gone through anything even close
>> to 1000000 cycles.  if, however, for some reason they actually are
>> cycling at such a scan boundary, then we're getting to about 3/4 
>> lifetime.
>>
>>     -bryan
>>
>>
>> Rick Perley wrote on 12/14/16 15:24 :
>>>     All:
>>>
>>>     We have three items (so far) for discussion.  There's time for more
>>> -- let me know if you have something to show/tell/discuss.
>>>
>>>     1) Steve:         RF Switches.
>>>
>>
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