[evlatests] December Engineering/Tests Meeting

[Ephraim Ford]

Terry, 

Remind me, what is the spec in question when referring to 1,000,000 cycles? I assume it is the expected lifetime (number of cycles, not the MTBF. Those are two different things as Alan alludes to below. Then we'd have to ask the manufacturer if that was mechanical or electrical failure.


-----Original Message-----
From: evlatests [mailto:evlatests-bounces at listmgr.nrao.edu] On Behalf Of Alan Erickson
Sent: Monday, December 19, 2016 3:17 PM
To: evlatests at listmgr.nrao.edu
Subject: Re: [evlatests] December Engineering/Tests Meeting

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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