[evlatests] December Engineering/Tests Meeting

Terry Cotter tcotter at nrao.edu
Mon Dec 19 18:19:49 EST 2016 

The specification supplied to us for our part by Dow-Key states 
1,000,000 cycles min. Our part has been customized from their standard 
part by adding the circular connector on the back. The Dow-Key part that 
ours is built from on their website states Mechanical Life(cold switch) 
100,000. I do not know if this is a change from 2011 or if it has always 
been this way and I do not know if they did something to our switches to 
make the better. Chip Scott is the person who evaluated these switches.

Terry

On 12/19/2016 4:03 PM, Bryan Butler wrote:
>
> agreed here - i didn't think 1000000 cycles was the MTBF, but rather the
> expected lifetime per unit.
>
> would be good to know which it is.
>
>
>
> Ephraim Ford wrote on 12/19/16 16:01 :
>> 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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