Michael Tope wrote:
> jimlux wrote:
>
>> Kipton Moravec wrote:
>>
>>
>>> On Fri, 2009-01-30 at 06:53 -0800, jimlux wrote:
>>>
>>>
>>>> donovanf@starpower.net wrote:
>>>>
>>>>
>>>>> This discussion of relay reliability and switching speed is
>>>>> irrelevant for a relays in a phased array that should never be hot
>>>>> switched.
>>>>>
>>>>>
>>>> The reliability issues in the Tyco ap note aren't tied to whether the
>>>> contacts are carrying current.
>>>>
>>>>
>>>>
>>> Carrying current IS the whole issue. If they were not carrying current
>>> then it does not matter how fast the contacts close or open.
>>>
>>> The goal of the applications note was to minimize the contact arcing,
>>> which increases contact life or reliability. It is described in the
>>> second paragraph of the second column of the first page.
>>>
>>> http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3311.pdf
>>>
>>> You do not have arcing if there is no current. So if there is no current
>>> then contact speed is not an issue.
>>>
>>>
>>>
>>>
>> I think they're talking about the "control contacts", while the life
>> issue is the "controlled relay". i.e. the residual flux making the
>> relay sticky, etc.
>>
>>
>>
>>
> Jim,
>
> Did you actually read the app. note? It very clearly indicates that the
> reliability issue is due to contact welding caused when high levels of
> DC current are interrupted in the normally open contacts. It also goes
> on to say:
>
> This is a great app. note, but my reading is that the particular
> circumstances for which it applies aren't those found in a RF phased
> array application.
>
>
Indeed.
I'm looking for a copy of another relay life apnote that talks about
the contact life issue in lightly loaded situations (the RF array) where
they address the close/open speed (and whether DC current through the
contacts makes any difference). I can't remember the details, but I
think it also depends on the contact plating material (and the design of
the contacts).
I might also be thinking of the reed relay situation, where residual
magnetism is of more concern, but I doubt anyone is using reed relays
for a phased array (although.. if they work for a QSK T/R switch, they
should also work for switching antennas).
Time to drag out all the references and update my rfrelay webpage.
I suppose the take home message is that for low rel, low duty cycle, we
can probably do whatever seems to work, but if you have a high rel, high
duty cycle application, it's probably worth talking to the relay
manufacturer about ALL the details.
jim
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