"Greg Mayman" bravely wrote to "Mike Ross" (05 Apr 04  10:04:00)
 --- on the heady topic of "{at}%^{at}#$%^ VEROBOARD"

 -=> Mike Ross said to Greg Mayman
 -=> about "{at}%^{at}#$%^ VEROBOARD" on 03-31-04  08:41.....
 MR> I think you have a misplaced trust in electro-mechanical devices.

 GM> 1. Electro-mechanical switching has been in use for over 100
 GM> years, during which time the techniques of designing,
 GM> building, using and checking them have been continually
 GM> improved.

 GM> 2. Electromechanical switching systems are open for visual
 GM> inspection, and virtually all defects can be observed and
 GM> corrected before they affect the electrical switching. For
 GM> this reason, they are always given a regular maintenance
 GM> regime.

 GM> 3. Contacts on relays in high reliability systems are always
 GM> duplicated, and in addition they are designed to have a
 GM> sliding, selfcleaning action which tends to remove dirt, oxide
 GM> etc. When one of the multiple contacts becomes so contaminated
 GM> that it fails to work, the others will carry the load until a
 GM> visual inspection of the contact shows up the fault and the
 GM> contact can be manually cleaned.

 GM> 4. Solidstate switches either work or they don't. There is no
 GM> simple method of detecting whether one is about to fail, until
 GM> it actually does fail.

 GM> What else is there to say?

Thank you for listing a thoroughly concise description of failure
mechanisms and strategies used to compensate for them. But there are
basic holes, i.e. in one case, just because one doubles the number of
contacts does not guarantee the circuit will be close every time. For
example there may occur a large mechanical shock which momentarily
jars the relay, disabling it. As for the argument of experience,
elevators, cars, and planes also have been designed for 100 years and
still breakdown to cause fatalities. An electronic switch by contrast
can operate, a relay equivalent of billions of years in only a single
second. If you don't trust it, I don't think you are being objective.

 Mike
 ****

... # <--- electrocuted tribble
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