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Sherlock Ohms

The Lightning Came With a Crash

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Rob Spiegel
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Watch out for Mother Nature
Rob Spiegel   10/4/2013 7:16:01 AM
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This is great. The system fails because Mother Nature was not taken into account. Bravo for the engineer who could see through the technology to a natural solution.

far911
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Re: Watch out for Mother Nature
far911   10/5/2013 1:15:34 PM
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TRUE

Battar
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And nobody noticed...
Battar   10/6/2013 10:21:27 AM
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You're telling me that for 3 months nobody noticed that the system "occaisionally crashed" only during a thunderstorm? And nobody noticed a link between "thunderstorm" and "electrical interference" ? There are only two possible explanations for this:

1) Your software guys were pure software, with no knowledge of hardware (not credible)  or

2) that your installation (like the PDP-11/VAX computer rooms I worked in when I wore a uniform) were situated underground.

Nancy Golden
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Re: And nobody noticed...
Nancy Golden   10/6/2013 4:41:58 PM
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As amazing as it sounds that they couldn't see the connection between a thunderstorm and a system crash...those software guys simply could not think outside of the box. They were so busy defending the performance of the system that they couldn't see the obvious. Sometimes people get tunnel vision and need someone from the outside to point things out. 

Mydesign
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Natural considerations
Mydesign   10/7/2013 5:44:46 AM
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1 saves
Jim, interesting experience. I think normally we won't account such natural things during the system design phase. This explains the necessity for considering such natural things.

btlbcc
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Gold
Florida Lightning
btlbcc   10/7/2013 2:19:19 PM
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I read somewhere that Florida is the most lightning-active area in the USA.  I suppose one can get used to anything...  And apparently the computer crash didn't happen with every thunder crash, so it's understandable why the software guys didn't catch it as being a hardware problem.

Brooks Lyman

William K.
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Re: And nobody noticed...
William K.   10/7/2013 5:59:12 PM
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"Just one liitle error". That sort of problem can bring huge systems to s crashing stop, with far worse results than in this posting.

But what I didn't get was if the ignoring the receiver input was a hardware function not included, or a software function not switched on.

jgundie
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Iron
Re: And nobody noticed...
jgundie   10/7/2013 8:16:04 PM
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Nancy you made me think more about the problem. What's not said is that the data transmission often had errors caused by the lightning and CRC testing would catch them. Also I would guesstimate there could be over thousand hits a day ( a "single" bolt of lightning probably created multiple data hits). At 1ms per data packet there were almost 100 million packets/day so a 1000 packets a day being thrown out was not a flag of concern but an indication the system was working correctly.

With a 100 nS window of opportunity in a 1 ms time window that suggest probably only 1 out of 10000 hits could corrupt the CRC protection (note the lightning had to hit only the last 100 ns not before; if it hit before it would be detected and thrown out by the CRC detection).  That in turn suggests that only once every 10 to 100 days there would be a crash. As I recall a three week interval between crashes was an interval was once spoken too.  Also Florida was considered the lightning capital of the world (Congo beats them out) with Tampa recording 21,000 cloud-to-ground (Ju 93); cloud-to-cloud probably affected our system too.  For a perspective a bolt of lightning can exceed 50 KA and have rates of change of 40 KA/s.  The source voltage behind this gets very high.

jgundie
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Iron
Re: And nobody noticed...
jgundie   10/7/2013 8:21:40 PM
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It was a hardware function that was not implimented correctly.  I suspected the person who designed the circuit did the test verification that showed it worked correctly (:|) repeating a conceptual error.  The system had been well tested in CA without many problems.

jgundie
User Rank
Iron
Re: Natural considerations
jgundie   10/7/2013 8:37:53 PM
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The system design spec was good and in this respect if it had been met there would not have been a problem.  The spec specified the digital data receiver inhibit the data input during the interrupt interval.  The hardware implimentation somehow missed doing what was specified although I believe the designer thought he/she? had met the reguirement.

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