Intermittent problem? No problem!

[jcarmody]

Just wait until it becomes permanent. 

My operators were complaining that an ATE was occasionally turning off, immediately and with no warning.  It never happened in my presence and I couldn't figure out why.  My only thought was that the PXI controller was overheating, but I couldn'd find any evidence of that.

It happened very frequently this weekend and I came in this morning to a dead ATE.  A few minutes of troubleshooting led me to suspect the switch on the power conditioner.  This is what I found:

The stationary and moveable contacts were complete burned away.  I replaced the switch and the problem went away.

[AnalogKid2DigitalMan]

Defective or under rated switch or is there a high inrush current when the switch is turned on?

I had a complaint that one of my laser automation stations would not power up sometimes. There are 5 high power brushless DC servo amps (= very high inrush current when powered on) in the system that were fed by a dedicated line in the system.

Someone decided to plug the line into the rack's surge strip instead. Flip the switch on and you get a loud popping sound in addition to a flash of light.

-Ak2DM

[jcarmody]

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@AnalogKid2DigitalMan wrote:

Defective or under rated switch or is there a high inrush current when the switch is turned on?

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I don't think there's a high inrush.  Maybe the blower?  The ATE has been in production for five years, so it doesn't feel very underrated.  I'll go with defective.

[altenbach]

Sometimes the spring or screw contacts get weak over time, and if you try to draw significant current, things start arching. Almost looks like the rivet separated.

I would have thought that an olfactometric analysis should have given an early warning. 🙂 Maybe that switch box was well sealed, though.

[jcarmody]

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@altenbach wrote:

[...] Almost looks like the rivet separated.

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That's what happened, but I didn't find it in the switch.  Maybe it was consumed.

Last year there was a reported "zapping" sound when the ATE shut down.  It occurred over a weekend so I wasn't there.  The operators restarted the ATE and everything was fine.  I asked the plant electricians later and nothing untoward was discovered.  Nothing smelled, except the situation.