On Sun, 14 Nov 2010 21:22:33 -0600, Jeffrey Angus
wrote:
On 11/14/2010 9:02 PM, Phil Allison wrote:
Only a COMPLETE IDIOT does what you did.
Along with several idiots at Xerox.
While i was working on a switching power supply, we had reason
to measure the input (live) AC line. Tectronix to the rescue.
Apparently they knew there were a few insane people that would
want to float a scope for live AC line measurements and they had
a special isolation box that the scope plugged into for just that
occasion.
Of course, some fool removed it while we were at lunch.
Ya know, it's amazing the fwipzzzt noise the ground lead on an
expensive scope probe makes when it goes up in flames when you
turn the power on.
Jeff
Nicely done. I usually had a sign hanging on the test mess during
lunch. Something like "Touch anything and you'll die". However,
ty-wrapping the power cords to both the instrument and the power strip
worked somewhat better. I also placed mouse traps in strategic
locations until my boss demanded that I stop (after one got him).
So, why didn't you use two probes, with the scope set to differential?
To get the phase, you would need a 4 trace scope, but those are common
enough. I believe that differential is also the recommended method as
it keeps the scope case at ground level and takes care of the common
mode noise on the line. The isolation xformer method puts one side of
the power line on the case of the instrument, which is not pleasant if
you touch both the instrument case and a nearby ground.
Remember.... you have but one life to give to your profession.
Incidentally, I always kept my old broken scope probes. The
intermittent probes were especially prized. I would destroy one about
every 2 months. I would mark them with a tiny red nail polish dot,
and leave them connected in a conspicuous location, while I hid my
working scope probes. When they would predictably disappear, I would
just smile. I also had a #2 Phillips screwdriver with a self
stripping plastic handle. I think it was borrowed (stolen) at least 3
times, and then returned. I still have it somewhere.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558