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Joined: Jul 2004
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The old joke goes "A person who speaks 2 languages is bilingual" "A person who speaks 3 or more languages is a polyglot" "A person who only speaks one is an American" (alternately an Englishman)
From what I read all of the original documentation was in Dutch and I found translations into other languages but English seems to be elusive.
Greg Fretwell
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Here's a nice video on Lissajous patterns. Your external X amplifier is useful for studying phase relationships. https://www.youtube.com/watch?v=t6nGiBzGLD8It might remind you of "The Outer Limits". You would use TV Frame triggering and usually - slope to look at composite video signals. Some scopes can select between even and odd fields. Frame rate is almost 30Hz and the color frame rate is almost 15Hz. The stability adjustment on my 15MHz Heathkit scope, had to be adjusted to get a full width horizontal trace. Joe
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Joined: Jul 2004
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I lived in the digital world so we never used the X input. You can plot the 2 outputs from a stereo audio amp to get interesting patterns tho. I knew some guys who rigged an old Heathkit GR25 TV to do it. I also played with doing it with a laser to project on the wall but lasers were tough in those days. (no diodes)
Greg Fretwell
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When I was younger, I didn't have the $$$ for isolation transformers. I knew that the TV had a hot chassis and my scope had a power transformer that would allow it to reference at the TV chassis ground, if I lifted the scope earth ground. So I removed the three of us from proximity to Earth. Not as dramatic as a guy in a Faraday Suit, hopping off a helicopter, to work on 500KV lines, but the same general idea. Joe Really, I removed the scope's and my reference to Earth and the TV chassis shifted us negative WRT Earth.
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I don't see the switch on the PM but our Tektronics scopes had the ability to invert and add channel 2. You could put ch2 on the hot common, invert/add and probe with 1. You then just see the differential signals without a ground reference
Greg Fretwell
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I don't know if I should ask this question here but it is related.
The other day a friend who is renovating a hospital OR theatre was commenting on the voltage found on the isolated or "floating system". It all made sense. He was getting 60V from L1 to ground and 60V Neutral to ground (or I guess you could call it L2).
After our conversation I was thinking about my Hammond 120:120 isolation transformer that I use to energize devices under test with my scope. I plugged it in to a standard wall outlet that measured 123 V. Then I measured the secondary of the Hammond transformer via the standard female cord end. I found approximately 120 V from L1 to Neautral, 72 V from L1 to ground, and 20 V from Neautral to ground. The last two measurements do not add up to 120 V. Where did the other 28 V go?
A malfunction at the junction -------------------------------------- Dwayne
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I was thinking that the hospital system is 3 phase vs my home being single phase and maybe that's a clue as the voltage readings?
A malfunction at the junction -------------------------------------- Dwayne
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Considering that your earth ground is completely separate from the isolated 120V circuit under test, I would not be surprised at practically any readings one might get, and I would not expect the two readings (L1 G and L2 G) to necessarily add up to exactly the L1 L2 voltage (120V). And having L1 G and L2 G appear to split the 120V evenly seems a little suspicious. Could there be some inadvertent coupling going on?
That said remember that by taking measurements, you are in effect making a connection that did not exist before the measuring operation - albeit a very high impedance connection.
Are you taking your readings on an open circuit? Or is there some load? Would it make any difference? I dont know. Try it both ways and see.
I recall in Navy shipboard electrical systems, which are intentionally UNgrounded, you could still get a good jolt by touching a leg of the 120V system and any exposed metal around (i.e. earth ground, so to speak), due I suppose to capacitive coupling.
Working with ungrounded (isolated) circuits can be fascinating definitely a little different. Thx.
There are 10 types of people. Those who know binary, and those who don't.
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Tom
Shinnston, WV USA
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