Re: hot scope leads?

On Fri, 21 Jul 2006 09:43:15 +1000, "Phil Allison" <philallison@xxxxxxxxxx>
wrote:


BobFlintsTone@xxxxxxxxxxxxx

Normally, you DO NOT use a scope to measure AC mains leads, unless you
have a
special attachment to allow it, usually a signal transformer. At work, we
rent a
power analyzer when we want to see the AC.


** That seems over cautious to me - a standard 10:1 probe is well able to
safely cope with 120 / 240 volts AC.

I'm just going with the idea that you don't need a scope to check your AC, you
can use a meter. And if you really want to check the AC, a power analyzer can
tell you wonderful things. You just leave it on for the weekend and it logs all
kinds of events. The last one we rented was worth about $15,000... logs
frequency, harmonics, voltage fluctuation, everything.

Anyway, the problem with a scope is where to put the ground lead! LOL! Of
course, we know it goes on the fat pin...

( I also own a 100:1 probe rated at 1500 volts max - guess what THAT is
for, Bob.)

Gee, Phil, it might come in handy on vacuous equipment... I also have a
current-to-voltage probe, but have never tried it... it's good down to 1ma I
think.

Also, when working with triac and SCR circuits that "chop" the AC supply,
one cannot use a transformer to safety isolate the waveform from the scope
as it may well have a large DC component.

Yes, a transformer isn't a good idea with a switcher anyway, with all those
possible harmonics, you want to look directly.

Transformers are such snobs, don't like DC one bit - they get all snooty
and refuse to pass it and just sit there, fuming at you !


I've seen lots of gear that had a cap in series with the transformer... not sure
that's a good idea either.


....... Phil




.

Relevant Pages

  • Re: HOT keeps breaking down
    ... I do not trust their computers. ... >> I ordered a new LOPT and also two 1506's. ... transformer that drivers the base of the HOT is displayed. ... did not know where to get the mass for the scope, ...
    (sci.electronics.repair)
  • Re: hot scope leads?
    ... have a special attachment to allow it, usually a signal transformer. ... rent a power analyzer when we want to see the AC. ... I'm just going with the idea that you don't need a scope to check your AC, ... Yes, a transformer isn't a good idea with a switcher anyway, ...
    (rec.audio.tubes)
  • Re: Fisher VCR model FVH919 snowy pix.
    ... Now that I've repaired the transformer, ... that it may be a head switching issue. ... He said to use a dual trace ... scope to monitor the preamp output with respect to the PG pulse. ...
    (sci.electronics.repair)
  • Re: WANTED: Vintage Tektronix Equipement
    ... I have a Tektronix CRT and Shield: ... and the power transformer: ... The transformer part# is 120-0575-00. ... I believe they are from a 561 rack mount scope I scrapped for the ...
    (rec.radio.amateur.boatanchors)