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My oscilloscope's inputs are rated "250V DC + AC peak (10 KHz)." Does this mean it would withstand mains voltage (325V peak) or only 250V DC? I have no plans on doing this any time soon, I am only curious.

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2 Answers 2

up vote 5 down vote accepted

if you add peak voltage to your dc offset, it must be less than 250V.

this was verified with dc and a 10kHz ac wave.

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So practically, it means it can only take in AC with a peak voltage of 250V? –  Thomas O Nov 4 '10 at 15:51
    
yes, but i would stay well below that threshold, i hate buying fuses. –  Kortuk Nov 4 '10 at 15:54
    
I think more than the fuse would blow, it would probably damage the inputs or at least reduce their performance. –  Thomas O Nov 4 '10 at 15:55
    
in my experience a fuse blows, but play it safe. –  Kortuk Nov 4 '10 at 15:56
    
Hmm I haven't seen any fuses on the mainboard of my scope, but they could be hidden under the RF shielding. –  Thomas O Nov 4 '10 at 16:01

AC signals sometimes ride on a DC voltage level. On the scope you may see a sin wave of +60 to - 40 VDC. This is 100 V Ac signal riding on a 10 V DC voltage.

I once worked with a 10 V peak to peak sin and cos signal from a resolver. The reference signal had a 0 V, 400 mV or 800 mV DC level applied to it. A multiplexer would switch between 3 different resolvers based on DC level.

Your scope could handle anything from 250 V peak AC signal to a peak 125 VAC on top of 125 V DC to a pure 250 V DC or any mix as long as the AC Peak signal + the DC level is less then 250 V

For dealing with High voltage signals, use high voltage probes. These typically reduce the signal by a factor of 10 or more. So a 250 VAC signal become a 25 V signal.

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