Simple answer?
My digital o-scope tops out at 20V.
If I want to measure AC ripple on a 400-sh VDC power supply, will the o-scope (in AC mode) simply "ignore" the DC and measure the AC ripple - or will the 400VDC fry my o-scope anyway?
My gut says it'll fry the o-scope.
My digital o-scope tops out at 20V.
If I want to measure AC ripple on a 400-sh VDC power supply, will the o-scope (in AC mode) simply "ignore" the DC and measure the AC ripple - or will the 400VDC fry my o-scope anyway?
My gut says it'll fry the o-scope.
Depends on the scope, it should have a maximum DC input voltage rating specified. This would be
the rating of the input blocking capacitor in AC mode. What is the brand and model of the scope?
You can also use your own 600VDC blocking capacitor of adequate uF rating.
the rating of the input blocking capacitor in AC mode. What is the brand and model of the scope?
You can also use your own 600VDC blocking capacitor of adequate uF rating.
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depends, on the voltage rating of the input capacitor the leads etc. My HP and tektronic leads are good for 400volts DC I have 1 600 volt probe. What do the specs say on your scope? You can always make a 10-1 or 100-1 divider. ie 9Meg and 1 Meg resistors or 9.9Meg and 100k resistors. The resistor value depends on the input resistance of your scope.
OK it is safe to assume my scope is not even close to capable. It would likely be a health hazard (very briefly) if connected to 400V.
Sure, it is basically disposable, but why be reckless with it.
Thanks everyone.
Sure, it is basically disposable, but why be reckless with it.
Thanks everyone.
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Is it 20volts per division or 20 volts max input? There is a big difference. If it's 20 volts per division and you have 8 divisions then the max is 160 volts. If it has a 1 Meg ohm input Z, common for scopes, then get a 600 volt 10 to 1 probe. If it's 20 volts max input with a 1 Meg ohm input Z, then get a hv 100 to 1 probe.
As was asked before what make and model.
As was asked before what make and model.
Thanks again everyone. The simple answer in my specific case is "no". I don't want to waste any more of your time on this.
Even in AC coupling, the input circuit will see 400V for a short moment, when you touch the circuit with the probe. It is because the input coupling capacitor is initially empty, consequently both sides are at the same voltage. That is both sides of the capacitor jump to 400V at the moment you touch the circuit with the probe. Then gradually the capacitor will charge up, and the other side (facing the input amplifier) will settle to zero volts DC. Usually there is some protection buit-in, but better to stay at the safe side.
Yup, it will if you use a x1 probe!
You need a reputable 100:1 high voltage scope probe, and then you won't see much due to the attenuation.
Alternatively make a test fixture using a suitably rated capacitor driving a load resistor to ground - only
connect the scope-probe after powering up once the cap has charged?
You can add a series resistor and clamp to help protect from transients for a more robust fixture.
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