Products > Test Equipment
Floating Scopes
PartialDischarge:
I'll add more fuel to the fire. I can't recommend anyone doing this, but I do it cause I know exactly what I'm doing so please don't waste your time critizing me, ok fellas?.
Just floated my Micsig tablet scope to 620V to measure the Vgs of a switching mosfet. Of course I did set the scope vert and horiz before energizing the circuit and I didn't touch the screen afterwards. Also, the scope was placed in a wooden surface and the probe cable didn't go near metallic areas.
tautech:
--- Quote from: MasterTech on June 26, 2017, 08:29:32 pm ---I'll add more fuel to the fire. I can't recommend anyone doing this, but I do it cause I know exactly what I'm doing so please don't waste your time critizing me, ok fellas?.
--- End quote ---
Right. ::)
--- Quote ---Just floated my Micsig tablet scope to 620V to measure the Vgs of a switching mosfet. Of course I did set the scope vert and horiz before energizing the circuit and I didn't touch the screen afterwards. Also, the scope was placed in a wooden surface and the probe cable didn't go near metallic areas.
--- End quote ---
BUT......by virtue of your tablet scope is not mains ground referenced you haven't floated it at all. :P
Vtile:
First of all I do want to say that high voltages, high current or high energy work with live or powered, but disconnected device under test is something that doesn't belong to hobbyist of young age or hobbyist of high age, but low experience (including lack of understanding of theory) nor with educated person without knowledge of what he or she is doing.
Someone did claim my wording about differential probes are not reasonable. It were, as the response did give more specific information of the type of "usually safe" differential probes. The CAT IV text in the faceplate of the instrument doesn't mean that it really fullfills the requirement (ie. with all the counterfeit product floating in the markets).
Now I have one extra question that also haven't discussed and also is a trap for anyone who doesn't think. I (and I assume many hobbyist that shouldn't do high energy work ) do have one of those handy USB scopes, well it is isolated and floating (with random electrical and mechanical values) when I attach it to my battery powered laptop running charger disconnected and no other equipment connected. Again the same hazard is there the metal parts of the USB scope and propably also on the laptop (through USB shielding wire) just became potentially life threatening to touch.
There is so many traps in this area of electronics and electrical work in general.
PS. Also your ESD cover/mat on the workbench is grounded through random impedance.
PPS. The water circulating radiator under your workbench where you rest your feets seeking a warmth is also propably a directly grounded.. What a nice electrocution chair there. ;)
Specmaster:
The way I look at this is that it does not matter if your scope is battery powered in other words a true portable, floated, isolated or double insulated and the same thing applies the DUT unless battery powered, there are many ways that you can still receive a fatal electric shock. Fact is that all things electrical demand respect and due care and diligence and in our game, especially if you're in the repair game, then live working is unavoidable so common sense must prevail.
In the real world, we would all love to have the very best and finest of equipment, especially if cost was not a factor but sadly it so often is so we each and everyone of us has to weigh up the risk with everything we do in life and the question of safety in the work area / bench is no different. If you don't feel confident working on live equipment, or if uncertain about the suitability of a piece of test equipment etc, then don't do it.
JohnG:
--- Quote from: MasterTech on June 26, 2017, 08:29:32 pm ---Just floated my Micsig tablet scope to 620V to measure the Vgs of a switching mosfet. Of course I did set the scope vert and horiz before energizing the circuit and I didn't touch the screen afterwards. Also, the scope was placed in a wooden surface and the probe cable didn't go near metallic areas.
--- End quote ---
I have to ask: Were you measuring Vgs of a high side MOSFET in a half-bridge, where the common mode voltage is a giant square wave or similar? Did you get a decent waveform? Is it believable? If so, could you send me a picture of it? 100 MHz is likely too slow for me, but I have only been able to do what I want with a borrowed Tek IsoVu (which works very well for what it does).
John
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