19:25 If that actually cause the computer to reboot, that is indeed very nasty. USB ports are usually fused and/or current limited. I believe they even have to be according to the USB specification.
I did hear before that over current protection occurs by rebooting your PC ...
A little off-topic maybe.
Is it best to ground the scope, or having it floating (use a wall-plug without ground) when measuring or cars/engine-management systems?It doesn't really matter normally,as far as the car is concerned, (BUT see the final sentence!!),because it is standing on four big black insulators,so the car"earth" is not at the same potential as the mains earth!
If you have other stuff connected to the car which causes the car body/chassis/engine block to be at mains earth potential,you have to be careful not to get your earth clip on the wrong spot.
If the latter is not the case,all the voltages in the car,including the few high ones are only with respect to the car body/chassis.etc.
That said,I must repeat what I said in another thread,"There is no real reason to put the earth lead on anywhere else but a point connected to the body of the car."
If you put the earth lead on say,a +12volt point,& your 'scope was sitting on a car seat,& thus insulated from car "earth",all would be well,but if you did the same with the 'scope's metalwork contacting the bodywork,there would be big "zap",& you could damage your probe,your 'scope,or your car.
If you again insulated the 'scope,& placed the earth clip on one of the high voltage points in the car,you would elevate the instrument's
metalwork to that voltage,& perhaps damage yourself!
Your Oscilloscope mains earth would not protect you in this case,because,as I said in the first sentence,the car"earth" is not at the same potential as the mains earth!
To answer your question:DO NOT remove the mains earth from the Oscilloscope,as if an electrical fault occurred inside the 'scope,causing external metalwork to be live,& if the 'scope is sitting on a metal part of the car it would elevate the whole car to mains voltage,so everyone working on the car would be at risk.
A little off-topic maybe.
Is it best to ground the scope, or having it floating (use a wall-plug without ground) when measuring or cars/engine-management systems?It doesn't really matter normally,as far as the car is concerned, (BUT see the final sentence!!),because it is standing on four big black insulators,so the car"earth" is not at the same potential as the mains earth!
If you have other stuff connected to the car which causes the car body/chassis/engine block to be at mains earth potential,you have to be careful not to get your earth clip on the wrong spot.
If the latter is not the case,all the voltages in the car,including the few high ones are only with respect to the car body/chassis.etc.
That said,I must repeat what I said in another thread,"There is no real reason to put the earth lead on anywhere else but a point connected to the body of the car."
If you put the earth lead on say,a +12volt point,& your 'scope was sitting on a car seat,& thus insulated from car "earth",all would be well,but if you did the same with the 'scope's metalwork contacting the bodywork,there would be big "zap",& you could damage your probe,your 'scope,or your car.
If you again insulated the 'scope,& placed the earth clip on one of the high voltage points in the car,you would elevate the instrument's
metalwork to that voltage,& perhaps damage yourself!
Your Oscilloscope mains earth would not protect you in this case,because,as I said in the first sentence,the car"earth" is not at the same potential as the mains earth!
To answer your question:DO NOT remove the mains earth from the Oscilloscope,as if an electrical fault occurred inside the 'scope,causing external metalwork to be live,& if the 'scope is sitting on a metal part of the car it would elevate the whole car to mains voltage,so everyone working on the car would be at risk.
I pretty much agree with everything vk6zgo says here except "There is no real reason to put the earth lead on anywhere else but a point connected to the body of the car." Well we do not know what kind of car cs.dk are working on or what systems it contain, or what kind of measurements he wants to do, but I definitely agree with the last sentence never just disconnect the earth lead, if you feel the need to isolate the scope always use a proper isolating transformer.
Safest is powered off and plug pulled out of the wall on both. If the modem has a metal case then add an external wire to earth, probably via a mains plug earth pin with the wire in the cable grip properly. otherwise you need to strip the cable insulation off somewhere along the cable and earth the shield exposed there, then tape it up again ( no soldering or you melt the inner wires) and wire to earth.
If you own the house drill through the wall and have an earth rod outside the room deep in ground with a 4mm conductor to the inside and bond all ground wires from equipment to it.
Safest is powered off and plug pulled out of the wall on both. If the modem has a metal case then add an external wire to earth, probably via a mains plug earth pin with the wire in the cable grip properly. otherwise you need to strip the cable insulation off somewhere along the cable and earth the shield exposed there, then tape it up again ( no soldering or you melt the inner wires) and wire to earth.
If you own the house drill through the wall and have an earth rod outside the room deep in ground with a 4mm conductor to the inside and bond all ground wires from equipment to it.hmm i guess i gonna buy a new pc psu if the damn thing is plugged in the whole pc case floats at half mains voltage according to the meter the tv and the coax from the optic fibre modem has no problem, the cheap chinese usb 3 hub shield floats too, however everything has a perfect connection to earth, i guess i should call the pwer utility company to check their wiring outside the house and the earth connection, as far as i know the neutral and earth have to be connected before the electricity meter, but i cant check that too unless i void the seal then a huge fine will come soon
Safest is powered off and plug pulled out of the wall on both. If the modem has a metal case then add an external wire to earth, probably via a mains plug earth pin with the wire in the cable grip properly. otherwise you need to strip the cable insulation off somewhere along the cable and earth the shield exposed there, then tape it up again ( no soldering or you melt the inner wires) and wire to earth.
If you own the house drill through the wall and have an earth rod outside the room deep in ground with a 4mm conductor to the inside and bond all ground wires from equipment to it.hmm i guess i gonna buy a new pc psu if the damn thing is plugged in the whole pc case floats at half mains voltage according to the meter the tv and the coax from the optic fibre modem has no problem, the cheap chinese usb 3 hub shield floats too, however everything has a perfect connection to earth, i guess i should call the pwer utility company to check their wiring outside the house and the earth connection, as far as i know the neutral and earth have to be connected before the electricity meter, but i cant check that too unless i void the seal then a huge fine will come soon
If it were properly earthed, the case would not be floating. There's a fault in either your PSU, your house wiring, or your electricity supply, and it's a potentially fatal one no matter where it is. If it's in the latter, you'll have to get it dealt with by the utility, for the former two, you can fix it yourself, you just need to find it.
A bit after 20:0 I think I did actually hear slight static in the audio.