Products > Test Equipment
Floating Scopes
WastelandTek:
so let me get this straight
say I have a 5A21N here, I can hook a conventional probe to each input and then probe 2 points in a circuit that are BOTH above (or below) ground potential safely right?
I have the diff amp, so I don't need the diff probe, or am I missing something?
alm:
Yes, assuming that you observe the limits of both the probes and the plugin. And be careful where, and if, you connect the ground leads.
Keep in mind that attenuating probes, e.g. 1:10 or 1:100 probes, may degrade your common mode rejection ratio (CMRR). A high CMRR relies on a close matching of the attenuation of both channels. If your probes have a 1% mismatch in attenuation ratio, your CMRR will be limited to 100:1. Tektronix made some probes with adjustable DC attenuation for that (like the P6055 and P6009), so you could adjust one probe to match the other. Obviously 1x probes will have a very good match in attenuation ;).
HighVoltage:
For the young players:
When I was 16 years old, I had to learn a rule when measuring any dangerous voltage:
"Keep one hand in the pocket"
Do I follow this rule these days?
No!
But it made me aware of what I am doing every time I measure dangerous voltage, especially high voltage to 80.000 Volt.
tronde:
--- Quote from: serggio on June 26, 2017, 07:51:41 pm ---
TN-C, for example, obsolete for now, but still present at many many countries, predominantly at old buildings, do not propose any third PE (ground) conductors in mains outlet.
All that you have - this is Phase conductor and Neutral (PEN) conductor in your mains. In this case your modern scope will be always float!
--- End quote ---
Yes, you can find som older buildings wired that way in Europe. But, you should not find any legally installed wall socket with a disconnected earth contact. If you wire with two wires, the earth contact in the socket should be connected to the neutral wire/contact (the PEN wire you mention) within the socket. This is not the same as floating the scope, because PE will always be connected to neutral at least one place in the building if you have any kind of a TN-system.
As I mentioned in my previous post, you can find some places using wall sockets without any earth contact. They have been used regardless of the distribution system, and you will of course not have any PE connected to your scope so it will be floating in that case.
PartialDischarge:
--- Quote from: JohnG on June 27, 2017, 01:14:12 pm ---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?
--- End quote ---
Exactly. My scenario is pretty specific, but I'd say it is accurate and shows the Vgs gate charge 'waveform', Also the peak Vgs which was what worried me, is within calculations and specs.
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