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| Oscilloscope mains probing |
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| GeorgeTsak:
Hello, EEVblog! I have seen many videos / posts including Dave's video on how not to explode your oscilloscope, saying that the oscilloscope's ground is directly connected to the earth ground and that if you connect the ground lead of the probe in the wrong place a short circuit could occur. They also stated that if you wish to measure a device that is earth grounded you should use an isolation transformer, differential probes or if you are more extreme remove the ground pin from the oscilloscope power cable. My question is, since the oscilloscope is earth ground referenced shouldn't you be able to measure mains by just connecting the positive lead of the probe, leaving the ground lead disconnected without any issue? |
| Richard Crowley:
In theory, yes. Making many assumptions, some of which could be hazardous or fatal depending on conditions and factors that may not be obvious to the inexperienced. You could start by asking WHY you want to measure the power mains, and WHAT you expect to see, and HOW you intend to protect yourself and your test gear from the many hazards. |
| GeorgeTsak:
Thank you for your reply! I do not wish to measure mains at all. I was just curious. |
| tggzzz:
--- Quote from: Richard Crowley on September 11, 2019, 12:58:22 pm ---In theory, yes. Making many assumptions, some of which could be hazardous or fatal depending on conditions and factors that may not be obvious to the inexperienced. You could start by asking WHY you want to measure the power mains, and WHAT you expect to see, and HOW you intend to protect yourself and your test gear from the many hazards. --- End quote --- Precisely. The OP could start by looking at the praxis/safety references at https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/ If the OP is ever tempted to disconnect a protective mains earth, have a look at https://www.eevblog.com/forum/projects/isolation-transformer-for-scope/msg2259465/#msg2259465 |
| Gyro:
--- Quote from: GeorgeTsak on September 11, 2019, 01:04:48 pm ---I do not wish to measure mains at all. I was just curious. --- End quote --- Sadly, that is how a lot of new scopes meet their doom. Beginners (not making any assumptions about your level of experience) buy them and realize that the only signal sources they have are the probe cal output and the mains. It's a really good time to breadboard a 555 timer oscillator or an opamp sinewave oscillator to experiment with. Kudos for being honest about your reason and for asking before you try probing the mains. :-+ |
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