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Registered Member #690
Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616
This is probably something common/simple, but google and the instruction manual turn up nothing...
I just got my first scope the other day, and I am trying to use it to test some simple things that I know work, just to get the hang of using the scope (my interrupter, ZVS, etc.). But whenever the probe tip touches anything metal, or even my body, the scope reads a 60hz sine wave that varies in amplitude depending on the size of the object it touches.
It screws up the triggering system, making it fire with the 60hz wave causing other waveforms to travel.
I know it has something to do with the mains, and I've been playing around with the controls for about 2 hours now, with no luck. How do I get rid of this?
Registered Member #690
Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616
Sorry for the double post, but I think I found the problem. I was doing some continuity testing on the probes with a dmm, and it read 8-9 MOhm from probe tip to core of the cable, but could not find a ground path.
I tried the ground connection on the front of the scope, and the problem is eliminated. Now to see if I can reconnect te probe grounds to the cable...
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
This is quite common, the 50/60Hz EM field is emitted from various electronic devices and it gets induced in conducive objects. If you touch the probe, the voltage induced in your body is capacitively coupled to ground and this is why you can see it on the scope (which is also grounded). This is also why speakers connected to audio amp hum as you touch the audio input of the amp.
Registered Member #514
Joined: Sun Feb 11 2007, 12:27AM
Location: Somewhere in Pirkanmaa, Finland
Posts: 295
This is normal. If you just touch the tip of the probe and leave the ground clip unconnected that is what you will see. Once you connect the ground clip the 60Hz waveform goes away.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Hmmmmm, from what you said it sounds like the ground clip on your scope probe is busted. The ground wire often breaks where it fastens onto the probe. We had some in the lab at work that had broken and been repaired about a dozen times.
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Stupid scope question
