When to ground probes?

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Joined: Sat Feb 03, 2024 9:21 pm

When to ground probes?

Post by alexa.rts »

I'm new to Picoscope and can't seem to wrap my head around why I sometimes need to ground a probe other times not. I have a Diagnostic tool, which outputs a serial data stream. I plugged the tool into mains, my 2204A into my laptop, and then put the probe onto the data out pin. It showed a weird graph from roughly -12v to +12v even though the pin shouldn't have been live, with no data stream. The same thing happens if I probe the positive of say, a 12v power supply. I would expect to see a flat 0v line from the tool, and a straight 12v line from the power supply.

Yet when I probe the output of a synthesizer, outputting a +-1v sawtooth wave, the scope works as expected.

What's going on here? Why is it I am able to probe my synthesizer and get a waveform, yet probing even just a simple power supply or diagnostic tool gives the same weird waveform of -12v to +12v. When do I need to attach the ground on the probe to the ground of the thing I'm measuring?

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