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Adding probe to a circuit affects it

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Adding probe to a circuit affects it

Postby kjetilf » Thu Feb 25, 2016 11:15 pm

Hi

Sorry if my english is a little bad.

I own a Picoscope 5442A and I have a question about probes affecting the circuit. This is probably easy for you too understand and I wonder what it is I am doing wrong.

The test circuit is as following.
oscilloscope_problem.jpg

When I add probe 3(P3) the LED turns off so I can't measure the voltage over the phototransitor.

I have added a video showing the problem.
* https://youtu.be/v5d2WG9ShlM

Sorry if this is a stupid question, but what is it I am doing wrong?

I bought it primarily since it had 4 channels and had PC connectivity as I like to record my findings.

Thanks :-).
kjetilf
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Re: Adding probe to a circuit affects it

Postby Martyn » Fri Feb 26, 2016 7:10 am

These are single ended probes, therefore grounds for all probes must be connected to the same place.

However, inside the scope the grounds for all channels are common, so in reality you only need to connect the ground for one of the probes.
Martyn
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Re: Adding probe to a circuit affects it

Postby kjetilf » Fri Feb 26, 2016 10:56 am

Hi

Thanks, exactly what I needed to know :-).

Kjetil
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