Adding probe to a circuit affects it

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kjetilf
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Joined: Thu Feb 25, 2016 10:56 pm

Adding probe to a circuit affects it

Post by 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 :-).

Martyn
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Location: St. Neots

Re: Adding probe to a circuit affects it

Post by 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
Technical Support Manager

kjetilf
Newbie
Posts: 0
Joined: Thu Feb 25, 2016 10:56 pm

Re: Adding probe to a circuit affects it

Post by kjetilf » Fri Feb 26, 2016 10:56 am

Hi

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

Kjetil

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