Why does the AWG signal drop when I connect the ground lead to 0V in an RC circuit?

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confused.com
Newbie
Posts: 0
Joined: Sun Apr 04, 2021 1:37 pm

Why does the AWG signal drop when I connect the ground lead to 0V in an RC circuit?

I have a simple series RC circuit consisting of 100 ohm resistor and 1uF capacitor. AWG is set to an amplitude of 1.41Vac. If I connect this input signal to my capacitor, then capacitor to resistor and finally resistor to 0V bus on my breadboard and leave the ground reference clip floating, I can see that I have the desired sine wave displayed. As soon as I connect the ground clip to the 0v the signal drops to around 280mV. Does anybody know the reason for this? I have never used an oscilloscope before so please forgive me if I am being slightly dim . I just want to be able to show the input signal and voltage across the capacitor. I am using Picoscope 2204a if this has any significance. Any help would be greatly appreciated as I am pulling my hair out.

bennog
Posts: 83
Joined: Mon Nov 26, 2012 9:16 am
Location: Netherlands

Re: Why does the AWG signal drop when I connect the ground lead to 0V in an RC circuit?

because the output impedance of the sig gen is 600 ohm.

if you want it to be 0 ohm the you need a amplifier between the sig gen and your test setup.

but a amplifier with 0 ohm output blows up if you short circuit it because the current would be infinite.

Benno

JoeD
Newbie
Posts: 0
Joined: Mon Jan 27, 2020 6:10 am

Re: Why does the AWG signal drop when I connect the ground lead to 0V in an RC circuit?

Good Day confused.com,

my guess is that you want to learn more about the typical characteristics of capacitor charging/discharging, and the picoscope's AWG and oscilloscope are excellent tools for studying these basics.
Just change the resistor in your simple circuit to 10k Ohm, go over the simple maths for the new RC constant this 10k Ohm resistor forms with the 1µF cap. and try again.
When you are done with probing and verification of the results, here is an excellent tutorial for you: https://www.youtube.com/watch?v=74fz9iwZ_sM

Have fun!

Cheers,

JoeD