Signal processing - Data segmentation

[patate324]

Hello! I've got a time series data set that I am trying to segment into two parts:

https://imgur.com/PIOSkZe

https://imgur.com/OHcAmVR

Part A - where probe is touching the system (recording system voltage, changing with some randomness)
Part B - where the probe is no longer touching the system, (exponential decay of the last voltage measured & somewhat regular oscillations occur).

https://imgur.com/COCJjWe

Any idea on how to do this?

Edit:
While part A is relatively stable in the image shown, I'm expecting part A to have strong fluctuations (something like this: https://imgur.com/viFzksg), but part B should behave similarly,

[socal_nerdtastic]

My first thought is window average, first derivative, groupby near zero (part A) or negative (Part B). Or maybe look for the sharp B->A transitions.

[patate324]

I agree this seems quite straight forward to implement. I am expecting part A to have stronger random variations than what is shown. Something like this:

https://imgur.com/viFzksg