If you are measuring the cap voltage with a multimeter, make note of the capacitor discharge and voltage drop due to the multimeters input resistance.
This can be significant for small capacitor values (below a µF).

Oh for my application i will use an ADC afterwards tò read the value

 

Oh for my application i will use an ADC afterwards tò read the value

How will the ADC read the cap value if it's not grounded, but floating at the 3.3V supply voltage?

 

How will the ADC read the cap value if it's not grounded, but floating at the 3.3V supply voltage?

I can use a differential ADC, or u suggest me to use a circuit with 1 grounded plate of the cap?

 

I can use a differential ADC, or u suggest me to use a circuit with 1 grounded plate of the cap?

Depends upon how good the common-mode rejection of the ADC is for a 3.3V common-mode voltage.

 

Depends upon how good the common-mode rejection of the ADC is for a 3.3V common-mode voltage.

ok i understood thanks

 

Regarding cap discharging, here the path is shown. The cap is discharged through p-ch mosfet. The current is limited by Rds of this mosfet that is usually around 10ohm for small signal mosfets. So the initial peak current is about 3V/100=300mA, usually much less since the mosfet isn’t turned on in zero time (in linear region at beginning). Also 100mA countinous current mosfets is able to peak 500mA without any problem.