concentric capacitive sensor

[preetikarki]

hello,
i am doing a practical on a concentric cylindrical capacitive sensor.it is of very basic type.the capacitance is 150pF.The dielectric medium is kept open( air is taken as dielectric).according to my circuit s requirement i need a capacitive sesor which will charge and discharge.does this concentric capacitive sensor charges?
Secondly when ever i change the dielectric , the capacitance does not vary. why so?is their any special condition to be provided to the sensor in order to get change in the capacitance with respect to the dielectric constant?

 

[FvM]

what is concentric cylindrical capacitive sensor

i need a capacitive sesor

Not clear, what you're asking for. According to your previous posts, you have an electronic circuit. And you apparently have a capacitor ("the capacitance is 150pF").

when ever i change the dielectric , the capacitance does not vary

If you're referring to gases, the variation is actually very small. But the capacitance is proportional to εr anyway.