capacitive Sensor Circuit Design

[salkaoud]

Hello folks, 

I am implementing a circuit including capacitive sensor that measure a displacement using NI Multisim. the circuit design starting from the sensor part, charge integrator, then AM Demodulation. 

My concern is that how can I make the capacitance increase independently by using variable capacitance and how can I measure the difference of the capacitance value, how can I show the amplitude difference when the capacitance change with the time.

thank you please tell if you feel I need to improve my circuit.

[azp7]

Hi Salkaoud,

I don't understand completely your doubt about "capacitance increase independently by using variable capacitance and how can I measure the difference of the capacitance value".

So, to answer you

1- Can you check this?

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000000P7H0SAK&l=en-US

2- If you want to measure capacitance, you can use an oscillator and measure the frequency. The frequency will change according to the capacitance and it will be easy to measure and calculate. Something as

Just to give you an example. In the same way, you can use an LM555.

[salkaoud]

thank you azp7 for your reply,

for the circuit which you attached where should I connect it in my circuit same thing with LM555

another problem I am facing and looking for a solution I tried to increase the capacitance value manually then get the output voltage I got a non-linear increasing slope of the capacitance Vs the output voltage. Now to calibrate my mechanical side I need a linear order for less error and more accurate result. do you have a way such a filter to overcome this problem your help is highly appreciated

thank you,

the result of the excel sheet is attached.