Measuring Capacitance accurately

[Trishool]

Hi I need to measure capacitance from 300pF to 370pF for a scale of 0 to 10V at the output any circuit Very reliable ,and Linear is most welcome , I will love if based on PIC , 8051 or purely analog but need to be capable of Industrial application.


Thanks Guys
TrIsHooL

 

[flatulent]

bridge

The following bridge circuit is supposed to be linear in impedance. The top of the bridge is driven from an AC signal. The left side has two 370 pF capacitors in the two arms with the bottom arm grounded. The right side has at the top 370 pF and at the bottom your capacitor. The trick is to put an op amp between the junctions on the left and right side of the bridge and the output to the bottom end of the bottom capacitor on the right side. The AC output voltage will be proportional to your sensor capacitor reactance in excess of 370 pF worth. Go from voltage to capacitance in your uP.

One drawback of this circuit is that your sensor capacitor has to be floating and you have to connect to it with short leads.

 

[Trishool]

flatulent , Could you please provide some schematic BTW I am conditioning a Humidity sensor and do not want to use 555 as they have suggested it is some what non linear ,I can take a tolerance of 2% error in the reading .
Thanks
Ts