How to transform capacity (F) to Voltage (V)?

[mpierettis]

capacity voltage

Hello guys.
Does anyone know how can I transform farads to volts? If I make an RC circuit can I make the galvanometer to capacity-meter?
If not, how else?
I have a capacitive humidity sensor that according to the humidity it changes the capacity. So I want to make a circuit to transform this capacity to voltage.
Please help me.
Thank you a priori.

 

[FoxyRick]

capacity to voltage

Hi,

First, do you have the part number and datasheet for the humidity sensor? They probably have some application notes, and at least the capacitance and amount of change.

The capacitance change you will be measuring is likely to be quite small.

You could use the sensor as the C in a resonant circuit, say a CMOS oscillator. Then measure the frequency of the oscillation, or convert it to a voltage with an chip such as VFC32KP from Texas Instuments.

Temperature stability may be a problem due to the small capacitance change you are looking for.

Here's some links:

http://www.dataweek.co.za/news.asp?pklNewsID=2868&pklIssueID=295&pklCategoryID=45

http://www.capsense.com/capsense-wp.pdf

Cheers,
FoxyRick.

 

[mpierettis]

voltage capacity

Thank you very much.
So, I can not just transform Capacity to Voltage, without using oscillator.

I am thinking of making a capacity-meter so that I can have from capacity straight to voltage.
Do you think this can be done?

Thank you a priori.

Added after 2 minutes:

Also, the capacitive humidity sensor I use is the TI-A of Toplas Engineering company.
I don't have the full data sheet. i don't there is one.
I have some graphs that show the relationship between capacity and RH.

 

[lucbra]

capacity sensor howto

Maybe you can try to put your humidity sensor in a AC wheatstone bridge.

But most of time, the capacitor is put in an RC oscillator

Success

 

[mpierettis]

computation of capacity from voltage

Thanx.
I will try it and let you know.

 

[mpierettis]

capacity to voltage converter

I think I have found the solution. if someone is interesting, can read the following:

**broken link removed**

Added after 41 seconds:

lucbra thank you for the tip

 

[alphi]

capacitive humidity to voltage

you can to find LCR meter manual from agilent web

 

[mpierettis]

capsense.com

Can you please help me with the web address?
I am new here, so I don't quite know all these.
Thank you very much a priori.

 

[venkateshr]

how capacity changes voltage

HI,

There is another posible soln for this.Just use an AC voltage source and form a
capacitance divider with one constant cap and the variable.Take out the voltage.
you can use a dc source also.The voltage varies if the capacitance changes.

Bye

 

[manitooo]

howto humidity

c. dVc
i=--------
dt

where i is the current that pass through the capacitor, C is the value of the capacitor, Vc is the voltage at the capacitor's pads.

Where U use the current Law, you will find a differential equation that you can solve...