FDC2212: temperature stability

user5866401

Part Number: FDC2212

Hello;

An analog switch is connected to calibrate temperature stability.

When switch is off, tank capacitor is measured (100pF %1). The capacitor value is known, so this step is used for temperature stability.

When switch is on Electrot capacitance is measured.

But some thing is wrong and when temperature change, Reading value become faulty.

Any suggestion please.

over 6 years ago

0 Clancy Soehren over 6 years ago

TI__Mastermind 23810 points

So are you saying that the temperature calibration does not appear to be working? Can you share your test data?

The type of capacitor you use is important since many capacitors have significant temperature drift. Are you using C0G capacitors?

0 user5866401 over 6 years ago in reply to Clancy Soehren

Intellectual 430 points

Hello,

I am using C0G capacitors.
temperature calibration does not work.

When I increasse temperature capacitance decrease 248pF to 245pF.
When I meausere with LCR meter on same condition, capacitance does not change.

Best Regards.

0 user5866401 over 6 years ago in reply to user5866401

Intellectual 430 points

Hello;

Cs = 100pF (C0G)

Cx pcb electrot

When analog switch is on, known capacitor 100pF is measured for environmental effect stability.

Cs = 100pF so we may calculate L value to eleminate environmental effect(temperature etc)

After that analog switch is open and we measure Cs + Cx. That value calculate with finding L(inductance value) on first step.

I try to eliminate enviromental effect by this way. When we use to step formula together all constant which are FIN SEL, Fref, L, cancel each other and does not effect result on theoreticaly.

But in the real word it does not work

Best regards

0 user5866401 over 6 years ago in reply to user5866401

Intellectual 430 points

Hello;

How I can solve this problem. In theory all stuff is ok, but it does not work.

do you have any suggestion for my problem?

any help

best regards.

0 Clancy Soehren over 6 years ago in reply to user5866401

TI__Mastermind 23810 points

I looked at your diagram again. Why are you connecting the capacitor between IN1A and IN0A? Normally you would connect it between A and B of the same channel, for instance, IN0A and IN0B.

0 user5866401 over 6 years ago in reply to Clancy Soehren

Intellectual 430 points

Hello,

There is two different capacitor which are measured with two different chanel.

The single mode conversion is used. So there is not any connection error.

Note: I push wrongly "Resolve button"

Best Regards.

0 Clancy Soehren over 6 years ago in reply to user5866401

TI__Mastermind 23810 points

Both the reference frequency (from the internal or external clock), the reference capacitor, and the inductor can vary across temperature. You should be able to see a correlation between your reference measurement and the measurement of your electrodes, but if you are calculating the inductor, then you are not including the impact of fref drift. Is the data consistent if you add in an extra correction factor?

0 user5866401 over 6 years ago in reply to Clancy Soehren

Intellectual 430 points

Hello;
* External clock is used, so its effect can neglect
* Referance capacitor is NPO so its effect can neglect.
* Sensing electrod capacitor is tested on dfferent temperature. It's ok. so its effect can neglect.
* Inductor value is calibrated with switching state, I relate above.

There are no correlation between datas.

Best Regards.

0 Clancy Soehren over 6 years ago in reply to user5866401

TI__Mastermind 23810 points

Please provide your raw test data if you want further debugging help.

Sensors

Sensors forum

FDC2212: temperature stability