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FDC2114EVM: Variation there is when measuring the capacitance of the same capacitor with the FDC2114EVM

Conor
Guru 12115 points
Part Number: FDC2114EVM

Tool/software:

Hi,

Is there any information on how much variation there is when measuring the capacitance of the same capacitor with the FDC2114EVM?
The values ​​of 10 to 20 pF capacitors from other companies vary by about ±20%, so I'm wondering about the accuracy of the FDC2114EVM.

Thanks,

Conor

  • 0
    TI__Mastermind 40295 points

    Conor,

    Our capacitive sensing devices are better at measuring a change in capacitance, as opposed to an absolute capacitance (like a capacitance meter).
    Measuring a capacitance change is easier because it has more relaxed requirements, like calibration, accounting for shifts in environmental factors, etc.
    We don't have any data to offer on the accuracy or variability of a fixed capacitance since that is not the intended application.

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Guru 12115 points

    Hi John,

    Thank you for your answer.

    I understand that when evaluating capacitance with the FDC series, the data is displayed as a number, but is it possible to see the change in capacitance due to differences in conditions or samples from that number?

    Also, could you please tell me, to the extent that you can, how the FDC series is used to measure relative capacitance?

    Thanks,

    Conor

  • 0 in reply to Conor
    TI__Mastermind 40295 points

    Conor,

    You can compute the capacitance of the sensor by first using equation (8) in the data sheet to calculate the sensor frequency from the output data and device settings, and then calculate the capacitance using the relationship fsensor = 1/(2πsqrt(LC)) where L is the known, on-board inductance. 
    Repeat the calculations for the second position of the target for the new capacitance, and take the difference between the two measurements to get the ΔC.

    For the second question, I'm not sure what you mean by "relative capacitance".

    Regards,
    John