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FDC2214EVM: Capacitance over Frequency

Philipp Koneczny
Prodigy 10 points
Part Number: FDC2214EVM
Other Parts Discussed in Thread: FDC2214

Hi,

Im designing a Liquid level sensor and im stuck by verifying my measurements.

I measured 2200 femto Farad capacitance difference between empty and full container with an RLC-Meter at 10kHz excitation Frequency.

When i measure it with the FDC2214EVM i get about 1200 femto Farad difference in single ended configuration and 2600 femto Farad difference in differential sensor configuration.

1. My excitation Frequency of the FDC2214EVM is at about 5,1Mhz. Is the excitation Frequency the reason for the difference in capacitance gain in the single ended configuration?

I think it`s because C=Q/U  and Q=I x t and so i get for higher Frequency`s a smaller capacitance Value.

2. For me it seems that the Differential sensor configuration performs better for my application because i need high sensitivity. Why do i get a higher capacitance difference than with my RLC-Meter? Can i trust this measurements?

Best Regards Phil

  • 0
    TI__Expert 3435 points

    Hi,

    The reported capacitance is nothing but the excitation frequency reported in digital form. Equation 7 of the datasheet explains the relationship between the frequency and the capacitance for a specific L. FDC2214 is not designed for measuring absolute capacitance measurement. It is designed to detect liquid level changes by measuring the relative changes in the capacitance when the level of liquid is changed. The differential sensor will definitely have better sensitivity and we recommend it whenever it is possible in the application.

    Regards

    Sharath