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FDC Differences of architectures

na na78
Guru 16770 points
Other Parts Discussed in Thread: FDC1004

Hi

We would like to achieve the application such as the following.

The sensor electrodes are dipped into fluid directly.

We are assuming the impedance of the fluid is not to zero (CINx and GND are not shorted).

In the case of using FDC1004, we have following questions.

Questions:

1.Is the measurement result affected by changing target resistance (Rw)?
2.If the answer of Q1 is YES, would it be possible to avoid the affection of target resistance by using the device like FDC2xxx which has narrow band architecture?
Regards
  • 0
    TI__Expert 6480 points
    Hi,

    Yes, the measurement result is affected by the target resistance, Rw. If the time constant of Rw and Cw is on the order of the oscillation frequency, the system will break down. For example, if the sensors are placed in liquid metal, the sensors will be shorted together. If the sensors are placed in air, the sensors will not be shorted together. Therefore, it really depends on the conductivity of your liquid. This concept runs true for both the FDC1004 and FDC2x1x.

    Thanks,
    Rachel