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FDC2214EVM: Need help to calculate water level from capacitance values from FDC2214- for single ended configuration

sanket kaulkar21
Prodigy 40 points
Part Number: FDC2214EVM
Other Parts Discussed in Thread: FDC2214

We are using FDC2214 EVM for measuring water level in a plastic container. Also the sensor PCB we used was TIDA00317: we used ;one channel per level sensor, ref air sensor and ref liquid sensor.The shield pins were not used as FDC2214 does not have active shield signals. The set up image shown will reveal this.

When we calculated water level as per the equation given,

level = href {(Clevel - Clevel0)/(Crl-Cre)}

the last column of the table shows the calculated water level in cm.

we are not able to calculate exact water level.

can you please look into the readings and suggest improvements so that we can measure exact water level.

 Capacitance in pF
Actual water level  liquid sensor/Ch1 Ref liquid/CH2 Ref air/Ch 3 Calculated water level in cm
0cm 27.27 24.19 27.4 34.83074766
1cm 27.39 24.27 27.44 35.04615142
2cm 27.5 24.3 27.47 35.15615142
3cm 27.61 24.31 27.5 35.21815047
4cm 27.74 24.31 27.53 35.27726708
5cm 27.84 24.31 27.56 35.30769231
6cm 27.93 24.31 27.58 35.35201835
7cm 28.05 24.31 27.61 35.40454545
8cm 28.13 24.32 27.63 35.46232628
9cm 28.17 24.32 27.65 35.45828829
10cm 28.2 24.32 27.7 35.38047337
  • 0
    Prodigy 100 points
    Hello,

    Could you give an example of the values that you placed into the equation?

    A couple quick notes that should be helpful:

    It seems quite strange that the air reference would have a higher capacitance than the liquid reference, you may want to get baseline readings with no liquid in the container to cancel out capacitance from the system, like parasitic capacitance from the wires. Most of the capacitance your FDC2214 is reading isn't actually from the water or the air in your container.

    Also, it seems that your air/system reference is increasing as the volume increases. Are you running exposed wires up to the Reference Sensor at the top? You may want to shield these (like with grounded Coax cables) to prevent this from happening.

    Best,

    Steve
  • 0
    TI__Genius 11340 points

    Hi Sanket,

    I agree with Steven. It is quite strange that your ref air reading is nearly as high as that of the liquid sensor. Could you provide the exact equation and values you used in the calculation? It would be nice if you could provide a full system setup of your system.

    Also, as Steven has mentioned, you should consider shielding the wires if you haven't done so.

    Best,

    Jiashow