FDC1004: RE reading lower than RL

Jakub Orzechowski

Part Number: FDC1004

Tool/software:

I have created a simple sensor board to use with the FDC1004. I am not using the evaluation board, just the IC. I am using the sensing method with 3 electrodes (Level, RL, RE). The issue is that the RE electrode gives me a lower reading, than the RL electrode. Can the cause of this issue be my PCB design? I have attached a screenshot of the PCB design to this thread. I can also provide more design files if needed.

4 months ago

0 Eddie LaCost 4 months ago

TI__Mastermind 44060 points

Hi Jakub,

Could you also provide the design files? If you are using Altium, please send the Altium files as we are also using Altium. If not, please provide gerbers or PDFs. Please also include the schematic. Thanks!

0 Jakub Orzechowski 4 months ago in reply to Eddie LaCost

Prodigy 10 points

I am using kicad, so I will send gerbers. I have attached them to the message.

liquid_level_sensor.pdf

/cfs-file/__key/communityserver-discussions-components-files/1023/czujnik_5F00_poziomu_5F00_cieczy.zip

0 Eddie LaCost 4 months ago in reply to Jakub Orzechowski

TI__Mastermind 44060 points

Thanks for the gerbers. Sorry, I have not had a chance to review these yet. I plan to review and provide feedback tomorrow.

0 John Miller - Sensing 4 months ago in reply to Eddie LaCost

TI__Mastermind 40295 points

Jakub,

Thanks for the Gerbers. I'm reviewing them now.

You mentioned the RE electrode is giving a lower reading than the RL electrode.

What exactly are you seeing?

Regards,
John

0 Jakub Orzechowski 4 months ago in reply to John Miller - Sensing

Prodigy 10 points

I am using an STM32 uC to read from the IC. I have 3 measurements configured according to the FDC1004 datasheet. Below I am adding a screenshot of the results. Res_m1 is the result from the level electrode, res_m2 from the RL and res_m3 from the RE. First of all, the readings are not that far apart from eachother, and the res_m3 is lower than res_m2.

0 John Miller - Sensing 4 months ago in reply to Jakub Orzechowski

TI__Mastermind 40295 points

Jakub,

Are you using single-ended, differential, or out-of-phase sensors configurations?

Regards,
John

0 Jakub Orzechowski 3 months ago in reply to John Miller - Sensing

Prodigy 10 points

I am using 3 signle-ended measurements. It is configured according to the point 7.1 of the FDC1004 datasheet.

Best regards

Jakub Orzechowski

0 John Miller - Sensing 3 months ago in reply to Jakub Orzechowski

TI__Mastermind 40295 points

Jakub,

If I understand everything correctly, we might expect RE to be larger when there is no nearby liquid because of the longer trace connecting it to the device pin.

With nearby liquid covering the level and RL sensor, you would expect the RL sensor capacitance to be larger than the RE sensor.

Regards.
John

0 Jakub Orzechowski 3 months ago in reply to John Miller - Sensing

Prodigy 10 points

Okay, that does make sense. When the container with the sensor attached to it is filled with water, the reading is correct and behaves in an expected way. The issue i described appears when the container is filled with printer ink. At this point suddenly the sensor seems to completely stop working properly. I wonder if the issue could be that the ink leaves some residue on the container wall?

Best regards

Jakub

+1 Jakub Orzechowski 3 months ago in reply to John Miller - Sensing

Prodigy 10 points

I think I found the issue. I believe that the sensor does not work with ink due to its much lower dielectric constant. Thanks for all the help.

Best regards

Jakub Orzechowski

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FDC1004: RE reading lower than RL