FDC1004QEVM: Liquid detection using just the proximity sensor

Ishan Panchal

Part Number: FDC1004QEVM
Other Parts Discussed in Thread: FDC1004,

Hi There,

I am trying to detect the liquid using the FDC100QEVM. As per reference designs, you guys are using more than one channels so I just wanted to know if it would be feasible with just one channel and GND/SHLD connection.

As of now I am getting minor deflections but they are extremely small.

Please let me know.

over 1 year ago

0 John Miller - Sensing over 1 year ago

TI__Mastermind 40295 points

Ishan,

Just to confirm, you want to use just a single channel for the liquid measurement without a liquid reference sensor and the environment reference sensor?

Regards,
John

0 Ishan Panchal over 1 year ago in reply to John Miller - Sensing

Intellectual 640 points

Hi John,

Yes, Just a single channel. Please note that I just want to detect the liquid threshold, I don't want to measure the liquid levels.

Thanks..!!!

0 John Miller - Sensing over 1 year ago in reply to Ishan Panchal

TI__Mastermind 40295 points

Ishan,

It should be possible to do what you want, but the particulars will depend on the details.
For example, there can be tradeoffs between the sensor size, the sensor-liquid separation distance, the liquid, and the container shape and material.

If you are willing to use a single sensor and an electrode driven by the shield, you may be able to implement the Out-of-Phase Liquid Level Technique, which makes the liquid electrically neutral, and less sensitive to nearby conductive objects.

Noet that the threshold function will need to be implemented in the uC. The FDC1004 doesn't have it built in.

regards,
John

0 Ishan Panchal over 1 year ago in reply to John Miller - Sensing

Intellectual 640 points

Hi John,

Thanks for the inputs..!!!

Instead of container, we have a 10mm diameter plastic tube. Using the EVM, I observed that I am getting deflections on the GUI with the liquid reaching threshold but they are very minute. I just want your guidance on the proximity sensor design to amplify the deflections. As of now I am using the proximity sensor came along with the FDC1004QEVM. Based on the reference guides I also designed some sensors of small size suitable to fit with our application.

0 John Miller - Sensing over 1 year ago in reply to Ishan Panchal

TI__Mastermind 40295 points

Ishan,

I'm guessing the sensors are not getting enough interaction with the liquid in the tube.
That being said, what are the dimensions of the PCB in the image, and the individual sensors on the board?
Would it be possible to provide and image of how the PCB is positioned with respect to the plastic tube?

We will be OOO after noon/CST today, so any responses may be delayed until Monday.

Regards,
John

0 Ishan Panchal over 1 year ago in reply to John Miller - Sensing

Intellectual 640 points

Hi John,

As of now I am using a proximity patch in the top row of above PCB image. The size of the patch is 11x11 mm and the sensor patch overall pcb size is 23.6 x 15 mm. Please see attached layout snap with dimensional details for better understanding.

The PCB is placed parallel to the plastic tube containing sample, please see attached image for same.

One thing to report, the FDC1004QEVM sometimes shows negative capacitance, it doesn't matter if the sensor patch is attached or not, please see attached snap of GUI graph for same. This is the case with both the TI proximity patch and my patch and without any patch. I have ordered some extra chips from TI, please let me know if I need to change the IC.

Thanks..!!!