FDC2214：LIQUID LEVEL DETECTION

Hi Wenhan,

can you show a schematic and a photo of the PCB and test setup?

Kai

Hi Wenhan,

Unfortunately, this is not how the FDC2214 device should be used for liquid level sensing. Please refer to the document https://www.ti.com/lit/pdf/snoa925 

are attached outside of the container. 

https://www.ti.com/product/FDC1004?keyMatch=FDC1004&tisearch=Search-EN-everything&usecase=GPN

Regards

Sharath.

why? 

I used this method to measure the change of capacitance with water level. Why can't this method be used? Is the measurement accuracy not enough? If there is a short circuit, if the capacitance can not be measured, it will not have any impact on the system.

Hi,

"I used this method to measure the change of capacitance with water level"

How did you measure the capacitance here? Unfortunately, this setup doesn't work with FDC2214 devices. Please see the documentation to understand the principle and make the necessary changes to your setup.

Regards

Sharath.

Thank you for your reply. In this way, I attach the conductive wire to the detection plate at both ends of the capacitor, and when the level changes, the detected capacitance value changes. So if can't do this, give some reasons. 

I just want to know the shortcomings of doing so.

The document you gave I read and will refer to it.

But in my practical application, it is better to put the detection plate in the water.

Hi Wenhan,

again, can you show a schematic and photos of the PCB and test setup?

Kai

Hi Wenhan,

The FDC2214 is not suitable for measuring liquid level sensing when the sensor is directly in touch with water. The working principle of the liquid level sensing involves measuring the fringing capacitance between the primary LEVEL electrode (CINx) and a ground (GND) electrode in the parallel fingers topology. The fringing capacitance becomes a function of the dielectric variation in the x-axis direction. 

Regards

Sharath.

Sorry. I still wonder why the sensor is directly in touch with the water is not good. Please give more reasons. I have noticed the TI solution of liquid level detection, but actually, I have measured the capacitance variation with the liquid level variation in this method.

Hi Wenhan,

because of ion conductivity direct contact to the water might erode the biasing of inputs of FDC2214.

Kai

Do you mean that the detection end of fdc2214 may be corroded due to the conductivity of the liquid?

But in fact, I used insulating tape to deal with the connection between two wires and water, which would not happen.

Hi Wenhan,

insulation tape does not provide 100% isolation. So you might suffer from leakage currents.

Also, with only two simple wires your capacitance might be too small.

Kai