AD7147 for Water Level Sensing

Hi Siva, The AD7174 is not designed for this application and there are more suitable devices for water level sensing as described in this article
https://www.analog.com/en/analog-dialogue/articles/liquid-level-sensing-using-cdcs.html

The AD7147 is a self capacitance (grounded sensor) measurement device. Mutual capacitance (floating sensor) measurement is more effective for water level measurement as described in the article. The AD7142 is a mutual capacitance measurement equivalent of the AD7147.

Having said that it should work but it is critically dependent on the design of the sensor electrodes, can you provide details of the sensor construction, e.g. the sizes of the aluminum plates, the distance between them, how they are positioned relative to each other, how the water interacts with the plates.

As a quick check, If you gradually bring your finger closer to the CIN0 plate do you see an increasing result ?

Regards,

Maurice.

Hi Maurice,

Thank you for your information.

I share our sensor details below,

Material: Aluminum Plate
Shape: Rectangle
Width: 2mm
Height: 4cm
Distance b/w them: 1cm

Q: how they are positioned relative to each other
A: The two plates are placed beside each other.

Q: how the water interacts with the plates?
A: The sensor is placed inside a plastic container covered with a thin plastic cover. The water we pour inside the container will have contact with that plastic cover.

The left side plate is connected to the ground and the right side plate is connected to the CIN0.

Q: If you gradually bring your finger closer to the CIN0 plate do you see an increasing result?
A: When the sensor is placed inside the container, the result doesn't change until my finger partially touches the sensor. Once my finger touches the sensor the result increases non-linearly.

Hi Siva, If the plates were made wider and placed closer together you should get improved sensitivity and a more linear response. with the sensor as it is I think that the response is too small and only responds to large changes in water level.

Hi Maurice,

We have already tried the wider and closer plates,

Material: Aluminum Plate
Shape: Rectangle
Width: 1cm
Height: 9cm
Distance b/w them: 5mm

But the CDC reaches its max value for smaller changes in water level (1.5cm or 2cm of water level) also the change seems to be as same as the sensor mentioned above, but the difference is the change occurred in more minor water level changes. That's why we moved to this sensor.

with the sensor as it is I think that the response is too small and only responds to large changes in water level.

Q: Even though the response is too small and only responds to a large change in water level, why it has to be this level of increase in the result (i.e. more than a 10k difference), does it is the expected response?

We also tried different sensors with different sizes. All the sensor's results stayed near the mid-value (32,767) for some water levels and then jumped to 46,420. The only difference is, the change in CDC results occurs at different water levels.

Q: why it has to be a similar type of CDC response for different sensor plates?

Hi Siva, If you shift the initial value away from mid point, to 50k for example do you see the same situation ?

Hi Maurice,

Sorry for the late reply.

We ain't test that.
Right now we were working on some other projects, so will test that later and let you know the result.

Thank you.