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PSoC 4 MCU

user_1214886
New Contributor

Hi,

We are using CY8CKIT-22 to develop liquid level sensing for drinking water containers.

We are testing the sample with a bottle in the kit and it works very well. Before we made the next step, we would like to hear your opinion if we can hit any problems with our sensor.

The container is 48 cm high therefore we have design cap sensor 48 cm length with two differential pols. The gerberas are in the attachment. The container wall is 5mm thick.

Thank you for your advice.

Regards,

Blaz Selekar

1 Solution
ShanmathiN_06
Employee

Hi Blaz,

Yes, if you use segmented sensors, then Cp will be less. So, you could use that.

We are planning to use the CY8C4025LQI-S401 how many segments can we read with this MCU?

It is just a pin out limitation. You could use PSoC creator and drag down components in the schematic and check how many pins are available as segments.

For temperature compensation, if possible, you could use a reference sensor that is not subjected to any temperature variations and use that as a reference for the liquid-level sensors.

Please ensure that your SNR might be less since you are using a thick overlay with lesser dielectric constant. You can use firmware filters to reduce noise and increase resolution to increase signal.

Thanks,
Shanmathi

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3 Replies
ShanmathiN_06
Employee

Hi Blaz,

Could you please provide the following information?

1) Is the liquid grounded? Or are there any chances for the liquid to be accidentally grounded?

2) Does the liquid have small connection (capacitance) to ground?

3) Is the liquid conductive?

4) What is the container wall made up of? I assume that is acting as a dielectric, so we would like to know the dielectric constant.

5) Is the accuracy of liquid level detection as per your requirements, while you tested with the bottle?

6) Is there any requirements for temperature compensation?

In general, we recommend CSD + shield enabled, for liquid-level sensing designs.

For differential sensor designs, please refer to https://www.cypress.com/file/218531/download​ (Section 3.6 and 4).

The aspect ratio is recommended to be 8:1.

Since, the sensor height is around 45 cm, Cp might be high for the sensors which would result in reduced sensitivity. So, you could drive the hatch with shield signal to reduce Cp and check the sensor performance.

Thanks,

Shanmathi

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user_1214886
New Contributor

Hi,

Thank you for your reply.

I went trough AN202478 in deep and the only way to do this is with Segmented Sensor. If We will use differential sensor the parasitic capacitance will be too big. (The area of each sensor in the sensor pattern should be less than 3,000 mm2)

My answers are following:

1) Is the liquid grounded? Or are there any chances for the liquid to be accidentally grounded?

I don't think so. The liquid is in LDPE (low-density polyethylene)  tank. The tank is placed on the wooden holder I think in the car.

2) Does the liquid have small connection (capacitance) to ground?

No, I don't think so. The drawing of the tank:the_tank.png

3) Is the liquid conductive?

Yes, it is drinkable water.

4) What is the container wall made up of? I assume that is acting as a dielectric, so we would like to know the dielectric constant.

It is 6 mm LDPE (low-density polyethylene), the dielectric constant is 2.2.

5) Is the accuracy of liquid level detection as per your requirements, while you tested with the bottle?

Yes, it should be because now they have only 0%, 25%, 50% 75% and 100%. If we will implement 12 segments or even more it will be enough.   We are planning to use theCY8C4025LQI-S401 how many segments can we reed with this MCU?

6) Is there any requirements for temperature compensation?

Yes, I think we should because in the car we can have from -30°C to 40°C. Also, we must consider vibrations, but the measurement will never be made when the car is driving. 

Thanks for the feedback.

Regards,

Blaz

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ShanmathiN_06
Employee

Hi Blaz,

Yes, if you use segmented sensors, then Cp will be less. So, you could use that.

We are planning to use the CY8C4025LQI-S401 how many segments can we read with this MCU?

It is just a pin out limitation. You could use PSoC creator and drag down components in the schematic and check how many pins are available as segments.

For temperature compensation, if possible, you could use a reference sensor that is not subjected to any temperature variations and use that as a reference for the liquid-level sensors.

Please ensure that your SNR might be less since you are using a thick overlay with lesser dielectric constant. You can use firmware filters to reduce noise and increase resolution to increase signal.

Thanks,
Shanmathi

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