WATER LEVEL measurement MP3V5050DP

[artem74]

Hi!

I just want to measure water level sensor in tank with water using mp3v5050 pressure sensor. Before i do it i have made a simle test equipment from tube diameter 32 mm and in the botom of it i made a think copper and silicone tube output to sensor. Because sensor is upper lower level of water in tube every time present air bulb. I fill my tube with water (app 1liter). The sensitivity is really awesome. The voltmeter from sensor sense 1 mililiter of water! But i have a trouble. The voltage out from sensor every day go down. First measure is - 0.745V,   1st day - 0.738V........6 day 0.705V. And this is not evaporation water.  I make a mark on water level and it does not change. I have now ideas what is it. Please give some advice about this situation. My schema of test equipment:   

[reyes]

Hi,

The output voltage on the MP3V5050 is ratiometric, this means that output voltage of the sensor is directly affected by the voltage supply. Make sure the input supply voltage is constant. Also make sure that that you properly installed the power supply decoupling and output filtering capacitors as shown in Figure 5 of the datasheet: https://www.nxp.com/docs/en/data-sheet/MP3V5050.pdf

Another possible cause is the pressure connected on port P2 of the MP3V5050DP, if I understand correctly, you are using the differential (two ported) version of the sensor, and you are only using Port P1 to measure the water level, while port P2 is unconnected, is my understanding correct?

If it is correct, the local atmospheric pressure can be changing causing a change in the reference of the pressure measurement, which cause a shift on the output voltage of the sensor.

Have a great day,
Jose

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[artem74]

Hi, thank you, Alberto for responce. Yes i just connect to port P1 and port P2 opened to atmosphere. I suppouse that atmosperic pressure can not changing output voltage, because it apply to water tank too.  Water tank is opened to atmospere .  I have capacitors on power supply.  I not give power all time to system. I power-on system after few minutes check voltage and power-off system.  And do that once a day and voltage every day changing in few percent per day.

[reyes]

Hi Artem,

Thanks for the clarification.

Just to make sure, please confirm that the input voltage is exactly the same all days. This is important for your system since the output voltage is ratiometric from the input voltage, if there is a small drop on the input voltage, the output voltage would be affected. For example, if you are using a battery in your system to supply the pressure sensor, even if you only turn on your system once a day, there would be a small battery drain that could cause the voltage drop you are seen on the output of the sensor.

Have a great day,
Jose

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[artem74]

Ok! I just monitor power supply and output of sensor. and share results. I power my sensor from power supply dc -12V and after decrease power to 3V using dc-dc converter LM2596 chip. 

[reyes]

Hi Artem,

Thanks for share the results, then if the power supply of the sensor comes from a 3V dc-dc converter, I can assume that it is a clean and stable 3.0V voltage signal, right?

Can you confirm if the air gap inside the tube is not changing (probably due to temperature changes), or somehow decreasing overtime?

Have you tested your setup in different sensors? Is this same problem affecting all your sensors?

[artem74]

Hi, Jose,

yes the power supply is 2,975 voltage and it stable. How i can control the air gap? The tube from copper and i cant monitor air gap in them. I test only one sensor. I solder all connections now without connectors to exlude bad contacts in connectors. I will  go to vacation to 3 weeks and after i come back and will continue testing.

This is real picture of my test equipment.

[reyes]

Hi Artem,

Thanks for checking the voltage supply.

In this case, it would be important to check if the air gap has no decreased, this would tell us if the air is scaping trough the liquid, or that there is a very small leakage trough the tubes connections.

Have a great day,
Jose

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