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water tank level sensor (problem)

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Junior Member level 1
Jun 10, 2005
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mpx5050 pressure data

I am trying to measure the water level in an open tank, I do this with a pressure sensor attached on a tube.
The sensor is a "MPXM2102" from freescale

**broken link removed**

The problem is that the measurement is changing alot over time.
This is a log of 53 hours, 1 measurement per minute.
the height you see here is the raw data from the sensor (with opamp), 1 unit is equal to almost 2 mmH2O.
**broken link removed**

I read somewhere on this forum that it is a function of temperature and water pressure that gives you an error.

Can someone explain this, or give a formula so I can calculate this error, and make the measurement more stable.

mpx pressure sensor measure water level

You meassure also the outside airpressure of the atmosphere. (Like a barometer)


You could work around it, just using a diferential-type MPX---- sensor, also provided by Motorola.


Thx OX_Rambo for the site.

I use a differential-type MPX---- sensor.
I use the MPXM2102GS.
So I measure the difference between the airpressure of the atmosphere and the pressure in the tube.

So this can't be the problem.

That why I think it has to be something with the vapor pressure in the tube (like I said in my first post).

I've one of those using MPX5050, and I notice several problem with the device.

1. Wavy water could cause unstable readings
2. The pipe where the port1 of the sensor connected, are not tight enough. So, as you measure, you are losing air pressure.
3. Your signal conditioner might be the problem. Use MPX5100, its stable and no opamp needed.

I've succeed build one of those with level presision of 1mm.

Yes, I also noticed that I have a loss in airpressure over time.

So If I want to use a MPX5100, which would be the best package?
The unibody or small outline, the single ported or dual ported?

The package is not a problem at all my friend. It is just a matter of fit or doesnt fit to your casing or board.
I prefere unibody, (GP) because you can connect the port using an aquarium air pipe. it is fit tight and no glue require. Or you can use the industrial pipe with that size (5/16") that you can get at Ace Hardware.
While at Ace, go to the glue section. Find a bubble-gum-like adhesive, it works good for sealant and doesnt permanently stick.

You could try using a wire sensor with pulsing detections

I am also using MPX5050, and I have several same problem with the device. The tube where the sensor port1 connected, are not strict enough. Therefore, as a measure of you, you are losing air pressure.

Rainwater tanks

Is it required to use pressure sensor? Or you can use other sensor to measure the water level? If so, I would suggest you use the wire sensor.

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