MP3V5004GP for measuring tank water level

[rkris]

Hi,

We are trying to use the MP3V5004GP  to build a wireless sensor node which will measure water level in a tank (depth 1 meter).  The problem is that the sensor output starts dropping even though the water  level is constant.  We  are using Tygon Lab Tubing (Non-DEHP, 3/32"ID X 5/32"OD).  The node electronics (including the MP3V5004GP with one end of the tube attached to it's port) is outside the tank and the other end of the tube is at the bottom of the tank. The tube is a pretty tight fit (tube ID is smaller than port diameter) and is not easy to detach from the port but we still see water enter the tube leading to drop in sensor output. I even tried permanently gluing the tube to the sensor port. I recently came  across AN1513 which suggests  using hose clamps to reduce leakage. Can you help me us selecting the right hose and clamp for the MP3V5004GP ? 

Ram

[igadotti]

I am having the same issue, air leaking. Tried to use silicone to seal the hose in the sensor, but no success.

Can you recommend another seal/glue appropriated to the sensor housing material?

I also believe the air might be leaking through the sensor! Is that possible?

[rkris]

Hi David,

I  am still waiting for your response.

Ram

[david_diaz]

Hello Ram,

There are many variables which affect the end performance of the sensor. The main error contributor in such systems are the temperature, and the offset.

Outside this temperature range (below of +10°C, or above +60°C) the output will become less accurate, and you will may see a shift in the offset at the device's output, and following you will see some erratic. This is a known effect with this product. If possible, you may perform an AUTOZERO as much as you can, and also have the value of the temperature for appropriate compensation.

The AUTOZERO is the easiest and most efficient way to annul the offset mentioned, the system stores the offset value and then performs the measurement.

AN1636 - Implementing Auto-Zero for Integrated Pressure Sensors

As additional information, in a water measurement application, a head tube is used. This is simply a piece of tubing between the sensor and the container in which the water level or pressure needs to be measured.

Air is trapped in the tube and this isolates the sensor from the liquid water.

I would like to refer to the following application note that would be worth to be considered in addition to the provided information.

AN3728 - Media Compatibility for IPS PRT Pressure Sensors

I hope this information will be useful for you.

If I misunderstood your question, feel free to let me know.  I will be glad to help.

Have a great day.

David Diaz.

[rkris]

Hi David,

    I am already aware of the issues pointed out by you. I am also using a head tube. Please read my post again.

    My problem is air leaking from the head tube resulting in water entering in the tube leading to loss of pressure.'

    How do I prevent the air from leaking ?

Thanks

Ram

[david_diaz]

Hello Ram,

Please accept my apologies for the delayed response.

In this case, hose clamps are recommended for use with all of the hoses mentioned above. In addition to helping prevent leakage and loosening, hose clamps provide a stronger connection to the sensor port.  Clamps that are recommended for use in applications as described are the Oetiker Two-Ear Clamp, and the Oetiker One-Ear, and Special Clamp from Newage Industries.

Here below are some suppliers of hose tubes, and clamps e.g.:

• Oetiker: http://www.oetiker.com
• Professional Plastics: http://www.professionalplastics.com
• Saint-Gobain Plastics: http://www.tygon.com
• Piedmont Plastics, Inc.: http://www.piedmontplastics.com
• Shin-Etsu Chemical Co., Ltd. in Japan: http://www.sifel.jp 

Standard pressure sensors port options are designed to accept readily available silicone, vinyl, nylon, or polyethylene tubing for the pressure connection. The inside dimension of the tubing selected should provide a snug fit over the port nozzle. Installation and removal of tubing from the port nozzle must be parallel to the nozzle to avoid undue stress which may break the nozzle from the port base.

Following app. note AN936 can be considered for tubing option:

http://www.freescale.com/files/sensors/doc/app_note/AN936.pdf

I hope this information will be useful for you.

If I misunderstood your question, feel free to let me know.  I will be glad to help.

Have a great day.

David Diaz.