Using liquid for the pressure media in the MPXV7002?

[krassnokutskikr]

Hi there, I recently bought three MPXV7002 pressure sensors as part of anemometer kits from hobbyking. I would like to use these sensors to measure the velocity (wash) off various propeller (impeller) designs in a water tank. The frequency response and pressure range of these pressure sensors is a good match for this application. However, I would like to fill the sensor's cavities with water so that I can eliminate any comprehensibility/lag effects associated with air.

I was thinking of injecting distilled water (or deionised water) into the cavities with a small hypodermic needle. Will this mess up the sensors readings? Alternatively, I can use oil as it is a perfect insulator, but I am not sure what type of oil to use so that it does not degrade the sensors internal components?

Anyone who can lend some useful information in this regard would be most appreciated...

Kind regards

Alex.

[david_diaz · Accepted solution]

Hello Alex,

Freescale's standard pressure sensor products are qualified to be used at dry air, only.

For the use of pressure sensors in any other environments than dry air will require additional precautions and protection of the sensing element inside the pressure sensor:

Freescale's silicon pressure sensors are not compatible with oil, gas, petrol and water or water vapors, or chemicals.

After some working hours, maybe days the device would fail. The strain gauge and the electronic circuitry for calibration and compensati  on are protected by a nitride layer but the aluminum bonding pads which provide electrical connections between the leadframe and the gauge are not protected, in order to make the bonding feasible.

The complete die is also protected with a silicone gel. This gel is not fully hermetic, although we use much better gel for our newer types of pressure sensors, water or any other fluid can penetrate the gel and can reach the die.

Possible solutions to use our sensors in applications with other media than dry air:

Usually 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 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. Please let me know if you need detailed information.

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

Have a great day.

David Diaz.

[krassnokutskikr]

Thank you for the detailed response David.

It most certainly is helpful!

Kind regards

Alex.