problem with mpx6115 Pressure sensor

[Sharagim]

Hi,
I am trying to drive a mpx6115A but I have a problem.
When I plug according to typical design in datasheet and connect it to voltmeter I see "3.444 V" when I put something on its surface it wont change ! when I put it outdoor very small change "3.440" ! when I blow very hard I see a little change like going to "3.5 V"
Is this normal ? How can I measure such a small changes with Atxmega ?

 

[keith1200rs]

It is a gas pressure sensor so putting something on its surface won't make any difference. It is not particularly sensitive so you need to use a significant amount of pressure to get a large change to the output voltage.

Keith

 

[Sharagim]

Thx for reply.
I connect it to ADC and I see it is showing 85kPa in room
when I go outdoor I see 86kPa !
Is it correct I mean inside and outside has only 1-2 kPa differential ?

 

[keith1200rs]

Unless you live in a pressurized room I wouldn't expect any difference in the pressure. If you climb up 3000ft I would expect you will see the pressure drop.

Why do you expect air pressure inside and outside to be different?

Keith

 

[Sharagim]

I am trying to find different between outside and inside pressure. inside we use some vacuum to make negative pressure and we want to have airflow from outside to inside.

 

[FvM]

It's a bad idea to measure small pressure differences with an absolute pressure sensor. Instead you'll want to use a difference sensor with the smallest available range and connect it with tubes to inside/outside pressure.

A pressure difference of 1 kPa is very high and won't allow to open a door. I guess you rather see the offset temperature coefficient of the sensor or a similar effect.

 

[Sharagim]

You are right and I see it is not possible to find such a low differential with absolute sensor.
Is there any specific sensor which you think I can achieve this ? freescale has many sensors but I is there any which you have good experience before?

 

[FvM]

I must confess that I don't have experience with Freescale sensors. But it's all about offset and offset drift and respective measurement accuracy. In some cases, it's possible to autozero the sensor (with known zero pressure difference), this will reduce the sensor accuracy requirements considerably.

You should have an idea about expectable pressure difference and required resolution, short- and long-term stability. A simple water filled U-tube manometer can be a perfect instrument if you don't need an electronic measurement, by the way.

 

[Sharagim]

I changed the sensor with mpx5050dp and it solved my problem.
BR,