I am using MPS20N0040D-D  sensor for drowning detection application by attaching a pipe on the nozzle of the sensor. The other end of pipe is submerged in the water. Theoretically, the value of the reading should change as we submerge the pipe in water, but it remains constant value at 148 ( I am using 10 bit adc) . I am using the following circuit for the differential amplification of the data.

This is the image of the sensor

I am using a ATmega32a for ADC purposes. Is there any way in which we can check if the sensor is working or not.

Please help ASAP. Thank you in advance.

The drawing you've posted seem to be from here:

http://langster1980.blogspot.de/2014/11/how-to-use...

In the blog post the user says that the sensor is very difficult to mount, as the key is almost invisible. Did you try to rotate the sensor in the socket or circuit ?

If you connect an voltmeter to the differential outputs and blow/suck the pipe, do you see the voltage changing ?

 Cheers,

 Mircea C.

How far are you immersing the tube in water?   That sensor has a range of around 0 to 35 psi. Your value of 141 counts is roughly 4 psi, which translates to ~ 3 m or 10 ft of depth in water.  

This simple test shown here 

http://langster1980.blogspot.ca/2016/05/calibratin...

should help you determine if your sensor is working. (looks like that circuit does not use differential mode).   You don't even need to wire the sensor to an arduino, just have a look with a voltmenter.

I feel that you may be better off with a more sensitive sensor as I doubt you need to measure up to 35 psi.

Voltmeter.