MPXV7002GP accuracy at the same pressure

Question asked by Toni Benitez on Jul 14, 2016
Latest reply on Jul 17, 2016 by Toni Benitez

Hi. I am designing a pressure control system with 10 MPXV7002GP sensors. In the design of the PCB where the sensors are placed I have followed the instructions on the datasheet (3 On-Chip Temperature Compensation, Calibration and Signal Conditioning).  I am converting the analog signal with a controller with 10bits ADC so I have  ( 0- 5V  --> 0-1023 bits )

Following the datasheet, I have applied this criteria to scale:

0.5 V  --> -2000 Pa  --> 102.3 bits

2.5 V -->         0 Pa  --> 511.5 bits

4.5 V -->   2000 Pa  -->  920.7 bits

And finally I have implemented the auto zero, taking atmospheric pressures every second during 60 seconds to find the average. Then I substract this average in every reading.

I know that with 10bits ADC I can only note changes in pressure of 5 Pa.

I am testing the sensors at atmospheric pressure. The steps are:

1- Start and apply auto zero

2- Every 30 seconds take the atmosferic pressure.

3- During 1 hour I save the lowest and highest pressures.

4- Save the difference between the lowest and highest pressures.

My question are:

Is it normal that at atmospheric pressure I have differences between 10 Pa to 30 Pa between the lowest and highest pressures?

Normally the pressures are never 0 Pa but  -1, 4, -6.....jumping every 30 seconds normally by 5 Pa.

Some real example:

 PRESSUREDIFFERENCE 10:4512:15Diff P P min P max 14:0517:36Diff P P min P max 17:4519:03Diff P P min P max SENSOR P00 10 -6 4 10 -6 4 25 -6 19 SENSOR P01 15 -6 9 15 -7 8 15 -1 14 SENSOR P02 10 -5 5 20 -10 10 24 -5 19 SENSOR P03 10 -4 6 19 -9 10 24 -4 20 SENSOR P04 15 -5 10 15 -7 8 34 -8 26 SENSOR P05 10 -4 6 15 -11 4 24 -6 18 SENSOR P06 10 -5 5 14 -7 7 14 -1 13 SENSOR P07 10 -4 6 15 -11 4 25 -6 19 SENSOR P08 20 -16 4 39 -12 27 14 -4 10 SENSOR P09 14 -5 9 10 -6 4 29 -6 23

Is this normal?

Have I followed the correct steps?

Thanks