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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:

PRESSURE

DIFFERENCE

10:45

12:15

Diff P

P min

P max

14:05

17:36

Diff P

P min

P max

17:45

19:03

Diff 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

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