# MPX5050GP ( reading kPa  )

Question asked by Tom Balon on Aug 3, 2017
Latest reply on Aug 17, 2017 by Dario Arias

I'm using an MXP505GP pressure sensor to measure dry air pressure. I have the sensor connected to a regulated 5V supply bypassed with a 1uF ceramic at the sensor input. The output pin is connected via a 750 ohm and 0.33uf

filter as per AN1646.  This is connected to my HP meter to test. The power supply is well regulated 5V 1.5A output.

The sensor outputs a 0.2V with no pressure applied as expected from the datasheet.

I applied various pressure using a water column and measured the voltage on the output of the MXP5050GP.

I'm using the transfer function from the data sheet Vout = 5 .13( P x 0.018 + 0.04 ) (  Vcc = 5.13V )

When I plot the values, they are indeed linear, but the pressure (kPa) using the formula seems way off.

If I apply 6 kPa , I get 0.583 volts output, which using the formula indicates about 4 kPa !

Pressure   |   MPX5050 Reading (using formula)

1 kPa           0.58 kPa   0.259V on Meter

2 kPa           1.32 kPa   0.327V

3 kPa           1.93 kPa   0.383V

3.74 kPa      2.43 kPa   0.430V

5.98 kPa      4.09 kPa   0.583V

12.95 kPa    8.88 kPa   1.02 V

To generate the pressure, I am using a column of water. The MXP5050 is connected to a 12 foot section of

1/4" hose which is then submerged into the column of water. To generate a pressure of 2 kPa, I submerge

the end of the tube into the column so that it extends 8 inches below the surface.

Using the formula, I should get 2 kpa, but instead I read only 1.32. At 24 inches ( a pressure of ~ 6 kPa ) it

only reads 4 kPa and is off by 2 kPa !

I must be missing something here ...

Tom