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 ...