I want to measure water level (+/- 2 m) in my tank using a pressure sensor MPX5100DP.
I use the schematic of AN1516 (figure 3) with a (air) pipe in water. The pressure in the air pipe is measured by the positive pressure inlet of the MPX5100DP.
When I try to calibrate the sensor (Vs = 5 V) I get a slope of 3,1 mV/cm water level.
If I read the data sheet, every 1kPa of pressure will give 45 mV Vout. But a pressure variation of 1 kPa is caused by a water height of 10 cm! So I must have a slope of 4,5 mV/cm...
How is it possible?