Pneumatic Water Level Sensor

– this project is in progress –

– not working yet –

2010 we drilled a well in the backyard for watering our plants. The groundwater level is high but i was interested in the annual high fluctuations and temperature of the groundwater. So the idea was to messure the hight of the water using the pressure wich is needed to press air out a small tube on the ground of the well. There big advantage of this: no electronic parts have to be actual in the water.

Part List

airpump
tube with a plumb (see titel picture)
pressure sensor (currently working with the MPX2050 and MPX5100)
microprozessor to read the sensor and show the values
display
temperatur sensor

First Tests – Reading the Sensor

The well is about 4,6m deep. The pressure rises 0,1 Bar each meter of water. So we have approximately 0,5 Bar at ground of the well. 0,5 Bar = 50 kPa = ca. 5mH2O

That was easy – coming to something difficult: resolution
At the beginning of this project we have to think this part really through as it defines what we want to buy and how we want to solve the tasks we will have to solve. 🙂

If we want to read changes about 1 cm this would be 0,001 Bar = 0,1 kPa. Available pressor sensors can normally measure pressure in 1 kPa steps.

The MPX2050 has a Sensitivity of 0,8 mV/kPa
The MPX5100 has a Sensitivity of 45 mV/kPa

1 kPa = 0,01 Bar = 101,97 mmH20
So it’s not the resolution of different sensors that matters, it’s the resolution of the Analog Digital Converter short ADC or A/C of the Chip we will use.

[most Arduino AVR Boards contain a] …10-bit analog to digital converter. This means that it will map input voltages between 0 and 5 volts into integer values between 0 and 1023. This yields a resolution between readings of: 5 volts / 1024 units or, .0049 volts (4.9 mV) per unit.
www.arduino.cc analogRead()

As the MPX5100 would give us 0,2V to 4,7V in 0,045V steps the MPX5100 would work with the ADC of most Arduino Boards.