Static Groundwater Measurement

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Static Groundwater Measurement

In the old days of ground water measurement, one used a conductivity switch on 
a measured steel or plastic flat cable, hanged in a borehole, which emitted an 
acoustic signal when the switch hit the water.
This way the groundwater level was measured.

Ground Water Measurement with Autonomous Level Dataloggers

Nowadays these measurements can be made automatically with KELLER’s DCX22 
and DCX22AA i level probes. 
The DCX22 (AA) are autonomous level dataloggers build up of a level sensor,
a memory with microprocessor and a battery.
They are programmed in advance to perform a measurement (for example every 6 hours),
store this measurement in the memory and go back into sleeping mode. 
The sleeping mode allows for a battery lifetime of up to 10 years. 
Programming and readout of the data is done via a K114A USB cable and 
KELLER’s logger 5.2 Windows-based software, running on a laptop or PC.
Have a look at the first graphic.

DCX22(AA) dataloggers can only measure the water column (E) above the diaphragm 
of the sensor. However, most geohydrologists are interested in the distance from the top
of the borehole till the actual water level in the borehole. 
If you look at the second graphic this way of measuring becomes clear. 
Converting the water column to the “depth to water” is pretty simple.
In the datalogger the Total installation depth (B) is programmed as a passive parameter. 
When the measured water column is deducted from the installation depth, 
the “depth to water” value (F) remains. 

The calculation is therefore B-E = F. 



One very important thing is barometric compensation. When a level sensor is placed in 
a fluid, it measures the fluid column + the air column, which rests on the water.
If no correction is made, the measured value would not be correct as 1mbar equals 1cm 
of water. Thus the barometric pressure must be deducted from the hydrostatic pressure.

There are several ways to do this. The most applied method with conventional level sensors 
is the use of a capillar, which is a tube in the level sensor’s cable so the air pressure can
“push back” on the reverse side of the diaphragm.
This mechanical air pressure compensation has one risk, which is the chance of condensation in the tube, causing damage to the level sensor.

Another way is the use of a second pressure sensor to measure only the air pressure. 
When the signals of the level sensor and the air pressure (aka baro sensor) are deducted 
from each other, the pure water column remains.

The difference between the DCX22 and the DCX22AA is the integrated barometric 
compensation in the DCX22AA, which has a second (barometric) pressure sensor in the 
battery pot, which is in the head of the borehole. 
The DCX22AA can store both hydrostatic, barometric and the barometric compensated 
water levels.

The DCX22 however always needs a separate barometric data logger to collect the air 
pressure.



There is one condition for the use of KELLER’s DCX22AA: the barometric pressure
sensor must not be flooded. Otherwise a barometric measurement cannot be made.
KELLER’s modular software allows to use both DCX22 and DCX22AA in a measuring 
network, as the DCX22AA’s barometric pressure can also be used to barometrically
compensate the DCX22’s or a flooded DCX22AA’s hydrostatic pressure.

Used KELLER Products
Direct product links

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