Water level sensor 3791/A0 pages

AANDERAA INSTRUMENTS

DATA COLLECTING INSTRUMENTS FOR LAND SEA AND AIR

WATER LEVEL/TEMPERATURE
SENSOR, WLTS. Series 3791 - 3798
These sensors, based on measuring the hydrostatic
pressure and water temperature in a fixed submerged
position, are designed to be used with Aanderaa
Dataloggers and Display Units.
The Water Level Sensor consists of:
• Pressure Sensor with Thermistor
• Cable with Airpipe
• Compensating Unit
The sensors can also be delivered as averaging versions
which is given suffix A in the part number. These versions
will minimize the influence of ripples or waves on the
measurements.

is a sensor with low ageing, small hysteresis and great resistance to mechanical shocks and vibrations. The output
from this sensor is in the VR22 Aanderaa standard. The
sensor has a thermistor measuring the water temperature
and the output is also VR22.

Accurate monitoring of tide and the water level in ports,
coastal and inland waters, rivers and boreholes is of great
importance to many practical projects. This series of water
level or tide monitoring sensor measures the hydrostatic
pressure caused by the head of water above them. The
influence of barometric pressure on the sensors is
compensated for by applying air pressure to one side of the
transducer through an air pipe and compensating unit. The
sensors contain, in addition to the sensing element, a
temperature compensating and a range reducing network.

The averaging versions is designed to monitor water level
or tide where waves and ripples may disturb the measurements. In this version the signal from the sensing element is
sampled every second and a microcontroller calculates the
average value at the end of each measuring cycle. This
continuous averaging of the pressure reduces the
fluctuations caused by ripples and waves. The current
consumption is 1.0 mA continuously and the output is the
SR10 Aanderaa standard.

The entire electronic circuit is mounted on a board inside the
Pressure Sensor and molded into Scotchcast. Other parts
exposed to water are made of titanium and this forms a compact and rugged sensor with no corrosion problems.

The sampling interval between measurements is controlled
by the data logging system and can be set in fixed steps
from 1 minute up to 3 hours.

The sensing element of these units, a small silicon chip with a
thin membrane at the centre, is subjected to atmospheric pressure on the one side and water pressure on the other. Four
diffused resistors on the chip, in the form of a Wheatstone
bridge, give an output signal proportional to the differential
pressure. The consequence of using monolithic technology

DATA SHEET D 325, SEPTEMBER 2000

The sensors tolerates operating submerged in purified
kerosene.

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