Odyssey Xtreem - Principal of Operation; Installation Methods

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Odyssey

Xtreem

Capacitance Water Level Logger

User Manual

Principal of Operation

A capacitor consists of two conducting plates or cylinders separated by a non-conducting insulating

material. This insulator is called a dielectric. The value of the capacitor (if the distance between the

plates is fixed) is directly proportional to the area of the two plates in the capacitor.

The stability of the dielectric material governs the stability or quality of the capacitor. Teflon is used as

the dielectric in the Xtreem sensor sensors, as it is one of the best dielectric materials available and

also has good long-term stability. Teflon has zero moisture absorption; its characteristics are

therefore not altered by water immersion.

The Teflon-covered measuring element forms one plate of the capacitor and the Teflon is the

insulator or dielectric. The second plate is the water in which the sensor is immersed. As the water

level varies, the area of water that is in contact with the Teflon surface also varies. The water is like a

cylinder that is moving up and down the cylindrical Teflon-lined element. Hence the variation in

capacitance is directly proportional to the height variation of the water in contact with the Teflon. The

brass counterweight at the base of the sensor element is also used to make electrical contact with

the water.

The capacitance value is measured by the electronic module that is mounted at the top of the sensor

and recorded by the Odyssey

Xtreem logger that is also included in the electronic module. This

module converts the value of the capacitance into a digital signal so that the Odyssey

Xtreem logger

can measure the signal.

Installation Methods

The Xtreem water level sensor does not have a shroud on the sensor element. For open water

applications the sensor should be mounted inside a stilling well, this is best made with a PVC pipe.

Choose a location as far away from electrical noise sources as possible. If accurate ambient

temperature readings are required then the logger must be screened from direct sunlight. Attach a

sensor to the logger The connector is keyed so once this is lined up push the connector in as far as

goes and then rotate the top of the connector until it locks into place. The sensor should not come out

when light downward pressure is applied to the sensor connector. Do not pull on the sensor cable.

For groundwater measurement in water bores the sensor is simply lowered into the bore. The bore

casing or stilling well that the sensor is mounted in should be vertical, otherwise the Teflon element

may touch the side of the pipe that it is mounted in and water will be retained between the Teflon

element and the pipe. This will result in a measurement error at that point in the measurement range.

When the sensor is installed a manual water height measurement of the water level should be taken

so that a true starting point can be verified in the data when it is processed. This correction will take

into account any shift in the offset figure obtained when the sensor was calibrated. The manually read

water level measurement can be included in the calibration files relative level value. This will enable

actual true water levels to be calculated from a known datum point.

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