Measurement Parameters; Level; Pressure Calibration; Barometric Pressure - Solinst Levelogger Series User Manual

1.2 Measurement Parameters

1.2.1 Level

A = L - B
Figure 1-1
Levelogger Measurement Fundamentals

1.2.1.1 Pressure Calibration

The Levelogger 5 is calibrated against a range of set reference points to an accuracy of 3 decimal places.
During the calibration procedure, the Levelogger is fully submerged in a highly accurate water bath, until
conditions are stable. The pressure is then calibrated to six separate pressure points covering the entire range
of pressure to check for any non-linearity. The process is repeated again at two different temperatures to
check for temperature effects. Once done, the Levelogger is approved after all specifications for accuracy,
precision, stability and hysteresis have been met. The Levelogger should be calibrated for the life-time of the
instrument as long as it is used within its given technical specifications, in compatible monitoring environments
with routine inspections, and is not physically, chemically or thermally damaged.

1.2.2 Barometric Pressure

The Barologger 5 is designed for use in air only. It has a specific range and firmware algorithms based
on air pressure rather than water pressure. This makes the Barologger less accurate if used in water, but
more accurate if used as intended in air. Using a Barologger is the most accurate and convenient method
of obtaining atmospheric pressure and air temperature measurements, which are then synchronized to the
Levelogger. The Data Wizard in the Levelogger Software simplifies the adjustment of the level measurements
for barometric pressure changes, by generating a compensated data file using the synchronized data from all
Leveloggers on site and the site Barologger.
All Leveloggers measure total (absolute) pressure. When submerged,
the Levelogger is recording the combination of barometric pressure and
water pressure. The actual pressure of just water (
obtained by subtracting barometric pressure (
(see Figure 1-1).
The best method to compensate for barometric pressure is to employ
a Barologger above the water level, to obtain records of barometric
pressure. The Levelogger Software includes a Data Wizard, which guides
you through the automated process of barometric compensation. Manual
methods can be employed to determine the absolute water level using
barometric records collected on-site or available from a local weather station
(i.e. airport). Water level readings from Leveloggers are automatically
temperature-compensated.
A =
Actual water column height
B =
Barometric pressure
L =
Levelogger total pressure readings
D =
Depth to water level, below reference datum
Leveloggers measure the pressure of air plus water column above their
sensor (zero point). To adjust the level readings after data collection,
for example to water level depths below top of casing (D), refer to the
Advanced options within the software Data Wizard.
Note: The Levelogger Gold series convert pressure readings to the water level
equivalent above the datalogger's pressure zero point of 950 cm (31.17 ft). The
Levelogger 5 and Edge Series have no zero point offset. As such, water level
data will appear different, although measuring the same amount of pressure
(i.e. Levelogger 5 data will appear to be reading 950 cm (31.17 ft) higher
than a Levelogger Gold). Barometric Compensation using the Data Wizard,
automatically considers this zero point offset difference when compensating a
mix of models.
Levelogger Series User Guide
A
) above the sensor is
B
) from the total pressure (
L
)
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