In-Situ Aqua TROLL 100 and 200 Operators Manual - Manual (Page 48)

Page 48 Aqua TROLL Operator’s Manual
Section 5: Conductivity
enable the comparison of data from experiments with different
conductance cells, the conductance is multiplied by the cell
constant to show conductivity in Siemens per centimeter (S/cm).
Cell constants are determined for each sensor using a standard
solution of known conductivity. The cell constant depends on
the electrode area and the amount of separation or distance
between the electrodes.
The four-electrode conductivity cell contains two drive
electrodes and two sensing electrodes. In the Aqua TROLL
instrument, each drive electrode is composed of two
interconnected pins, for a total of six pins. The sensing electrodes
are positioned in a low current area to minimize electrode
fouling. An alternating current is used to drive the cell. This
reduces errors caused by polarization resulting from the
application of a direct current.
Calibration
The conductivity sensor in the Aqua TROLL instrument has been
calibrated during manufacturing to produce a linear response
across the operating range. Standard Operating Procedures
for measuring conductivity in the field typically specify that
the sensor shall be calibrated before use, close to the expected
temperature and conductivity conditions. The accuracy of
the sensor depends on the calibration solution used and the
operator’s technique.
We recommend that you check the specific conductivity reading
in the solution shipped with your instrument. If the device
is reading accurately, there is no need to field-calibrate the
instrument unless SOPs require it.
The Aqua TROLL instrument can be calibrated at any point in the
operating range. However, best results will be obtained in the
TIP: When
calibrating below
1,000 µS/cm,
additional care must be taken
to prevent the calibration
solution from drifting due to
atmospheric exposure.