In-Situ TROLL 9500 Operators Manual - Manual (Page 83)

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TROLL 9500 Operator’s Manual 0095110 rev. 007 01/09
USING A CONDUCTIVITY METER AS A SECONDARY STANDARD
If a conductivity meter is available for comparison, the cell constant
(Kcell) for the conductivity sensor can be calculated by hand and
entered manually into the software.
1. Note the current cell constant. Immerse the MP TROLL with con-
ductivity sensor in a solution. Take and record the reading.
2. Take and record a reading in the same solution with a conductivity
meter.
3. Solve the following for X:
4. This is the new cell constant. Enter this value in the software as
described below.
ENTERING A CELL CONSTANT MANUALLY
A cell constant may be entered “manually” without running a complete
calibration.
1. With a conductivity sensor installed, establish a connection to the
instrument in Win-Situ 4 or Pocket-Situ 4.
2. Select Conductivity in the Parameters list and click Calibrate.
3. Select Other, and key in any reasonable value. Press Next twice to
get to the final screen.
4. In the final screen, key in the desired cell constant.
5. Click Finish to send the new value to the sensor.
UNITS AND CALCULATED MEASUREMENTS
Basic Unit: AC
Absolute (or “actual”) conductivity, without temperature compensation,
is the basic unit for the conductivity sensor. Measurements may be
displayed in:
microSiemens per centimeter (μS/cm AC)
milliSiemens per centimeter (mS/cm AC)
The following units are also available for displaying derived measure-
ments calculated from the conductivity channel output:
TIP: To change unit preferences: In Win-Situ, select
Preferences on the Options menu. In Pocket-Situ, select the
Home site, then tap Setup in the command bar.
TIP: Since the specific ionic composition of all analytes
cannot be known, the conversions provided in the software
are reasonably good estimates of Specific Conductance and
Total Dissolved Solids. The resulting derived values should be
treated with caution.
Specific Conductance (SC)
3PECIlC
The conversion requires a temperature coefficient for the solution
being measured. By convention, the temperature coefficient for potas-
sium chloride (KCl) calibration standards is used. Specific conduc-
tance is calculated from:
where
AC is the actual conductivity in μS/cm
0.0191 is a nominal temperature coefficient for KCl solutions
Temp. is the solution temperature in degrees C.
The correction factor of 0.0191 (1.91% / ½#
reasonable approximation for samples containing sodium and chloride
salts (i.e., seawater). For comparison, the table below lists correction
factors for other solution types.
Solution Correction factor
(%/ o C)
5% H
2
SO
4
0.96
10% HCl 1.32
5% NaOH 1.7
Dilute NH
3
1.88
KCl salt (default) 1.91
NaCl salt 2.12
98% H
2
SO
4
2.84
Ultrapure water 4.55
Sugar solution 5.64
Units: microSiemens per centimeter (μS/cm SC)
Current Kcell
Reading with this Kcell
X
Conductivity meter reading
=
AC
[1 + 0.0191 (Temp. – 25.0)]
SC =
SECTION 12: CONDUCTIVITY