YSI 3100 - Manual (Page 30)

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The cell you use for small sample applications depends upon the
quantity of solution available and the conductivity of the
solution. The 3401 cell (K=1.0/cm) requires 15 mL, the 3256
and 3402 cells (K=0.1/cm) require 12 mL, the 3253 and 3403
cells (K=1.0/cm) require 3 mL, and the 3252 and 3417 cells
(K=1.0/cm) require 1 mL of sample.
When a dip cell is used as a fill cell, the cell's vent hole is sealed
and the electrode chamber is inverted and filled with solution,
changing the cell constant (K). The cell will require calibration
after being configured as a fill cell.
Conductivity System Accuracy Considerations
System accuracy for conductivity measurements is equal to the sum of the errors contributed by
the environment and the various components of the measurement setup. These include:
•
Instrument accuracy
•
Cell-constant accuracy
•
Temperature measurement accuracy
Instrument Accuracy
YSI meters are very accurate; however, each instrument and range has its own accuracy
statement and therefore, must be accounted for in the overall accuracy determination.
Cell-Constant Accuracy
YSI cells are warranted to be accurate to within one percent, for more accurate work you should
calibrate the cell to determine the exact cell constant.
Temperature Accuracy
The solution temperature accuracy is the sum of the instrument accuracy plus the temperature
sensor accuracy.
If the conductivity is to be expressed at 25
°
C, some additional errors will be introduced either by
the instrument's temperature correction electronics or by the mathematics used for the conversion
to 25
°
C.
7.3 Salinity
Salinity is determined automatically from the Model 3100 conductivity and temperature readings
according to algorithms found in Standard Methods for the Examination of Water and
Wastewater (ed. 1995). The use of the Practical Salinity Scale 1978 results in values which are
unitless, since the measurements are carried out in reference to the conductivity of standard
seawater at 15°C. However, the unitless salinity values are very close to those determined by the
previously-used method where the mass of dissolved salts in a given mass of water (parts per
thousand) was reported. Hence, the designation "ppt" is reported by the instrument to provide a
more conventional output.