24
Operation
Figure 27 Setup pH
Setup pH
→ Setup → pH
Select USA auto-buffer recognition (4.01, 7.00, and 10.00) or NIST auto-
buffer recognition (4.01, 6.86, and 9.18) (Figure 27).
Figure 28 Setup Conductivity
Setup Conductivity
→ Setup → Conductivity
Temp Ref (Temperature reference): Reference temperature used to
calculate temperature compensated specific conductance. All specific
conductance values are compensated to the Temp Ref temperature. The
default value is 25 °C (77 °C) (Figure 28). Enter a new value between
15.00 °C (59 °F) and 25.00 °C (77 °F).
%/°C (Percent per degree Celsius): Temperature coefficient used to
calculate temperature compensated specific conductance. The default is
1.91% based on KCl standards. Enter a new value between 0 and 4%.
TDS Constant: Multiplier used to calculate an estimated Total Dissolved
Solids (TDS) value from conductivity. The multiplier is used to convert
specific conductance in mS/cm to TDS in g/L. The default value is 0.65.
Enter a new value between 0 and 0.99.
This multiplier is highly dependent on the nature of the ionic species
present in the water sample. To be assured of moderate accuracy for
the conversion, you must determine a multiplier for the water at your
sampling site. Use the following procedure to determine the multiplier
for a specific sample:
1. Determine the specific conductance of a water sample from the
site.
2. Filter a portion of water from the site.
3. Carefully measure a volume of the filtered water. Completely
evaporate to yield a dry solid.
4. Accurately weight the remaining solid.
5. Divide the weight of the solid (in grams) by the volume of water
used (in liters) to yield the TDS value in g/L for the site.
6. Divide the TDS value in g/L by the specific conductance of the
water in mS/cm to yield the conversion multiplier.
NOTE: Make sure to use the correct units.
NOTE: If the nature of the ionic species at the site changes
between sampling studies, the TDS values will be in
error. TDS cannot be calculated accurately from specific
conductance unless the make-up of the chemical species in
the water remains constant.
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