44
SECTION 4,
continued
3. When the conductivity value stabilizes, store or record it.
Note: If the non-temperature-corrected conductivity of the sample
increases above 1 µS/cm, the meter will use the temperature
correction coefficients for NaCl. This may cause a noticeable jump in
the displayed conductivity reading.
4.5
Measuring Total Dissolved Solids
To measure TDS with the sens
ion
156 meter, press the
CON/TDS/SAL
key until the TDS icon appears in the lower left
corner of the screen. The instrument will display the TDS value
for the currently displayed conductivity measurement.
The standard method of determining TDS is to evaporate the
sample to dryness at 180 °C, then weigh the residue.
Alternatively, calculate the concentration of sodium chloride that
would have the same conductivity as the sample at the same
temperature. The sens
ion
156 meter reports a sample’s TDS
value in mg/L of sodium chloride by comparing the sample
conductivity and temperature to data stored in the meter’s
memory. Data were obtained from empirical procedures using
sodium chloride solutions.
4.6
Measuring Salinity
To measure salinity with the sens
ion
156 meter, press the
CON/TDS/SAL
key until the SAL icon appears in the lower left
corner of the screen. The instrument will display the salinity
value for the sample being measured.
Salinity, a measure of the mass of dissolved salts in a given mass
of solution, is used to describe seawater, natural, and industrial
waters. Salinity is a relative scale based on a potassium chloride
(KCl) solution. A salinity value of 35 is equivalent to a KCl
solution containing 32.4356 g KCl in 1 kg of solution at 15 °C.
Salinity is measured in ‰ (ppt—parts per thousand). The meter
calculates the salinity based on the Extended Practical Salinity
Scale of 1978, as referenced in 17
th
edition of Standard Methods,
25200 B. The applicable range is 0 to 42‰ and –2 to 35 °C.
If you have a DO probe and plan to use salinity measurements to
adjust DO measurements, follow the steps below:
