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For practical reasons, the salinity of a solution is derived from the salinity of the seawater. Two methods
of calculating the salinity from the conductivity are supported:
• Natural seawater scale
• Practical salinity scale
Natural seawater scale (UNESCO 1966)
According to the definition, salinity of a sample in ppt is calculated using the following formula:
r
T
=1.0031·10
‑9
T
4
–6.9698·10
‑7
T
3
+1.104259·10
‑4
T
2
+2.00564·10
‑2
T+6.766097·10
‑1
R=R
T
+10
‑5
R
T
(R
T
–1.0)(T–15.0)[96.7‑72.0R
T
+37.3R
T
2
–(0.63+0.21R
T
2
)(T–15.0)]
S=‑0.08996+28.212.80832R
2
–10.67869R
3
+5.98624R
4
–1.32311R
5
where:
R
T
‑ coefficient;
C
T
(sample) ‑ uncompensated conductivity at T °C;
C(35;15)= 42.914
mS/cm ‑ the corresponding conductivity of KCl solution
containing a mass of 32.4356 g KCl / 1 Kg solution;
r
T
‑ temperature compensation polynom.
Note: The formula can be applied for temperatures between 10
°
C and 31
°
C.
To access this range press Mode while in Salinity range until the seawater scale [SW] is
displayed.
Practical salinity scale
This is a practical scale based on the precise measurement of the electrical conductivity of a solution
with a known salinity range.
The relationship derived from the scale relates salinity, conductivity, temperature and pressure
and use a solution with a salinity of 35 ‰ as datum point. This is taken to have a conductivity
of 42.914 mS/cm of 15 °C at standard atmospheric pressure.
R
T
=
C
T
(sample)
C(35;15)·r
T
OPERA
TIONAL GUIDE