6 Reference
113
6.6
Salinity (SAL) conversion
The U-50 series is designed to calculate salinity as well as the other parameters.
Note that the “salinity” here is the salinity of sea water. There is a constant relation between
conductivity and salinity at certain temperatures.
Therefore, if data on the conductivity and temperature are available, the corresponding salinity
can be known. In other words, the salinity measurement of the U-50 series is based on the
principle of calculating the salt content, making use of the measured values of conductivity
and temperature.
Note therefore, that measured results of all substances whose conductivity is detected are
displayed as salinity. For example, the measured result is displayed as NaCl concentration,
even if in fact the sample component is, hydrochloric acid (HCl).
6.7
TDS conversion
TDS is short for Total Dissolved Solids and means the total dissolved solid amount.
The conductivity of a solution is affected by the amount of salinity, minerals, and dissolved
gases. That is, conductivity is an index that shows the total amount of all substances in the
solution. Of these substances, TDS indicates only the amount of dissolved solids.
TDS can be used for a comparison of the state of substances composed of a single
component such as NaCl. However, the use of TDS for the comparison of solutions of different
types causes serious errors.
Conductivity and TDS are expressed by the following formulas.
Conductivity in SI units (S/m) ....................... TDS(g/L) = L (S/m)
K
10
TDS(g/L) = L (mS/m)
K
100
Conductivity in the old units (mS/cm) .......... TDS(g/L) = L (mS/cm)
K
K = TDS coefficient
Initial settings use the values listed in the table (Page 80) that generally uses TDS coefficients.
For accurate TDS comparisons, find the TDS coefficient from measured conductivity values.
Then set the value thus obtained and make measurements.
6.8
t
conversion
Specific gravity of seawater
The density and specific gravity of seawater are equal numerically and generally are not
distinguished strictly. Since seawater density
is between 1.000 and 1.031, 1 is subtracted
from
and
is obtained by multiplying the value by 1000.
The resultant value is used as the specific gravity of seawater.
= (
- 1)
1000
The density of seawater
is expressed by function of temperature, hydraulic pressure, and
salinity. The density of seawater under the atmospheric pressure is expressed as
t
. The
density of seawater under the atmospheric pressure is determined by temperature and
salinity.
The U-50 Series models make salinity measurement through temperature measurements and
conductivity conversion and find
t
through calculations.
In Japan
15
at 15°C is called a standard specific gravity and widely used while in foreign
countries
0
at 0°C is employed.
15
and
0
are determined by the function of salinity.
In ocean surveys, in particular, these values
t
,
15
, and
0
are more widely used than
conductivity and salinity and, in the U-50 Series models, newly added as measurement
components.
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