5 | Measurement Basics
G 1410
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B-H87.0.01.DB200-2.0
5.4 Total dissolved solids / TDS measurement
The total dissolved solids measurement - TDS measurement - determines the total
dissolved solids, which also called evaporation residue, based on the conductivity and
a conversion factor CtdS of the total dissolved solids. Well-suited to conduct simple
concentration measurements of salt solutions. The display shows mg/l
Range
1
0 to 2000 mg/l
Display value TDS = conductivity [in µs/cm, nLF temperature compensation at 25°C] *
CtdS menu entry
With selection of TDS, the necessary temperature compensation is selected automat-
ically. Menu settings for temperature compensation are ignored.
The following approximations apply:
CtdS
0.50
Monovalent salts with 2 ion types = NaCl, KCl or similar
0.50
Natural water of surface water, drinking water
0.65 to 0.70
Salt concentration of aqueous fertiliser solutions
NOTE
These are guideline values for estimates, but are not suitable for precise measure-
ments. The conversion factor for the respective type of solution and the examined
concentration range must be determined for precise measurements. This can take
place with calibration to known comparison solutions or with actual evaporation of a
certain amount of liquid with measured conductivity and subsequent weight of the total
dissolved solids.
5.5 Salt content / salinity measurement
In
SAL
measuring mode, the salinity, which is the salt content of sea water, is determ-
ined. The basis for this is the International Oceanographic Tables, IOT. Standard salt
water has a salinity of 35 ‰, 35 g of salt per 1 kg of sea water. The display in % [g/kg]
normally does not show units. The designation PSU, Practical Salinity Unit, is also
commonly used; the display value is identical. The salinity measurement has temper-
ature compensation, which means the temperature is considered for the display and
has a major influence on the display value; any menu settings regarding temperature
compensation are ignored.
NOTE
The salt composition of different seas is not identical. Depending on the location,
weather, seasons, etc., there are considerable deviations from the 35 ‰ according to
the IOT. The salt composition can also influence the relationship of the salinity display
and the actual amount of salt present.
Corresponding tables are available for many salts in salt water aquarium applications.
Salt weight to salinity according to the IOT or conductivity. In consideration of these
tables, very precise salinity measurements can be conducted.
