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The conductivity variation per each grade of temperature variation is a characteristic of the solution
and is indicated by the term "
temperature coefficient
α
T
": admissible values from 0.00 to
4.00%/°C,
default value 2.00%/°C
.
When a temperature sensor is present, the instrument automatically applies the temperature
compensation function, and proposes the measurement using the reference temperature according
to the coefficient
α
T
on the display.
Resistivity, TDS and salinity measurements
The HD 98569 instrument measures electric conductivity and temperature of a solution, and then
calculates resistivity, salinity and TDS. By repeatedly pressing “F3 = cond.” you can select the
measurement.
The resistivity is defined as the reciprocal of conductivity. The measurement is expressed in
Ω
cm
or one of the derived units (k
Ω
cm, M
Ω
cm or G
Ω
cm). It is generally used to measure pure and ultra
pure water.
The salinity is calculated using a more complex calculation: It is based on the assumption that the
measured conductivity is entirely and only due to the sodium chloride (NaCl) dissolved in the
water. It is expressed in g/l or mg/l.
The TDS (Total Dissolved Solids) is the measurement of the total concentration of ion species in
the solution. It is calculated by multiplying the conductivity measurement by a factor called “TDS
Coefficient”, set in the menu from 0.4 to 0.8 (MENU >> “Conductivity Options”
>>
“TDS
Coefficient”). The measurement of total dissolved solids is expressed in g/l or mg/l.
Calibration of conductivity
The probe calibration can be carried out on one to four points, using the standard solutions
automatically detected by the instrument (automatic calibration) or other solutions with known
temperature characteristics (manual calibration).
Technical note on the instrument functioning
The instrument uses four different automatically selected measurement scales: When the cell
constant is equal to 1, the four standard calibration solutions are associated to a different
measurement scale. The calibration solution at 147
μ
S/cm refers to the measurement scale 0, the
solution at 1413
μ
S/cm to the measurement scale 1, and so on. When the calibration point is
confirmed using the CAL key (see the details in the next paragraph), the display indicates the
calibrated scale (range) with the
;
symbol.
If the calibration was performed on multiple solutions, make sure that the
;
symbol is
displayed near a non yet calibrated range: It is useless to calibrate the same range twice
.
This warning is valid only if the cell constant is different from 1, and/or the solutions are not
standard.
Automatic calibration of conductivity using memorized standard solutions
The instrument can recognize four standard calibration solutions:
•
0.001 Molar KCl solution (147
μ
S/cm @25°C),
•
0.01 Molar KCl solution (1413
μ
S/cm @25°C),
•
0.1 Molar KCl solution (12880
μ
S/cm @25°C),
•
1 Molar KCl solution (111800
μ
S/cm @25°C),
By using one of these solutions, the calibration is automatic; the calibration can be carried out on
