Yokogawa 2-Wire Dual Channel Transmitter/Analyzer FLXA21 - Manual (Page 225)

App.2-9
IM 12A01A02-01E 5th Edition : Oct. 31, 2013-00
n Temperature compensation error
The temperature compensation error (alarm) is issued in any of the following cases.
l TC
The error is issued when:
(measured temperature – reference temperature) < –90/compensation coefficient
The default of the temperature compensation coefficient is 2.10%/°C.
For example, when the reference temperature is 25°C, the temperature compensation coefficient
is 2.10%/°C and the measured temperature is lower than –17.9°C, the error will be issued.
Temperature compensation is performed even while an alarm is being issued.
l Matrix
The error is issued when the temperature or the precompensated conductivity is out of the range
of the temperature compensation matrix.
In this case, however, the temperature compensation is performed by extrapolation even while
an alarm is being issued.
l All
When the conductivity is around zero, the temperature compensation error may be issued. In this
case, the temperature compensation is not performed, and the precompensated conductivity is
displayed.
Whether the conductivity is around zero or not is determined by the temperature and conductivity
of solutions. For example, when the temperature is 20°C and the conductivity is lower than 0.033
μS/cm, the conductivity is determined to be around zero.
When measuring the conductivity around zero in air calibration or when the conductivity to be
measured is around zero, an alarm may be issued.
NOTE
To display the precompensated conductivity, set the Method to “None”.
Select Measurement setup → Temp. compensation.
n TDS readings
The concept of Total Dissolved Solids (TDS) is widely used as an indication of the total solute
concentration in water and is a widely accepted water quality standard. The determination is
simply made by evaporation and weighing the residue. As the heat treatment converts the
chemical properties of the solution, some solutes that contribute to the total conductivity will not
be found in the residue. Also some combinations of solutes will become volatile at the drying
temperature. The same applies for those solutes that do not contribute to the conductivity but do
end up in the residue. When one (or a few) solute is dominant in the solution, these problems
may be neglected and TDS will have a direct correlation with the conductivity.
Next is a graph that shows the correlation between the specific conductance and concentrations
(by weight) for six salts. The factor by which the conductivity should be multiplied to come to
a TDS reading ranges from 0.4 to 0.7 up to a conductivity of 500 µS/cm. At a conductance of
approximately 3000 µS/cm the range would be from 0.5 and 1.0.
The FLXA21 measures conductivity. This value can be used to display TDS values on the main
display. One should use the additional concentration table. The unit for the TDS reading can be
set to ppm or ppb.
App.
SC