17
“COMPENSATION”
Conductivity measurements are temperature dependent. The degree to which temperature affects conductivity varies
from solution to solution and can be calculated using the following formula:
Gt = Gtcal {1 + a(T-Tcal)}
where: Gt = conductivity at any temperature T in °C, Gtcal = conductivity at calibration temperature Tcal in °C,
a = temperature coefficient of solution at Tcal in °C.
Substance at 25°C
Concentration
Alpha (a)
HCl
10
wt%
1.56
KCl
10
wt%
1.88
H
2
SO
4
50
wt%
1.93
NaCl
10
wt%
2.14
Common alphas (a) are listed in the table above. To determine that (a) of other solutions, simply measure conductivity
at a range of temperatures and graph the change in conductivity versus the change in temperature. Divide the slope
of the graph by Gtcal to get a. Temperature compensation (Alpha) can be changed within 0.0% and 5.0%. It should
be set according to measured chemical properties.
If a temperature probe is installed choose “Enable” for “Automatic”. Otherwise select “Disable” and enter a
temperature value in “Temperature” field. If the controller is connected to a temperature probe, check the
“Automatic” field: temperature compensation is automatic. Otherwise choose to leave the field blank and enter a
value of average temperature in the system under which compensation must be made (field TEMPERATURE).
Options are:
ENABLE
(tick to enable on the basis of the following parameters for the
temperature compensation)
ALPHA
(see explanation above)
AUTOMATIC
(tick to enable automatic temperature compensation based
on the reading provided by the PT100 sensor installed)
TEMPERATURE
(manually enter a fixed value, if there is any installed
temperature probe)
Note: when “AUTOMATIC” is enabled the “TEMPERATURE” field is not available.
