Yokogawa EXA DC402 Dual-Channel Conductivity Analyzer - Manual (Page 36)

IM 12D08E02-01E
Parameter setting 5-11
5-2-5. Temperature compensation
1. Why temperature compensation?
The conductivity of a solution is very dependent on temperature. Typically for every 1 °C change in
temperature the solution conductivity will change by approximately 2 %.
The effect of temperature varies from one solution to another and is determined by several factors like
solution composition, concentration and temperature range.
A coefficient (a) is introduced to express the amount of temperature influence in % change in
conductivity/°C.
In almost all applications this temperature influence must be compensated before the conductivity read-
ing can be interpreted as an accurate measure of concentration or purity.
Table 5-1. NaCl-compensation according to IEC 60746-3 with T
ref
= 25 °C
T Kt a T Kt a T Kt a
0 0.54 1.8 60 1.76 2.2 130 3.34 2.2
10 0.72 1.9 70 1.99 2.2 140 3.56 2.2
20 0.90 2.0 80 2.22 2.2 150 3.79 2.2
25 1.0 --- 90 2.45 2.2 160 4.03 2.2
30 1.10 2.0 100 2.68 2.2 170 4.23 2.2
40 1.31 2.0 110 2.90 2.2 180 4.42 2.2
50 1.53 2.1 120 3.12 2.2 190 4.61 2.2
200 4.78 2.2
2. Standard temperature compensation
From the factory the EXA is calibrated with a general temperature compensation function based on a
sodium chloride salt solution. This is suitable for many applications and is compatible with the compen-
sation functions of typical laboratory or portable instruments.
A temperature compensation factor is derived from the following equation:
a = K t
- K
ref x 100
T - T
ref
K
ref
In which:
a = Temperature compensation factor
(in %/ °C)
T = Measured temperature (°C)
K
t
= Conductivity at T
T
ref
= Reference temperature (°C)
K
ref
= Conductivity at T
ref
3. Manual temperature compensation
If the standard compensation function is found to be inaccurate for the sample to be measured, the con-
verter can be set manually for a linear factor on site to match the application.
The procedure is as follows:
1. Take a representative sample of the process liquid to be measured.
2. Heat or cool this sample to the reference temperature of the converter (usually 25 °C).
3. Measure the conductivity of the sample with the EXA and note the value.
4. Bring the sample to the typical process temperature (to be measured with the EXA).
5. Adjust the display indication to the noted value at the reference temperature
6. Check that the temperature compensation factor has been changed
7. Insert the conductivity cell into the process again.
4. Other possibilities (section 5-3-3)
1. Enter calculated coefficient.
2. Enter matrix temperature compensation.