IM 12D08N04-01E
5-12
5. Parameter Setting
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 (
α
) 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 reading can be interpreted as an accurate measure of concentration or
purity.
Table 5-1. NaCl-compensation according to IEC 746-3 with T
ref
= 25
°
C
T
a
T
a
T
a
T
a
T
a
0
1.8
50
2.1
90
2.2
140
2.2
190
2.2
10
1.9
60
2.2
100
2.2
150
2.2
200
2.2
20
2.0
70
2.2
110
2.2
160
2.2
30
2.0
80
2.2
120
2.2
170
2.2
40
2.0
90
2.2
130
2.2
180
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 compensation functions of typical laboratory or portable
instruments.
A temperature compensation factor is derived from the following equation:
Kt-K
ref
T-T
ref
x
100%
K
ref
a
=
a
= Temperature compensation factor (in % /
8
C)
T = Measured temperature (
8
C)
Kt = Conductivity at T
Tref = Reference temperature (
8
C)
Kref = Conductivity at Tref
T5.2.3A.eps
3. Manual temperature compensation
If the standard compensation function is found to be inaccurate for the sample to be
measured, the converter 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. Press the MODE key to enter the calibration mode (see section 6-2).
Содержание SC402G
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Страница 25: ...IM 12D08N04 01E 3 12 3 Installation and Wiring...
Страница 63: ...IM 12D08N04 01E 6 4 6 Calibration...
Страница 69: ...IM 12D08N04 01E 9 2 9 Spare Parts...
