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6. GENERAL CALIBRATION & MAINTENANCE PROCEDURE
6.1 Calibration of the sensor
The conductivity sensors are factory
calibrated traceable to NIST standards.
The cell constant values are indicated on
the sensor or on the integral cable of the
sensor. The cell constant value can be
entered directly in the Yokogawa
analyzer. The procedure is explained in
the Instruction Manual of the analyzer
the sensor has been subject to abrasion
(erosion or coating) in the process, re-
calibration of the sensor may be
necessary. Refer to the Instruction Manual
of the analyzer for a detailed description.
Note 11 : During calibration the
temperature compensation is still active.
This means that the display reading refers
to the default reference temperature
(25 °C). Calculations for calibrations (CC,
TC, or temp) make use of the
uncompensated raw measurement data.
Calibration is normally carried out by
measuring a solution with a known
conductivity value at a known
temperature. These solutions are
commercially available. You can make
your own solution by dissolving an
amount of salt in water. Table 9 and 10
show some typical conductivity values for
Sodium Chloride (NaCl) and Potassium
Chloride (KCl) solutions which can be
made, preferably in a laboratory. The
tables are derived from the standards laid
down in 'International Recommendation
No. 56 of the Organisation Internationale
de Métrologie Legale'.
6.2 Periodic maintenance of the sensor
In general conductivity sensors do not
need much periodic maintenance. In case
the sensor has become fouled, an
insulating layer may be formed on the
surface of the electrodes, and
consequently giving a measuring error.
Cleaning the sensor will solve this
problem. Effective cleaning methods are
given below
1. Normal applications: hot water with
some commercially available washing-up
liquid.
2. Lime, hydroxides or similar
applications: 5 % solution of hydrochloride
acid.
3. Organic (e.g. oils, fats) applications:
11
. If
alcohol or iso-propanol.
4. Algae, bacteria or fungus: solution of
commercially available bleach
(hypochlorite).
Note 12 : Read the instructions on the
package of the cleaning agents for safe
use.
Table 9: Conductivity values of KCl at
25 °C (OIML)
Weight
%
0.3
0.5
1
3
5
10
Table 10: NaCl values @ 25 °C
(IEC 746-1)
Weight %
0.001
0.003
0.005
0.01
0.03
0.05
0.1
0.3
0.5
1
3
5
10
11
:
Molal
mg of KCl /
(m)
kg of sol.
0.001
74.66
0.002
149.32
0.005
373.29
0.01
745.263
0.1
7419.13
1.0
71135.2
mg/kg
Conductivity
10
21.4 µS/cm
30
64.0 µS/cm
50
106 µS/cm
100
210 µS/cm
300
617 µS/cm
500
1.03 mS/cm
1000
1.99 mS/cm
3000
5.69 mS/cm
5000
9.48 mS/cm
10000
17.6 mS/cm
30000
48.6 mS/cm
50000
81.0 mS/cm
100000
140 mS/cm
IM 12D07J03-01EN-P
29
Conduct.
in mS/cm
0.1469
0.2916
0.7182
1.4083
12.852
111.31
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