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<5. CALIBRATION>
5-2
IM 12F5A2-01E
5.2 Span Calibration
There are two span Calibration methods: “sampling method’’ using which calibration is performed
based on the manually analyzed free available chlorine concentration of sample water, and the
“standard solution method” which allows calibration using a standard calibration solution having a
free available chlorine concentration of approximately 80 % of the measuring range.
Calibrate the analyzer span using the “sampling method’’ unless the chlorine concentration of
sample water is near zero. (Span calibration can be performed without removing the terminal
cover).
Note: Before performing span calibration, confirm that the electrode does not remain exposed to
the air as after zero calibration, and the electrode rotates normally in the measuring tank.
5.2.1 Span Calibration Procedure Using the Sampling
Method
(1) Confirm that the free available chlorine concentration in the sample water is stable by ob-
serving displayed values.
(2) Sample the sample water by loosening the drain cock at the bottom of the measuring tank.
When sampling the sample water, exercise care so that the tip of the counter electrode is
not exposed to air above the level of the sample water.
(3) Quickly measure the free available chlorine concentration of the sampled sample water, us-
ing a manual analysis such as amperometric titration (AT method).
(4) Slowly turn the span calibrator (potentiometer) using the attached flat blade screwdriver to
adjust display to the manually analyzed value.
5.2.2 Span Calibration Procedure Using Standard Solution
Method
(1) Prepare diluting solution which is obtained by adding 10 ml/l of pH 7 buffer solution and 50
mg/l of NaCl to purified water (sample water can also be used instead of purified water).
(2) Prepare 2 to 3 liter of the standard solution conditioned to a free available chlorine concen-
tration of approximately 80 % of the measuring range. To obtain this solution, dilute commer-
cially available sodium hypochlorite (NaClO) solution using the diluting solution prepared in
step (1).
(3) Stop supply of sample water and wait until the sample water level in the measuring tank
decreases to below the sample water inlet. Then disengage the sample water inlet piping.
(4) Introduce the standard solution into the measuring tank.
Connect a tube to the sample water inlet and pour the solution contained in a suitable vessel
into the measuring tank by utilizing a head from the inlet. If a pump is used for supply, use a
flow rate of 100 ml/min or more.
(5) After the free available chlorine concentration display has stabilized, loosen the drain cock
to sample the standard solution.
In sampling the solution, exercise care so that the tip of the counter electrode is not exposed
to air above the level of the solution.
(6) Quickly measure the free available chlorine concentration of the sampled sample water, us-
ing a manual analysis such as amperometric titration (AT method).
(7) Slowly turn the span calibrator (potentiometer) using the attached flat blade screwdriver to
adjust display to the manually analyzed value.
(8) Stop supply of the standard solution.
After the solution level in the measuring tank decreases to below the sample water inlet,
remove the tube and restore the sample water piping connection.
Supply sample water.