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<5. CALIBRATION>
5-1
IM 12F5A2-01E
5. CALIBRATION
Perform zero and span calibration when the analyzer is to be initially started up and also when
re-operated after prolonged shutdown.
During operation, perform span calibration periodically (approx. once a month). When span is to
be calibrated, first polish the indicator electrode (see subsection 6.1.1) and then perform running-
in operation for approx. one hour.
Zero calibration is virtually unnecessary during operation if it is performed once at start-up. How-
ever, merely confirm periodically that the zero point is correct during operation.
5.1
Zero Calibration
There are two methods for calibrating zero: the “open input circuit method” using which the
calibration is performed by pulling up the rotating and counter electrodes from the sample water
and the “chlorine-free water method” using water free from chlorine (e.g., water filtered through
activated carbon). Normally calibrate zero using the “open input circuit method”. However, if free
available chlorine of low concentration is always to be measured (e.g., approx. 0.1 mg/l), use the
“chlorine-free water method” for zero calibration.
5.1.1
Zero Calibration Procedure Using the Open Input
Circuit Method
(1) Remove the electrode assembly from the measuring tank with the indicator electrode ro-
tated and fix it to the holding studs. (Remove the electrode assembly by loosening the two
fixing screws.)
It is not necessary to stop the sample water.
(2) After display of the free available chlorine concentration has stabilized, perform zero calibra-
tion. First, remove the terminal cover.
Next, slowly turn the zero calibrator (potentiometer) using the attached flat blade screwdriv-
er to adjust display to zero.
(3) Mount the terminal cover. Return the electrode assembly to the measuring tank and tightly
fix the assembly using the two fixing screws.
5.1.2
Zero Calibration Procedure Using Chlorine-Free Water
Method
(1) Prepare two to three litre of chlorine-free water (prepared by adding 10 ml/l of pH 7 buffer
solution and 50 mg/l of NaCl to purified water).
(2) 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.
(3) Introduce the chlorine-free water into the measuring tank.
Connect a tube to the sample water inlet and pour the chlorine-free water 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.
(4) After the free available chlorine concentration display has stabilized, perform zero calibra-
tion. First, remove the terminal cover.
Next, slowly turn the zero calibrator (potentiometer) using an attached flat blade screwdriver
to adjust display to zero.
(5) Mount the terminal cover. Also stop supply of the chlorine-free water.
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.
Содержание FC500G
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