YOKOGAWA RC400G, User Manual

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<7. Calibration>
7-1
IM 12F4A1-01E
7. Calibration
Calibration should be implemented at startup or when analyzer operation is restarted after
prolonged operation suspension, and also periodically during operation (nearly once a
month).
This chapter describes “running-in” operation conducted when calibration is to be
executed and the calibration procedure.
7.1 Running-in Operation
Conduct “running-in” operation in principle when calibration is to be implemented. Conduct
“running-in” operation without fail when calibration is to be performed at analyzer startup or after
prolonged analyzer operation suspension, or for calibration when values displayed with function
code “8” or “9” in <MEAS.> mode greatly deviate from the reference values.
When the temperature falls below zero degrees Celsius, “running-in” operation for about 1 hour is
recommended.
Start “running-in” operation at polishing of the indicator electrode. For the polishing procedure,
conform to subsection 4.3.10.
After mounting the polished indicator electrode, press [CELL] key and rotate the electrode. Leave
the analyzer to operate in <MAINT.> mode.
Calibration should be performed after continuing this “running-in” operation for about 30 min.
When new sand is used in the sand filters of the RC400G-2 or RC400G-3 residual chlorine
analyzer, chlorine in the sample water may be absorbed by the sand, resulting in measurement
errors. Upon startup or after sand is replaced, allow water to run for 2 to 3 hours, and perform
calibration after the reading has stabilized. Furthermore, allow water to run for about one day for
complete stabilization of sand, and then perform calibration again.
7.2 Zero Calibration
Calibration methods for residual chlorine analyzer zero point include the “open input circuit
method” and “chlorine-free water method”.
The “open input circuit method” is a calibration method which is conducted with no current
flowing between the indicator electrode (rotating gold alloy electrode) and the counter electrode
exposing the electrodes in the air. The “chlorine-free water method” is a calibration method which
is conducted using water that does not contain chlorine.
In general, perform zero calibration using the simple open input circuit method. However, when
trace residual chlorine (0.1 ppm) is to be usually measured, conduct the zero calibration using the
chlorine-free water method.
7.2.1 Zero Calibration Using Open Input Circuit Method
Perform zero calibration using the open input circuit method in the following procedure:
(1) Press [CELL] key in <MAINT.> mode to stop turning of the indicator electrode. When the
electrode rotation is in stopping status, <CELL> lamp extinguishes.
Next, the electrode mechanism block is removed from the measuring tank (see Figure 4.7).
(2) Set the function code to “1”. The content of this code is “zero calibration”.
(3) Start calibrating operation. Press [ENT] key.
During calibrating operation, <CAL> lamp flashes. Calibration is performed when the
analyzer stabilizes so that predetermined conditions (see subsection 5.3.4 (4)) are met after
measured value stability is automatically checked.
When calibration is executed, the value displayed in the data display flashes once and, at
the same time, flashing <CAL> lamp extinguishes.
14th Edition : Jul. 15, 2020