YOKOGAWA FC400G, User Manual, Page: 62 / 91

< 7. Calibration >
7-1
IM 12F5A1-01E
7. CALIBRATION
Calibration is required to correctly measure free chlorine concentrations using the FC400G.
Calibration is performed for the zero point and span. There are two methods to calibrate the zero
point: open input circuit and chlorine-free-water-based measurement methods. Also, there are two
span calibration methods: sampling and standard solution methods. Calibration is performed at start-
up or when operation is restarted after being stopped for a long period of time.
Also, calibration is performed periodically (recommended every month or so) during operation. This
chapter describes the calibration procedure.
7.1 Running-in
In general, calibration requires running-in. Always run in the FC400G at start-up or when it restarts
after being temporarily stopped.
Running-in requires, first, polishing of the indicator electrode. Comply with Sec. 6.1.4 on how to polish
the indicator electrode.
After polishing, install the polished indicator electrode and select “CELL. ON” in the <CELL> mode.
Then press the
YES
key to rotate the electrode. Operate the free available chlorine analyzer for
approx. one hour.
Calibration can be conducted after this approx. 1 hr running-in.
Note: It is recommended that electrode polishing be performed even when calibration is performed periodically during operation.
However, electrode polishing can be omitted if the calibration interval is short and it can be determined that the electrode is not
contaminated.
The characteristic readings of the indicator electrode are temporarily not stable immediately after polishing the electrode.
Therefore, after electrode polishing is performed, leave the FC400G running for a while (approx. 1 hour) under the measurement
conditions until the characteristic readings of the indicator electrode stabilize. Calibration is performed following this running-in.
7.2 Zero Calibration
The method of calibrating the zero point of the free available chlorine analyzer includes two
approaches; open input circuit and chlorine-free-water-based measurement methods.
In the former the electrode is exposed in the air so that no current flows between the indicator
electrode (rotating electrode) and counter electrode. The latter uses chlorine-free water (e.g., water
filtered through activated charcoal).
During auto zero calibration with the activated charcoal filter, chlorine-free (chlorine not included)
water must be used.
If the FC400G generally measures free chlorine concentrations as low as 0.1 mg/l, conduct zero
calibration using the chlorine-free-water-based measuring method.
However, the open input circuit method, easy to conduct, is generally used.