YOKOGAWA FC400G, Руководство пользователя, Страница: 12 / 91

< 1. Overview >
1-3
IM 12F5A1-01E
1.2 Measuring Principle of FC400G Free Available
Chlorine Analyzer
The FC400G free available chlorine analyzer applies the polarographic method using a rotating
electrode, as the measuring principle to measure free available chlorine existing in the form of chlorine
(Cl
2
), hypochlorous acid (HClO), and hypochlorite ions (ClO
-).
The FC400G applies external voltage between the indicator electrode (rotating electrode) and
counter electrode (silver chloride electrode) to electrolytically reduce free available chlorine, and then
measures the diffusion current flow during the above voltage application to obtain the concentration
of free available chlorine. The voltage to be applied is selected from among values in the area where
current value remains stable even if the voltage value changes, i.e., the area (plateau area) where
concentration polarization occurs in polarography. Since this applied voltage changes according
to the diffusion current value, the FC400G free available chlorine analyzer performs compensation
complying with this change, to apply suitable voltage. Further, this obtained diffusion current value
also changes with temperature, and the current is automatically corrected using signals from the RTD
(Pt 1000 Ω) built in the counter electrode.
The FC400G free available chlorine analyzer was designed to require minimal maintenance and uses
no reagent. However, it must be understood that there are restrictions on the conditions of the water to
be measured (sample) in comparison with the RC400G Residual Chlorine Analyzer that uses reagent.
Also, note that if combined chlorine is present in sample, FC400G performance is affected.
Figure 1.2 shows the measuring circuit principle of the FC400G free available chlorine analyzer. The
FC400G applies voltage compensated in accordance with the diffusion current value, between the
indicator and counter electrodes and measures the diffusion current flow between the electrodes.
Temperature compensation is accomplished using the CPU which performs calculation based on the
temperature signals received from the temperature-measuring circuit.
F1.2e.ai
Is
ME
Amplifier
Current/
voltage
conversion
circuit
Voltage
apply-
ing
circuit
Tempe-
rature-
measur-
ing
circuit
RE (Applied-voltage
compensation)
Measuring tank
Indicator Electrode Counter Electrode
CPU
LCD
Current/
voltage
output
circuit
4 to 20 mA or
1 to 5 V
Figure 1.2 Measuring Circuit Principle