YOKOGAWA RC400G, User Manual

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<1. Outline>
1-4
IM 12F4A1-01E
Therefore, the voltage to be applied is selected as a value at which the so-called polarograph
concentration polarization occurs, that is, current does not change when voltage changes. For
measuring total residual chlorine, -0.40 V is applied.
The diffusion current observed under this condition is approx. 2.0 µA/mg/l in reference to the
sample water at 20 °C and temperature coefficient is approx. 2.2 %/°C in the range of 0 to 40 °C.
The effect of temperature coefficient on measurement values is compensated by processing
temperature signals from the temperature sensor (Pt 1000 Ω) built in the counter electrode.
In addition to potassium iodide, acetic acid and sodium acetate are added to the reagent to make
the reagent act as a pH buffer. All the chlorine components are effectively detected by reducing
the pH of sample water to 4.5 or below.
For measurement of free available chlorine content, potassium bromide (KBr) is added to sample
water and bromine is liberated by reacting with chlorine as seen in equation (5).
Cl
2
+ 2Br
-
Br
2
+ 2Cl
-
........................................................ (5)
Except for the liberation of bromine, the measurement of free available chlorine is the same as
the measurement of total residual chlorine.
Figure 1.4 illustrates the principle of the RC400G Residual Chlorine Analyzer.
The current flowing between the indicator (ME) and the counter (RE) electrodes is measured
when a specific voltage is applied across the electrodes.
Temperature compensation is implemented through CPU computation based on temperature
signals from the temperature-measuring circuit.
Amplifier
Is
ME
RE
Measuring tank
4 to 20 mA DC,
or 1 to 5 V DC
Voltage-
application
circuit
Temperature-
measuring
circuit
Current/
voltage
conversion
circuit
Current/
voltage
output
circuit
LED
indicator
CPU
F1.4.ai
Counter electrode
Indicator electrode
Figure 1.4 Schematic Diagram of Measuring Circuit
14th Edition : Jul. 15, 2020