Data
76
Effect of flow rate
Sensitivity of residual chlorine monitor with the polarographic method is affected by the flow
rate on the surface of the cathode electrode.
The gradient of concentration in the diffusion layer that is relational to the sensitivity is
dependent on the flow rate.
For the stable measurement, it is necessary to supply new sample to the cathode constantly
for keeping stable gradient of concentration on the cathode.
The RA-10 over flow type sensor reduces the fluctuation of flow rate to the cathode electrode
by the head tank even the inlet flow rate varies.
It is necessary for the in-line sensor (RA-20) to use a constant flow valve to keep flow rate
constant.
Fig. 5 Changes in the reading depending on the flow rate of the sample (for the RA-20)
Note
Correct reading is achieved on the assumption of the constant and proper flow rate.
Effect of sample temperature
In the polarographic method used by the HR-200, the signal from the sensor is affected by the
temperature of the sample.
There are two main reasons of the temperature dependency.
(1) The thickness of the diffusion layer on the cathode surface is dependent on the
temperature of solution.
(2) The chemical equilibrium of the hypochlorous acid and hypochlorous ion is dependent on
the temperature of solution.
The HR-200 compensates the signal affected by the temperature of the sample with a function
canceling the phenomena.
Sample flow rate [mL/min]
Sensitivity vari
ation
rate
at 8
00
mL
/min
ratio
[
]
160
140
120
100
80
60
40
20
0
400
600
1000
1200
800
h19136 | UTC 2020/03/30 3:34:51
CONFIDENTIAL
