W3T331759 / WT.050.585.003.UE.IM.1014
29
MICRO/2000® AND DEOX/2000® MODULE
3.2.1 MICRO/2000® and DEOX/2000® flow block assembly
MICRO/2000® and DEOX/2000® Flow Block Assembly - 3
Electrode Measurement for Total and Free Cl2, ClO2, O3, or KMnO4
(MICRO/2000®), Total Cl2 and SO2 or NaHSO3 (DEOX/2000®).
A sensor module (“DES” for 3 electrode cells) and terminal strips are used
to connect the MICRO/2000® and DEOX/2000® flow block assembly
to the SFC. Various controller function are available depending on the
application selected.
3.2.1.1 MICRO/2000® flow block theory of operation
The measurement of free chlorine is made directly at a buffered pH of 4
with pH 4 buffer. The measurement of total chlorine is made by reacting
the various chlorine species with potassium iodide at the buffered pH, then
measuring the resulting iodine concentration.
The net reaction of chlorine with iodide is:
Cl
2
+ H
2
O
-
> 2H
+
+ OCl
-
+ Cl
-
(hydrolysis of chlorine)
OCl
-
+ 2I
-
+ 2H+ -> H
2
O + Cl
-
+ I
2
The analyser measuring process is as follows:
A continuous sample is delivered to the analyser. A flushing Y-strainer
divides the sample into two streams—the larger bypass stream continuously
flushes the Y-strainer and the smaller stream, about 500 ml/min, flows
into the analyser. Most of the flow into the analyser is again bypassed,
but a small portion (15 ml) is metered from this flow by a peristaltic
metering pump. The reagents, pH 4 buffer for the measurement of free
chlorine residual and potassium iodide solution for the measurement of
total chlorine residual, are also metered by the same pump. The reagents
are then mixed with the sample as the sample is pumped to the analyser
cell. A three-electrode amperometric “probe” is immersed in the sample
in the cell. A rotating impeller stirs the sample and maintains a constant
sample velocity across the electrode surfaces. It also agitates the grit
used to clean deposits from the electrodes, improving the stability of
calibration. The amperometric cell produces a signal (electrical current)
proportional to the oxidant (e.g., chlorine) concentration in the cell.
Содержание WALLACE & TIERNAN DEOX/2000
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