41
Operation
Calibration
Before calibration, for the first time, it is necessary that the instrument has been connected
to power supply and has been measured for at least 30 min.
The calibration is performed against solutions with known chlorine concentration, by
DPD1. It is recommended to calibrate weekly. For calibration, follow the instructions in
4.9.3 Calibration, page 39.
Measurement.
The simple flow should be 90-100 L/h.
Alarm relay
When the flow interrupts, the sensor reading drops sharply. MultiMeter 44 has a
programmable alarm relay suitable for avoiding excessive chlorine during the flow
interruption.
Regulation delay
It is recommended to program a value of 30 min as a regulation delay, see 4.4.2
Configuration modification, page 22. In this way excessive chlorine will be avoided
meanwhile the sensor is not 100% operating. During the delay time the limit relays are
open and the alarm disconnected.
Chlorine measurement with redox electrode
It is necessary to connect a redox electrode, see 4.9.1 Connections, page 36.
The measured value in mV by the electrode will be displayed.The values of limits and
alarm must be programmed in mV.
4.9.6 Chlorine measurement. A little theory
Mainly products containing chlorine are use for chemical treatment of water. All these
products produce hypochlorous acid when reacting with water. The amount of
hypochlorous acid depends directly on pH.
In water with high pH, the majority of this acid (active chlorine) is converted in hypochlorite
ion with very low disinfecting power.
These two forms of chlorine are in equilibrium depending on the pH values.
Figure 21 Chlorine graphic
At pH< 2 the chlorine is in form of molecular Cl
2
At pH 5 the molecular chlorine disappear and appears the HClO
At pH>10 the chlorine is in form of OCl
–
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