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10.8.2 Operating principle of flow meter
The main components of the flow sensor are:
1. Turbine (with magnet and
counterweight mounted on the
outside)
2. Reed switch (normally open)
3. Magnet
4. Counterweight
Water entering the solenoid valve rotates the turbine (1) and magnet (3), which passes in front of the reed
switch (2), thus closing it. As this contact opens and closes, it generates pulses at a frequency that is a
function of water flow.
The turbine completes 230 revolutions for each litre of water. The operating range of the flow sensor is 0.2-
10 bar.
Using the signal it receives, the microprocessor can calculate the number of litres of water passing through
the solenoid valve.
Mechanical jamming of solenoid valve
The solenoid valve may jam open without being actuated (which will cause flooding if the pressure switch
controlling the water level does not trip). If this occurs, the electronic control system (which continuously
monitors the flow sensor) will lock the door, start the drain pump and display an alarm.
Low water pressure
If the flow sensor does not generate a signal during water fill even though power is being applied to the
solenoid valve, the cause of this condition may be a closed water tap or clogged filter on the solenoid valve
(with consequent low water pressure). If this occurs, a warning will be displayed and the cycle will continue
for five minutes, after which time an alarm will be signalled.
Contact closed Contact open
Signal 0 Signal 1
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