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4. System description
4.1 Function
The SMLC2 low water level limiter works in conjunction with the IGEMA EL030, EL19-2,
EL963, or MS015A/B level probes on the basis of the conductive fill level method of
measurement whereby the electric conductivity of the water medium is used. The conductivity
of the medium is measured in µS/cm. For this method of measurement to function reliably a
minimum conductivity of the substance to be measured is required.
The conductive method of measurement makes two statements: electrode submerged or
electrode emerged or switch point reached or not reached. Before installation the length
(observe thermal elongation) of the electrode must be adjusted to the desired switching points,
e.g. for switching off burner and interrupting the safety circuit.
The limiter determines the current water level (electrode submerged / electrode emerged) in
the boiler. If all conditions for correct operation are met, the safety chain for the steam
generator is enabled (burner can switch on). On detection (level has fallen below minimum
level) the output "pre-alarm" is switched on immediately and the red LED starts to flash (1Hz).
Should this state be present for longer than the alarm delay time set (4s, 8s, 12s, 16s), the
output of the safety chain will be switched off (safe operation mode) and the LED "ALARM"
(red) remains permanently lit.
The factory setting for the alarm delay time is 4s.
To avoid faulty trips, e.g. due to foam or turbulent surface, the detection state is assumed not
before the electrode is permanently submerged for 1,5s.
In the event of a fault (e.g. broken cable, electronics malfunction, ...) the safety chain is
switched off immediately.
Safe operating mode, during which the output contacts of the device go into rest position,
corresponds at the same time to the de-energised state of the limiter.
So that after a fault the burner control does not start up again of its own
accord, manual locking (latching) of the burner must be carried out on
site. It is not a component of the limiter.
Danger
The general function of the limiter SMHL2 is displayed by the lighting of the green LED
"POWER". The input stage of the SMLC2 compares the values of the insulation and the limiter
electrodes. Thus, besides the normal operationg stage, low water detection and triggering of
the insulation surveillance are implemented. Malfunctions of the measuring cable (e.g. short
circuit or cable break) will be detected, too.
The power flowing via the contacts of the safety chain is limited in the SMLC2 by a 4 amp fuse
protection by which sticking of the contacts is prevented.
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