Level Control; Working Level Switch; Safety Level Switch; Overfill Device - Carel heaterSteam User Manual

2.1 Level control

Steam is produced with the heating elements completely immersed in the water, the level of which is controlled by a sensor
made up of two independent and overlapping float switches, that is the working level switch and safety level switch.
The level control, housed in a transparent case to allow visual inspection, communicates with the cylinder through special
tubing; a second tube, attached to the cylinder cover , equalises the pressure.

2.1.1 Working level switch

This switch, which activates the fill electrovalve, introduces water through the special tubing into the fill tank, from where,
dropping from a fill diaphragm, it refills the level inside the cylinder; the fill electrovalve is fitted with a flow limiter,
maintaining the flow basically constant on changes in mains pressure.

2.1.2 Safety level switch

This switch shuts off power to the elements, activating the alarm in the case where the level is insufficient.

2.2 Overfill device

This is a device used to avoid water exiting the cylinder over the safety level, due for example to the malfunctioning of the
control module (for more details, see THE HUMIDIFIER CONTROLLER) or to leaking from the fill electrovalve.
The fill tank is fitted with an overfill diaphragm which deviates the excess inlet water, discharging it through special tubing.
The overfill diaphragm is lower than the fill diaphragm to avoid back flow through the supply tube.

2.3 Regulation of steam production

Steam production can be regulated either:
By step, alternating steam production with standby using a humidistat or external contact; steam production can be
regulated in four steps with pseudo-modulation from 30% to 100% of nominal power, cyclically activating the remote-
control switch (humidifier with type C control module).
By continuous modulation from 0% to 100% of nominal power, using solid state relays (SSR); the regulation logic is PWM
(variation of the length of the impulse) with programmable base times (humidifier with type H or T control module).

2.4 Measurement of the conductivity of the supply water - alarm thresholds

To optimise the functionality of the humidifier by suitably portioning the automatic draining cycles (see Automatic draining),
when the fill electrovalve is opened the conductivity of the inlet water is measured using the special electrodes in the fill tank.
Two high conductivity thresholds can be set to activate respectively a pre-alarm and an alarm (with the shut-down of the
appliance) when these thresholds are exceeded for at least 60 minutes, or instantly if the value measured is greater than three
times the set value.

2.5 Automatic draining

The automatic draining function is handled by the control module. Part of the water contained in the cylinder is drained
automatically, being replaced by fresh water to prevent an excessive salt concentration following the evaporation process.
The drain electrovalve is opened for a pre-set time at intervals which vary automatically as a function of the steam production
and the content of solids dissolved in the supply water, detected using the conductivity measuring electrodes.
Irrespective of the concentration of salt in the supply water, at least one draining cycle is performed within a maximum
interval based on the quantity of steam produced; this is also true for demineralised supply water.

2.6 Foam elimination procedure

The level of water inside the cylinder is maintained by the level control at around 10-12cm from the top of the cylinder, and
thus, when the high level electrodes are wet, an anomalous situation arises, generally caused by the presence of foam. In this
case a drain procedure is activated, and is repeated until the phenomenon desists or, in the event of multiple activation, until
the appliance is shut-down and an alarm state is signalled.

2.7 Safety thermostat

The mechanical safety thermostat with manual reset intervenes in the event of overheating, caused by a lack of water inside the
cylinder due to the malfunctioning of the minimum level control. This deactivates the relay that controls the power supplied to
the elements, and places the humidifier in an alarm state.
Carel code +030221761
5
preliminary version - rel. 2.0 - 03/09/99
heaterSteam