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13. OPERATING PRINCIPLES
13.1 Ultrasonic atomisation
Ultrasonic humidifiers produce mist through propagation of a wave
generated by a piezoelectric element to the surface of the water.
Droplets of water that form on the surface, with the smaller ones being
carried air by the forced air flow. The quantity of mist depends
on water level, water temperature and distribution in the air.
Water level is kept constant using fill and drain valves, and a level sensor.
DI water is recommended: if using any other type water, scale
that accumulates over time will foul the piezoelectric transducer,
affecting operation. To avoid excessive scaling, humidifier periodically
drains and automatically refills the water (periodical washing).
13.2 Control principles
The humidifier can be controlled using the following signals:
•
remote ON/OFF;
•
TAM (set by dipswitch);
•
Humidity probe (set by dipswitch);
•
Serial.
ON/OFF control
The action is all or nothing, activated by an external contact that
consequently determines the control set point and differential. The
external contact may be a humidistat, whose status determines the
operation of the humidifier:
•
contact closed: the humidifier produces water vapour if the remote
ON/OFF contact is also closed;
•
contact open: water vapour production ends.
Proportional control (only with auxiliar card)
•
Water vapor production is proportional to the value of a signal “Y”
from an external device. The type of signal can be selected between the
following standards: 0 to 10 Vdc, 2 to 10 Vdc, 0 to 20 mA, 4 to 20 mA
•
Maximum humidifier production, corresponding to the maximum
value of the external signal, can be set from 10% to 100% of the rated
value of the humidifier (parameter P0).
Minimum production has an activation hysteresis, equal to the value of P1
(default 5% of the proportional band of external signal “Y”).
ON
OFF
P1
P1
P0
10%
Y
Produzione di vapore
Steam production
Fig. 13.a
Automatic control with humidity probe
Humidity production is controlled based on the reading of the relative
humidity probe (TH or connection via optional card).
The humidifier will produce until reaching the set point (St, default 50
%rH), with a settable activation hysteresis (P1 default 5%) (see the figure)
to maintain the set point.
P0
% rH
P1
P1
St
Produzione di vapore / Steam production
Fig. 1.a
13.3 Flow-rate modulation
Water flow-rate can be varied from 5% to 100% (parameters Pm and
P0) by alternating on-off cycles of the transducers over a set period
(parameter b7, default 1 second).
Flow-rate is set based on parameter P0 (default 100%) and the request
from the external signal (with optional card and proportional control).
ON
t
OFF
Periodo (b7)
Trasduttore / Transducer
Portata 10%
Fig. 13.b
ON
t
OFF
Periodo (b7)
Trasduttore
Transducer
Portata 50%
Fig. 13.c
ON
t
OFF
Periodo (b7)
Trasduttore
Transducer
Portata 75%
Fig. 13.d
If the flow-rate is 100%, the transducers are always on.
Mist Production
Transducer
Flow 10%
Transducer
Flow 50%
Transducer
Flow 75%
Mist Production
