Operating And Control Principles - Carel heaterSteam User Manual

ENG

4.4 Operating and control principles

Before describing each electrical connection on heaterSteam, below are
some fundamental aspects regarding the control of steam humidifi ers.
4.4.1 Operating principle of a heater humidifi er
HeaterSteam is an isothermal steam humidifi er whose technology uses
heaters immersed in a cylinder or boiler fi lled with water. This may be
mains water or demineralised water. The heat generated by the heaters
increases the water temperature up to around 100°C (212°F). The use
of demineralised water ensures long cylinder and heater life, as virtually
no scale builds up. On the other hand, if using mains water, some of the
minerals dissolved in the water accumulate in the cylinder as solids with
diff erent compositions. To prevent this from occurring, when the water
conductivity in the cylinder exceeds a certain value, some of the water is
periodically drained and replenished, thus diluting the water. In models
where featured, the drain water is mixed with mains water so as to not
exceed the maximum temperature allowed by national and local standards
in force (drain tempering function). The steam generated has a temperature
of around 100°C (212°F) and minimal positive pressure (unpressurised
steam). It is virtually free of minerals and germs. Steam production is
controlled with ON/OFF logic or with continuous modulation from 0% to
100% of rated output, using solid state relays (SSR); the control logic in this
case is PWM (i.e. pulse width modulation) with a programmable time base.
4.4.2 Control principles
The appliance is fi tted with solid state relays (SSR), meaning steam
production is continuously adjustable based on demand, in one of the
following modes.
4.4.3 ON/OFF control
Operation is all or nothing, and is activated by an external contact; the
maximum percentage of unit production can be set.
4.4.4 Proportional to an external signal (modulating
control)
Steam production is proportional to the value of an external signal Y,
(selectable by programming one of the following standards: 0 to 1 Vdc; 0
to 10 Vdc; 2 to 10 Vdc; 0 to 20 mA; 4 to 20 mA). The maximum production
Pmax corresponds to the maximum value of the external signal Y and
will be the humidifi er's rated production. The activation hysteresis hy is
settable by the user and refers to the external signal Y.
P
max
Steam_Pr
P
min
OFF
0%
hy
Key:
Steam_pr Steam production
P0 Max production
Pm Min production
Note: the graph shown above applies when the pre-heating
function is disabled.
"heaterSteam" +0300080EN - rel. 1.0 - 27.04.2016
Y= 0...1Vdc
0...10Vdc
2...10Vdc
0...20mA
ON
4...20mA
Y
2xhy 100%
Fig. 4.l
Y External signal
hy Activation hysteresis
4.4.5 Autonomous control with humidity probes
Steam production is related to the % rH reading made by the relative
humidity probe and increases as the value read deviates from the set
point St. Maximum production Pmax corresponds to the case where the
humidity value, read by the probe, is BP away (proportional band) from
the set point. The activation hysteresis hy is settable by the user.
P
max
Steam_Pr
P
min
Key:
Steam_pr Steam production
P0 Max production
Pm Min production
To check that the relative humidity measured by the transducer is within
certain preset values, two alarm thresholds can be set in autonomous
control:
•
high relative humidity alarm threshold;
•
low relative humidity alarm threshold.
When these thresholds are exceeded, an alarm is activated by closing the
corresponding relay contact on the main control board.
4.4.6 Autonomous control with relative humidity
transducer and outlet limit probe
In this case too, the controller modulates steam production based on the
% rH measured by the main relative humidity transducer, while limiting
production if the humidity measured by a second limit transducer,
located in the air duct downstream of the steam distributor, approaches
the maximum desired value. Consequently, to prevent the relative
humidity of the outlet air from exceeding a value that is considered
excessive, the control module with autonomous control and limit
transducer can be set with a high relative humidity alarm threshold.
When this threshold is exceeded, the alarm is activated by closing the
corresponding relay contact on the main control board. The limit probe
allows steam production to be modulated depending on the specifi c set
limit diff erential.
4.4.7 Application for steam baths
In applications for steam baths, in which the control probe measures
temperature rather than humidity, the same rules apply as for
autonomous control with probe.
By setting control to temperature, the humidifi er will continue to produce
steam until reaching the desired set point temperature inside the steam
bath, and consequently the desired saturation of the air (fog eff ect).
Recommended CAREL transducer: ASET030001 or ASET030000, or NTC
probes UEKNTC0*.
20
ON
OFF
hy
%rH
BP
St
Fig. 4.m
Y External signal
hy Activation hysteresis