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DESCRIPTION OF TWO-STAGE
PROGRESSIVE OPERATION
Blown air burners with electronic modulation may be used on
hearths under strong pressure or in a vacuum, according to the
corresponding operating curves. They combine a very stable flame
with total safety and high performance.
The burner is equipped with a LAMTEC electronic cam model
"BT 3xx" controlled by a microprocessor with intermittent operation,
to control and monitor blower gas burners with electronic modulation
by means of two regulating motors (air/gas). During operation as
automatic burner, a valve tightness control is also incorporated. To
better understand the operation of the "BT 3xx" electronic cam, read
carefully the instructions in the attached manual.
The term two-stage progressive operation indicates that transition
from the first to the second state (from minimum to maximum
operation) is progressive in terms of both amount of combustion
air let in and the amount of output fuel. This results in a greater
pressure stability in the gas supply network. Ignition is preceded
by the combustion chamber pre-ventilation (as set forth by the
Standards), with air open and with a duration of approx. 30 seconds.
If the air pressure switch has detected a sufficient pressure, the
ignition transformer activates at the end of the ventilation phase
and after 3 seconds the safety and main valves open in sequence.
Gas reaches the combustion head, mixes with air supplied by the
fan and is ignited. The gas supply is regulated by the butterfly gas
valve. Three seconds after the valves (main and safety) activate,
the ignition transformer switches off. Thus the burner is ignited at
2
the ignition point (
). The presence of the flame is detected
by the control device (ionisation probe immersed in the flame).
The programmer relay moves past the locking position and sends
voltage to the air/gas supply adjustment servomotors, which go
to the minimum point (200). If the second stage boiler thermostat
(or pressure switch) allows it (set to a temperature or pressure
value higher than the existing value in the boiler), the air/gas
supply servomotors will start to turn, gradually increasing gas and
combustion air supplies up to the maximum supply to which the
burner has been set (999).
The "BT 3xx" electronic cam commands the burner, activating
the combustive air and gas servomotor on the basis of a
pre-set curve.
The burner remains in the maximum supply position until the
temperature or pressure has reached a sufficient value to cause
the second stage boiler thermostat (or pressure switch) to trip,
which makes the air/gas supply adjustment servomotors turn in the
opposite direction to the previous one, gradually reducing gas and
combustive air supply until the minimum value.
If the threshold value (temperature or pressure), to which the
complete shutdown device (thermostat or pressure switch) is set,
is reached even with minimum gas and air output, the burner will
be shut down when the device is triggered. As the temperature or
pressure drops below the shut-down device's set point, the burner
will be turned on again as described above.
During normal operation the second stage boiler thermostat (or
pressure switch) applied to the boiler detects variations in demand
and automatically adapts fuel and combustion air supplies, activating
the air/gas supply adjustment servomotors with increasing or
decreasing rotation. This causes the air/gas supply control system
to balance the amount of heat supplied to the boiler with the amount
it gives off during use.
If a flame does not appear within three seconds from the opening
of the gas valves, the control equipment will lockout (shutting down
the boiler completely and showing the corresponding error message
on the display (3)).
To "unlock" the equipment, press the RESET button (4) for about
half a second.
DeTaiL Of BUTTerfLY VaLVe fOr gas fLOW
regULaTiOn BY means Of serVOmOTOr
A
Butterfly gas valve position reference index.
B
Gas modulation servo motor.
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0006160034_201307
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