This is the operation obtained by sending an appropriate signal to the air valve servo control so the power sup-
plied by the burner can be of any intermediate value between a preset minimum and maximum.
Continuous modulation is required when boiler water temperature or steam pressure variations must be kept
within restricted limits.
From the diagram, it will be seen that the stop,preventilation, flame formation or switchover to maximum output
phases are the same as those described in the previous paragraph.
Actual flame modulation is obtained by fitting the following devices to the system. These are supplied with an
optional kit:
- Siemens boiler probe, for temperature or pressure.
- Siemens RWF regulator with case for fitting to panel.
- Range adapter for regulator, controlled by the boiler probe and with calibration suitable for the scale of the
probe itself.
DIAGRAM OPERATION CONTINUOUS MODULATION
A
B
B-C
C
LR
C-D
T11 Air shutter opening time, from 0 to max.
TW Begins with the closure of the thermostatic line or the PG. The PA must be in the rest position.
This is thewaiting and self-test time.
T10 Begins when the motor starts up and with the prepurge phase, within which the PA air pressure switch must
give the go-ahead.
T1 Pre-purge time.
T3 Pre-ignition phase, it ends when the gas valve opens.
T2 Safety time, within which the flame signal must reach the EC electrode.
T4 Interval between the opening of the gas valve and the opening of the second stage.
T6 Air shutter closing time and program zero-setting time.
T12 Time in which the air shutter shifts to the start-up position.
UK
Input signals
Output signals
Begin start up
Flame present
Operation
Control stop
Power regolator
Air shutter closure + post-purge
TC-PG Thermostats/Gas pressure switch line
MB
Burner motor
PA
Air pressure switch
TR
Ignition transformer
VE
Gas valve
EC
Control electrode
MT
Air servo control
38