18/56
CC1B7865E
February 10, 2000
Landis & Staefa Division
5. Operating modes
Low-fire operation means that only small amounts of heat are drawn from the boiler. A two-
position controller maintains the setpoint, switching the burner on and off like a thermostat.
This control mode is therefore also known as
thermostat function
. An adjustable
switching differential ensures that the switching frequency of the burner can be selected to
reduce wear.
W
HYS1
HYS3
7865w03/1099
Modulating and 2-stage operation:
Actual value between «HYS1» and
«HYS3»
High-fire operation means that large amounts of heat are drawn from the boiler, so that
the burner is on all the time. If the heating load during the thermostat operation rises to a
level where the actual value begins to fall below the switch-on threshold «HYS1», the
controller does not immediately switch over to a higher burner output, but first makes a
dynamic test of the control deviation and only switches to the higher output when an
adjustable threshold «Q» is exceeded (A).
Ö
Section 5.6 «Response threshold Q»
−
In high-fire operation, depending on the application, the burner can be fired in
modulating
or
two-stage
operation, with a larger amount of fuel than in low-fire
operation. The binary input «D1» can be used to switch between modulating and two-
stage operation
−
When the contact is open: modulating burner operation
−
When the contact is closed: two-stage burner operation
In diagram area (1), the thermostat function is active. The modulating mode of burner
operation is shown in area (2). In high-fire operation, a 3-position controller acts on an
actuator through relay 2 (open) and relay 3 (close).
A
B
q
A
q
(2)
(1)
W
HYS1
HYS3
db
7865w07/1099
(3)
In area (3), the actual value exceeds the upper switch-off threshold «HYS3» and the
controller switches off the burner (B). The controller only starts low-fire operation when
the level falls below the switch-on threshold «HYS1» again. If «Q» is exceeded, the
controller switches to high-fire operation (A).
Ö
Section 5.6 «Response threshold Q»
5.1 Low-fire operation
Thermostat function
5.2 High-fire operation
Operating mode
changeover
5.2.1 Modulating burner, 3-position output
