HVAC Products CC1B7865en 05.12.2002 27/57
5. Operating modes
The response threshold «Q» defines for how long and how low the actual value is
allowed to drop before the system switches to high-fire operation.
An internal mathematical calculation using an integration function determines the sum of
all the areas Q
eff
= Q1 + Q2 + Q3, as shown in the diagram. This only takes place when
the control deviation (x-w) falls below the value of the switching threshold «HYS1». If
the actual value increases, integration is stopped.
If «Q
eff
» exceeds the preset response threshold «Q» (can be adjusted on the parameter
level), this causes the second stage of the burner to switch on or - in the case of a
floating controller / modulating controller – the actuating device to open.
If the actual boiler temperature reaches the required setpoint, Q
eff
is reset to 0 .
Temperature (°C)
t
HYS1
x
Q
1
Q
2
Q
3
w
Q = 0
eff
7865d19e/1199
Monitoring of the actual value ensures that the switching frequency is kept low in the
transitional range from low- to high-fire operation, aimed at reducing wear.
5.6 Response threshold «Q»
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