Landis & Staefa Division CC1B7865E February 10, 2000 27/56
5. Operating modes
The response threshold «Q» defines how long and how low the actual value can drop
before the system switches over 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 for the switching threshold «HYS1». If
the actual value increases, integration is stopped.
If «Q
eff
» exceeds the pre-set response threshold «Q» (can be adjusted at the parameter
level), this causes the second stage of the burner to be switched on or - in the case of a
3-position controller / modulating controller – the regulating unit to open.
If the actual boiler temperature reaches the required setpoint, Q
eff
is set to 0 .
Temperature (°C)
t
HYS1
x
Q
1
Q
2
Q
3
w
Q = 0
eff
7865d19e/1199
Actual value monitoring ensures that the switching frequency is kept low in the
transitional range from low- to high-fire operation in order to reduce wear.
5.6 Response threshold «Q»
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