Bosch SSB1000 SA, Manual, Page: 11 / 84

SSB 6720892984 (2019/02) US
BURNERS cascade | 11
The following diagram shows how the setpoint to the dependents is determined:
T_System
Cascade setpoint
Burner Power
T_Supply sensor
T_Supply sensor
PID
PID
System Loop
Burner Power
Offset Setpoint
Calculation
Calculated boiler setpoint
Calculated boiler setpoint
PID
Dependent 1 boiler
PID loop
Dependent 2 boiler
PID loop
PID slew rate
The changes of the PID output can be limited with the
PID_Slew_Rate_Step_Up and PID_Slew_Rate_Step_Down
(factory settable) setting to
avoid big setpoint changes to the burners. The slew rate is set in °C/100ms.
For example when the
PID_Max_Slew_Rate_Up
and
PID_Max_Slew_Rate_Down
are set to 1,0°C/100ms it means the calculated setpoint can
change a maximum of 1,0°C every 100ms.
The slew rate can be set in steps of 0,1°C/100ms. When set to 0,0°C/100ms the limitation is disabled.
Dependent Burner
The CH mode for the cascade is defined by the setting of the managing burner. CH mode settings on dependents are ignored.
In case a burner is set as dependent (Address = 2-8/16) the setpoint is always provided by the managing burner.
The modulating power of the ALL burners is PID controlled by the burner itself by comparing the calculated setpoint from the managing burner and
T_Supply
.
The burner of the managing burner itself will be controlled in the cascade system as it would as it was a dependent burner.
Only the pumps and sensor inputs are used.
Burner power
Cascade operation with power modes is designed to work best in cascade systems with equal burners/burners having the same power output.