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Building Technologies Basic Documentation LMV5... CC1P7550en
7 Boiler controller / load controller 22.05.2018
7.8.2 Cold start thermal shock protection – multistage operation
The difference between multistage and modulating control is that with multistage
control, the output steps are defined by the number of burner stages. With modulating
control, any output value in % can be entered.
With multistage control, a maximum of 3 output stages are available:
1. Stage 1
2. Stage 1 and stage 2
3. Stage 1, stage 2, and stage 3
Use of the output stages 2 and 3 can be locked. In that case, the boiler is heated with
stage 1 only.
Parameter Release Stages (release / no release)
When stages 2 and 3 are locked, the system may maintain low-fire operation until the
cold start function is ended, if the output delivered by stage 1 is not sufficient to reach
the switch-off threshold for thermal shock protection.
Spacing of temperature lines
corresponds to the setpoint steps
Manipulated
variable
Actual value
Setpoint
Threshold OFF
Threshold ON
Stage 1
Stages 1 und 2
Stages 1, 2 und 3
Setpoint step is reached
before max. time has elapsed.
Start of 3rd stage.
Max. output will be delivered.
7550d05e/0704
Setpoint step not
reached, but max. time
exceeded.
Therefore, start of 2nd
stage
Burner off,
actual value
below thresh-
old ON.
Burner will be
switched on
⇑
Actual value reached.
Threshold OFF
Change to multistage
control
Figure 62: Cold start thermal shock protection – multistage operation
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