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Building Technologies Division User Manual LMS14... CC1U7471en
6 The settings in detail 07.05.2014
6.11.26 Limitation of output
If the burner’s output is controlled based on the boiler flow temperature, the PID
controller can reduce the burner’s output before the flow temperature reaches the
switch-off point.
If the burner’s output is not controlled based on the boiler flow temperature, but on the
temperature acquired by some other control sensor, the PID controller does not
respond directly to a flow temperature rise.
With stratification storage tanks and instantaneous water heaters e.g., it is not sensor
B2, but some other sensor that is used for control of the boiler’s output in certain cases.
In such cases, it is still necessary to monitor the boiler temperature and to limit the
boiler’s output, or to shut the boiler down, if required. This situation can especially occur
when a heat exchanger integrated in the system is not able to transfer the heat.
To ensure that, in these cases, the PID controller does not push the boiler flow
temperature to a level where the limit thermostat responds, the Output limitation
function can be activated.
Output limitation reduces the burner’s output when the boiler flow temperature reaches
a level lying the parameterized switching differential below the threshold value for
output limitation. As the boiler flow temperature continues to rise, the burner’s output is
constantly reduced until, eventually, it is limited to the minimum when the
parameterized threshold for output limitation is reached. Should the boiler flow
temperature rise above this threshold, the burner is shut down. The burner is switched
on again only after the boiler flow temperature has dropped by at least the switching
differential below the threshold for output limitation.
For practical reasons, the output limitation temperature (Boil temp out red (2527))
should be set to a level below the switch-off threshold of the limit thermostat (Cutout
temp LT (2531)). If set to a higher level, the Reduction function might not be able to
become active since the limit thermostat initiates shutdown before.
Line no. Operating line
2527 Boil temp out red
This parameter is used to set the threshold for limiting the output. The closer the boiler
flow temperature gets to this value, the more the burner’s output is limited. Should the
boiler flow temperature rise above this level, the burner is shut down. The burner is
switched on again only after the boiler flow temperature has dropped by the switching
differential (Swi diff output red (2528)) below this value.
Boil temp out red
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