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Siemens Building Technologies
Basic Documentation LMU54... / LMU64...
CC1P7494en
HVAC Products
3 Functions
07.11.2002
If the pressure sensor is configured, the pressure switch or flow switch will no longer be
checked because water pressure supervision has the higher priority.
Water pressure supervision is overriding boiler temperature control.
When certain threshold values are crossed, the LMU… responds in one of the following
ways:
•
Shutdown (PH2Omax), or
•
Output reduction (PH2Omin), or
•
Shutting down of boiler and pump (PH2OAbschalt)
If water pressure is too high or too low, there will either be start prevention or the unit
will initiate lockout, depending on the parameterization (KonfigRg5).
When water pressure returns to the permitted pressure range, the boiler will be released
with no delay. The following graph shows the various phases of water pressure
supervision:
PH2Omax
Ph2o
7494d33E
PH2Omin
PH2OAbschalt
Time
T 0
T1
T2
T3
T4
T5
T 7
SdPH2O
SdPH2O
T 6
Response =
None
Shutdown
None
*
Boiler
output - 20 %
None
*
None
Shutdown
and pump off
Static water pressure supervision with the LMU...
•
Boiler shutdown will be triggered when:
Ph2o
≥
PH2Omax
•
Boiler output limitation will be triggered when:
Ph2o
≤
PH2Omin
•
Boiler and pump shutdown will be triggered when:
Ph2o
≤
PH2OAbschalt
•
Boiler output limitation or shutdown will be canceled when: Ph2o < PH2Omax – SdPH2O
Ph2o > P SdPH2O
If water pressure supervision responds, an error code or lockout code will be displayed.
To ensure that short-time crossings of the water pressure thresholds do not immediately
give rise to a response, the acquired water pressure will be filtered (
τ
≈
2 seconds).
Static supervision
Function