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Siemens Building Technologies Basic Documentation LMU54... / LMU64... CC1P7494en
HVAC Products 3 Functions 07.11.2002
• Boiler output limitation will be triggered when: Tabgas ≥ TaBegr
• Boiler shutdown will be triggered when: Tabgas ≥ TaAbsch
• Boiler output limitation or shutdown
will be canceled when: Tabgas < TaBegr – SdHzEin
If flue gas temperature supervision responds, an error code or lockout code will be
displayed. In addition, a forced signal will be triggered.
In the case of boiler shutdown, the fan will overrun (ZGebNach).
To ensure that short-time crossings of the flue gas temperature threshold do not
immediately give rise to a response, the acquired flue gas temperature will be filtered
(τ ≈ 2 seconds).
The electronic (S)LT used with the LMU... consists of the following function blocks:
• Switching off in the case of overtemperature
• Conduction of a number of plausibility tests in order to be able to interfere in the
process in due time to avoid overtemperatures
• Conduction of tests in order to detect fault conditions, thus enabling the (S)LT to
initiate adequate actions
Note!
The 2 (S)LT sensors (flow and return) are safety-related sensors!
They must be located and fixed in a way that constant and even heat transfer is ensured
(during the entire occupancy time and also after replacement).
• The flow sensor must be fitted at a location that is representative of the maximum
boiler temperature!
• The return sensor must be fitted at a location that is representative of the return
temperature!
Following must be observed in connection with the flow and return sensors:
• Do not use clamping bands for fixing!
• When using a holding spring, cable strain relief must be provided!
• Screwed immersion sensors can be used without taking any extra measures
Measures may be necessary to check proper heat transfer inside the boiler.
Make certain that parameterization is matched to the specific requirements of
the boiler(s) and plant!
The relevant boiler and plant regulations must be complied with!
We recommend the use of an external safety limit thermostat (connection to LMU-X3-01)
in the following cases:
− Boiler outputs > 120 kW
− Applications involving pressure class 3
The table below contains the faults that can occur. It also shows the related measures,
that is, whether start prevention or immediate lockout shall be triggered.
Electronic (S)LT
Note
Handling faults
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