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Siemens Building Technologies
Basic Documentation RVL471
CE1P2524E
HVAC Products
4 Acquisition of measured values
23.10.2002
4.2.2 Handling
faults
A short-circuit or open-circuit in the measuring circuit is identified and indicated as a
fault. In that case, the plant responds as follows:
•
Plants with 3-position control:
Heating circuit pump / circulating pump M1 continues to run and the mixing valve will
close
•
Plants with 2-position control:
The heating circuit pump / circulating pump M1 continues to run and the burner will
shut down
4.3
Outside temperature (B9)
4.3.1 Measurement
The outside temperature is acquired with the outside sensor. This can be a QAC22 or
QAC32:
•
QAC22: Sensing element LG-Ni 1000
DW&
•
QAC32: Sensing element NTC 575 at 20 °C
The controller automatically identifies the type of sensor used.
In interconnected plants, the outside temperature signal is made available via LPB.
Controllers having their own sensor pass the outside temperature signal to the data
bus.
4.3.2 Handling
faults
If there is a short-circuit or open-circuit in the measuring circuit, the controller responds
as follows, depending on the outside temperature source:
•
Controller not connected to the data bus (LPB):
The control operates with a fixed value of 0 °C outside temperature. An error message
will be generated
•
Controller connected to the data bus (LPB):
If the outside temperature is available via data bus, it will be used. An error message
will not be generated (this is the normal state in interconnected plants!). If there is no
outside temperature available on the data bus, however, the control uses a fixed value
of 0 °C outside temperature. In that case, an error message will be generated.
4.4
Primary return temperature (B7)
4.4.1 Measurement
The primary return temperature is acquired with a sensor having a sensing element LG-
Ni 1000
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primary return temperature and for limitation of the temperature differential (DRT limita-
tion).
In interconnected plants, the primary return temperature with plant type 1–x can be
acquired via data bus. Controllers with plant type 1–0 and connected sensor pass the
return temperature signal to the data bus.
4.4.2 Handling
faults
If there is a short-circuit or open-circuit in the measuring circuit, and if the controller
requires the return temperature, it responds as follows:
