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4.1.2.2. Handling of faults
4.1.3. Outside temperature (B9)
4.1.3.1. Measurement
4.1.3.2. Handling of faults
4.1.4. Primary return temperature (B7)
4.1.4.1. Measurement
4.1.4.2. Handling of faults
Siemens Building Technologies
Landis & Staefa Division
A short-circuit or interruption in the measuring circuit is identified and displayed as a
fault. In that case, the plant will respond as follows:
•
Plants with mixing valve control:
The heating circuit pump/circulating pump M1 continues to run and the mixing valve
will close
•
Plants with boiler control:
The heating circuit pump/circulating pump M1 continues to run and the burner will
shut down
The outside temperature is acquired by the outside sensor, which may be a QAC22 or
QAC32:
QAC22: sensing element LG-Ni 1000 Ω at 0 °C
QAC32: sensing element NTC 575 Ω 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.
If there is a short-circuit or an interruption in the measuring circuit, the control will re-
spond as follows:
•
In the event of a short-circuit:
If an outside temperature is made available via LPB, it is used. If none is available, the
control uses a fixed value of 0 °C outside temperature. A fault status signal is always
generated
•
In the event of an interruption:
If the controller requires an outside temperature and it is made available via LPB, it is
used. There will be no fault status signal in that case (this is the usual status in inter-
connected plants!). If, however, there is no outside temperature made available via
LPB, the control uses a fixed value of 0 °C. In that case, a fault status signal will be
delivered
The primary return temperature is acquired with a sensor having a sensing element LG-
Ni 1000 Ω at 0 °C. This measured value is required for minimum and maximum limita-
tion of the primary return temperature and for limitation of the temperature differential
(DRT limitation).
In interconnected plants, the primary return temperature with plant type 1 can be ac-
quired via the data bus. Controllers with plant type 1 and connected sensor pass the
primary return temperature signal to the data bus.
If there is a short-circuit or an interruption in the measuring circuits, the control will re-
spond as follows:
•
If, on the data bus, there is a return temperature from a controller of the same seg-
ment available, it is used (only with plant type no. 1). No fault status message will be
generated since this is the normal status in inconnected plants
•
If, on the data bus, there is no return temperature available, the return temperature
limitation functions will be deactivated and a fault status message generated
Basic Documentation RVL470
Acquisition of measured values
CE1P2522E / 30.03.2000
11/68
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