Siemens RVD240 - 4 Acquisition of Measured Values; General; Flow Temperature Heating Circuit; Types of Sensors

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Siemens Building Technologies Basic documentation RVD240 CE1P2384en
HVAC Products 4 Acquisition of measured values 27.05.2004
4 Acquisition of measured values
4.1 General
In the event of a faulty sensor, the RVD240 always attempts to maintain the required
comfort level, if necessary at the expense of certain heat losses. But this will not cause
any damage.
In the case of severe faults, which do not allow the RVD240 to perform its control func-
tions, an error message will be generated. The controller displays this as Er (Error).
4.2 Flow temperature heating circuit
4.2.1 Types of sensors
Suitable are all types of temperature sensors that use a sensing element LG-Ni 1000.
The following types are presently available:
• Strap-on temperature sensor QAD22
• Immersion temperature sensors QAE2...
4.2.2 Handling faults
A flow temperature sensor with a short-circuit or open-circuit always triggers an error
message, irrespective of the type of plant. If that occurs, the heating circuit pump will be
activated and the primary mixing valve driven to the fully closed position in the case of
a mixing circuit, and the heating circuit pump will be deactivated in the case of a pump
circuit.
In all cases, a fault status signal will be generated. This means:
• The controller’s LCD displays Er
• When querying the flow temperature on the QAW70 room unit (if present), its display
shows --- if there is a short-circuit or open-circuit
4.3 Outside temperature (B9)
4.3.1 Types of sensors
The following types of sensors can be used:
• Outside sensor QAC22 with a sensing element LG-Ni 1000
• Outside sensor QAC32 with a sensing element NTC 575, for connection to terminal
B9
The controller automatically identifies the type of sensor used.
The range of use is –50...+50 °C.
The outside temperature can also be acquired via LPB (refer to subsection 20.2.4).
4.3.2 Handling faults
If there is a short-circuit or open-circuit in the measuring circuit of outside sensor
QAC22 or QAC32, the controller will respond as follows:
• Plants with a room temperature sensor:
The controller switches over to room-compensated control
• Plants without a room temperature sensor:
The controller operates with a fixed outside temperature of 0 °C
Note