Operating Manual
Smart Weather Sensor
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany
27
8.1.1
Limitations in 12V mode
If the heating is operated on 12V DC, account must be taken of the functional restrictions in
winter operation.
Note:
A heating voltage of 24V DC is recommended to guarantee full heating duty.
8.1.2
Limitations in Case of Operation with Supply Voltage Below 12V
When operating a Smart Weather Sensor (device version >= 037) with supply voltages lower
than 12V DC, the fan will be not switched on, independent of the fan operating mode. This
may influence the accuracy of temperature and humidity measurement in case of solar
radiation.
Additionally deviations of the compass measurement values have to be accepted.
When operating the Smart Weather Sensor in Power Save Modes with supply voltages
below 12V the minimal supply voltage depends on the length of the connection cable.
The minimal permitted supply voltage (U
Bmin
)can be approximately evaluated from the
equation:
U
Bmin
= 4V + 0.3V (cable length / m)
The minimal supply voltage for a 10m cable is then U
Bmin
= 6V. The influence of the cable
length on minimal supply voltage can be reduced by using of a cable with larger wire cross
section.
8.2
RS485 Interface
The equipment has an electrically isolated, half-duplex, 2 wire RS485 interface for
configuration, measurement polling and the firmware update.
See page 43 for technical details.