Vaisala WAT12 - Manual (Page 24)

User's Guide ________________________________________________________
22 _____________________________________________________M210309EN-A
The power line is protected against the wrong polarity.
Transient protection is accomplished with VDRs, series
inductors and resistors, and transient zener diodes on both
the power line and each I/O line.
Optional Heating Power
The WAT12 transmitter also provides the sensors with a
throughput for optional heating power. The heating power
connection requires an extra pair of wires. Since the heating
elements, in the shafts of the WAA151 and WAV151
sensors, typically consume some 500 mA, the heating power
is most conveniently supplied from a local power source. A
thermostat switch is available for automatic connection of
the heating power in temperatures below +4 °C.
The optional heating power requirement is 20 VAC or
VDC, and 500 mA for both WAV151 and WAA151
sensors. The sensors can be connected in series, when a
40 V power supply providing 500 mA is required.
Alternatively, the sensors can be connected in parallel, when
a 20 V power supply providing 1 A is required. For the
default connection, refer to Figure 15 below.
0206-053
Figure 15 Default Heating Power Connection with
both Sensors