Vaisala WAC155 - Manual (Page 24)

User's Guide ______________________________________________________________________
22 ___________________________________________________________________M210822EN-A
Optional Heating Power
The WAC155 transmitter also provides the sensors with a throughput
for heating power, which can be connected if sensor heating is required.
The heating power is galvanically isolated from the operating 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 each, the heating power is most
conveniently supplied from a local power source. Unit can
automatically connect heating power in temperatures below +3 °C
(default setting).
There are two ways to connect the heating power, depending on the
heating power supply available. The default way is to connect a 40 VAC
or VDC power supply in series; see
Figure 10 on page 22 . When a 40 V
power supply is used, 500 mA is required. The 40 V power supply can
only be used when both sensors are connected.
0702-014 Figure 10 Heating Power Connection with 40 V Power Supply
If a 20 VAC or VDC power supply is used, the heating power should be
connected in parallel. The power supply must provide 500 mA for each
connected WAV151 and WAA151 sensor; 1 A is required when both
NOTE If you connect DC heating power, observe the correct polarity of the
X2 connector pins 1 and 2 (HT1+ and HT2-).