Vaisala WAC155, User Manual

Page: 21 / 58

The heating power connection requires an extra pair of wires. Since the required heating
current for the WA15 series is typically 0.5 ... 1 A, it is most conveniently supplied from a local
power source. WAC155 automatically connects heating power in temperatures below +4 °C
(39.2 F).
There are two ways to connect the heating power, depending on the heating power supply
available. The default way is to use a 40 V power supply and connect the heating elements of
the sensors in series.
When connecting DC heating power, make sure you have the correct polarity of
the X2 connector pins 1 and 2 (HT1+ and HT2-). AC heating power wires can be
connected either way round.
You can use the 40 V power supply only when both sensors are connected. The sensor heating
elements have a 40 Ω resistance each. The typical heating current is 0.5 A in a series-
connected system with a 40 V power supply.
Figure 9 Heating Power Connection with 40 V Power Supply
If you use a 20 V power supply, you must connect the sensor heating elements in parallel. The
following figure shows the parallel connection. In this case, the typical current demand is 0.5 A
+ 0.5 A = 1 A.
Chapter 3 – Installation
19