User`s guide

Chapter 4 _______________________________________________________________ Installation
VAISALA _______________________________________________________________________ 57
Heating
WMT700 can include a heating functionality that ensures proper
operation in cold environmental conditions or in cases where snow and
ice build-up is possible.
In addition to the standard non-heated version, WMT700 can be
preconfigured at the factory according to your order:
- Heating for the transducers only
- Heating for both transducers and array arms.
NOTE
Ensure that the supply output power capacity is high enough especially
when both transducers and array arms are equipped with heaters.
Also, note that there are individual connections for applying the heating
voltage.
Heated Transducers
The heating functionality has a thermostatic control with temperature
sensors in each transducer. The control function keeps the transducer
temperature above 0 °C and adds heating power when necessary.
Therefore heating is only activated when there is a risk of ice build-ups.
If a sensor is blocked, WMT700 increases the heating power to melt the
ice and returns to lower power after a period of time.
You cannot change the heating parameters, but you can enable or disable
the heating functionality with configuration parameters. Heating is
automatically disabled if the heating voltage falls below 12 VDC.
Regardless of the heating voltage, the maximum heating power is limited
to 40W and the average heating power is limited to 30W. The maximum
power control is achieved by automatically sequencing the transducer
heaters depending on a heating voltage. At low heating voltages, all the
transducers are heated simultaneously. At mid-range, two of the
transducers are heated. At high voltage end, a single transducer is heated
at a time. A PWM (Pulse Width Modulation) is used to control the
average heating power.