Vaisala WMT700 - Manual (Page 84)

User's Guide ______________________________________________________________________
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
- Heating for body, transducers, and array arms
NOTE Ensure that the supply output power capacity is high enough especially
when transducers, array arms, and sensor body 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.
When heating voltage falls below 18 VDC, an alarm is raised.
Heating is automatically disabled if heating voltage falls below 15
VDC.
Regardless of heating voltage, the maximum heating power is
limited to 40 W and the average heating power is limited to 30 W.
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) scheme is used to control the
average heating power.
82 ___________________________________________________________________ M211095EN-E