Power management – Vaisala WXT520 User Manual
Page 53
Chapter 5 _______________________________________________ Wiring and Power Management
VAISALA_______________________________________________________________________ 51
Note that the RS-485 interface can be used as well with four wires (as
the RS-422). The basic difference between the RS-485 and RS-422 is
actually their protocol. Namely, in the RS-422 mode the transmitter is
held constantly enabled, while in the RS-485 mode it is enabled only
during transmission (for allowing the host’s transmission in the two-
wire case).
The RS-232 output swings only between 0 ... +4.5 V. This is enough for
modern PC inputs.The recommended maximum for RS-232 line length
is 100 m (300 ft) with 1200 Bd data rate. Higher rates require shorter
distance, for instance 30 m (100 ft) with 9600 Bd.
Power Management
The power consumption of the WXT520 varies significantly, depending
on the selected operating mode or protocol, the data interface type, the
sensor configuration, and the measurement and reporting intervals.
Lowest consumption is achieved with the Native SDI-12 mode,
typically about 1 mW in standby (0.1 mA @ 12 V), while with ASCII
RS-232 or Continuous SDI-12 modes it is about 3 mW in standby. Any
sensor measurement, while being activated, adds its own extra
consumption to the standby power.
Some hints for economic power management are given below. The
current consumption values are all defined for 12 V supply. For 6 V
supply, multiply the values by 1.9. For 24 V supply multiply the values
by 0.65 (see
-
Wind measurement is absolutely the most consuming operation
in the system. So, it all depends on how the wind is to be reported.
If long time averages are needed, the wind must be constantly
measured - then it makes no big difference, which requesting
period or mode is used. Fully continuous wind measurement with
4 Hz sampling rate adds 2 ... 5 mA to the standby current
(depending on the wind and some other climatic conditions). But
for instance 10-second average requested every 2 minutes
consumes 12 times less. And 1 Hz sampling rate makes it further
decrease to one fourth.
NOTE
If you use the WXT520 on an RS-485 bus with other polled devices,
always disable the error messaging feature. You can do this with the
following command: 0SU,S=N<crlf>.