Power management – Vaisala WMT52 User Manual
Page 49
Chapter 5 _______________________________________________ Wiring and Power Management
VAISALA_______________________________________________________________________ 47
The termination resistors will remarkably increase power consumption
during data transmission. If low power consumption is a must, a 0.1
μ
F
capacitor needs to be connected in series with each termination resistor.
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 WMT52 varies depending on the
selected operating mode or protocol, the data interface type, 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.
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
NOTE
When WMT52 is used on an RS-485 bus with other polled devices, the
error messaging feature shall always be disabled. This is done by the
following command: 0SU,S=N<crlf>.