Gill Instruments Ltd
_____________________________________________________________________________________________________________
________________________________________________________________________________________________
WindObserver 65
Page 44
Issue 4
Doc. No. 1390-PS-0039
June 2016
Polar mode direction wraparound
The Wind Direction in Polar mode can be configured for either Standard (0 - 359
) or
Wraparound (0 - 539
)
options. If the Standard mode is used with a chart recorder, large
swings of the recorder pen will be experienced each time the wind direction passes
between 0 and 359
. Using the Wraparound mode, when the wind first changes from 0
to
359
, there will be a step change on the output, but after this first time the output will
change smoothly each time the wind passes through 360
. (Similarly, the first time the
wind veers from 539
to 180
, there will be a step change, after which the output will
change smoothly).
Wind
direction
(degrees)
Voltage output (V)
Current output (mA)
Standard
Wraparound
Standard
Wraparound
0
0
0
4.00
4.00
180
2.5
1.67
12.00
9.33
360
5.0
3.33
20.00
14.67
540
N/a
5.0
N/a
20.00
Low wind speeds
Whilst the wind speed is below 0.05 metres/sec, the wind direction will not be calculated,
all other output parameters will continue to update at the output rate.
The following Table shows Channel 1, 2 and 3 outputs with Polar Continuous, 4-20mA
current outputs under various operating conditions. Status channel 3 output also shows
conditions when 0-5v or ±2.5v outputs are used.
Condition
Channel 1
(Wind Speed)
Channel 2
(Wind Direction)
Channel 3
(4-20mA
Status)
Channel 3
(0-5v
Status)
Channel 3
(±2.5v
Status)
Wind Speed,
Greater Than
0.05m/s
Variable 4 to
20mA (value
depends on
Output scaling)
Variable 4 to 20mA
(Value depends on
Output scaling)
4mA
(Unit
functioning
correctly)
0v
(Unit
functioning
correctly)
-2.5v
(Unit
functioning
correctly)
Wind Speed,
Less Than
0.05m/s
Variable close
to 4mA.
Outputs last known
good/valid current
reading until wind
increases above
0.05m/s.
4mA
(Unit
functioning
correctly)
0v
(Unit
functioning
correctly)
-2.5v
(Unit
functioning
correctly)
Any Wind
Speed with
Failure Codes
Output 01, 02,
04 etc.
Fixed 4mA
until fault
clears.
Outputs last known
good/valid current
reading until fault
clears.
0mA
(Failure code
present)
5v
(Failure
code
present)
+2.5v
(Failure
code
present)
Cables.
If using 4-20mA outputs then cable length is limited to the resistance of the connecting
cable (to and from the load) plus the load resistance which all together must be less than
300 ohms.
If using 0-5v output then consider volt drops on the cable that might impact on 0v and 5v
readings. A 4-20mA system will be more noise immune and capable of longer cable runs.
