User Guide M211095en-h



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‣ Analog Output Signal for Wind Speed Channel (page 21)
3.3 Wind Speed and Direction Averaging
WMT700 provides average values for wind speed and direction using either scalar or vector averaging. With both methods, the average is determined according to the user- configurable averaging time. The averaging time affects serial communication and analog output similarly.
You can also configure the gust averaging time for calculating wind extreme values. The default gust averaging interval is 3 seconds, as recommended by World Meteorological
Organization (WMO).
If you select scalar averaging, you can also enable wind direction coasting to ensure consistent direction measurement results at low wind speeds.
Chapter 3 – Functional Description
35


3.3.1 Scalar Averaging
When you select scalar averaging, WMT700 calculates wind speed and direction averages by adding up each wind measurement from the averaging time and dividing the sum by the number of measurements. The time between each consecutive wind speed and wind direction measurement is 0.25 seconds.
Wind direction is a circular function with a discontinuity at North, where 360° is equal to For example + 5° = + 4°
0° - 5° = 355°
WMT700 translates wind direction to a linear function to determine the wind direction average. For example + 5° is translated to 364°, which is then further converted to +4° for output - 5° is translated to This ensures that the wind direction average stays representative of the true situation even if individual samples occur on both sides of the zero direction.
If the data acquisition system requests data before the initial averaging time completes, the sensor returns the most recent complete measurement data.
The following figure shows an example of averaging wind direction when the measured wind values are 355° and 10°. The resulting average is 2.5°.
WMT700 User Guide
M211095EN-H
36

Figure 15 Example of Wind Direction Averaging Wind Direction Coasting
Accurate wind direction measurement requires that the wind speed is sufficient. If you enable wind direction coasting, WMT700 does not calculate wind direction when the wind speed drops below the selected wind direction coasting threshold. The last calculated direction output remains until the wind speed increases enough to reach the threshold and
WMT700 returns to normal operation Vector Averaging
When you select vector averaging, WMT700 calculates wind speed and direction averages by adding up each x velocity and y velocity measurement from the averaging time and then dividing the sum by the number of measurements. WMT700 converts the resultant average x velocity and average y velocity to polar direction and magnitude, which returns the wind direction average in degrees and wind speed average in the chosen units.
If the data acquisition system requests data before the initial averaging time completes, the sensor returns the most recent complete measurement data.
Chapter 3 – Functional Description
37


3.4 Measurement Methods
WMT700 measures wind speed and direction either continuously or for the duration of the user-configurable averaging time. You can select the measurement mode over the serial interface Continuous Measurement
You can set WMT700 to measure wind data continuously and stop the measurement with the


Document code
Testsetup according to
More information
Optiontemperature range
Optionheating
Optionhardware interface
Optionunit used
Optionoutput configuration
Selectionoutput configuration
Optionadapter type
Optionaccessories
Order codedescription
Aout1 selected option
Output signal
Swnddiroffset,(angle)
Parameterdefinition
Power supplywire colors
Used heating option
Heating option
Wire type/cable length
Descriptionspare part item
Wmt700connector pin
Open commandto activate the command, press enter
Commanddescription
Wind_getfetches wind calibration information.more information
S command. power must be on for at least 5 seconds after the s
Startcommand.more information
Itemdescription
Bitdescription
G command to fetch the current wmt700 parameters. disable error messages with the command s messages,0
Errors. if all values are valid, wmt700 sends the following response:0,0,0,0you can also use the g
Data message number
Ws425 and sdi messages
Parametername
Parameterdefault
Start command.to stop measurement, use the stop
Wb,wfirmware
Wf output:wff6785672109876.5432.1k99xx5.21.2 ws425 f/g asos data messagewmt700 responds to the wa
Bytedescription
Parameterdefault value
Id character
Wx command with a character fixed-length data message.character
Start command. to stop measurement, use thestop
Problemprobable cause
Error/eventcode
Parameter name
Propertydescription/value
Analog outputs for wind direction
Itemorder code
Configuration mode / measurement
Settingparameter
Start command. you can stop the measurement with the stop
Example of the command and response:
Baud........................................................................ 105clearerr
S............................................................................... 103sleep
Gget message. get parameter.........................................................104h
Jjunction box...............................................................28l



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