GHM DeltaOHM HD51.3D Series, Operating Manual

Page: 27 / 42

HD51.3D…
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V2.0
Command Reply Description
cor n cor| Sets the measurement rate to n Hz (meas-
urements per second)
Value should range within 1 and 4
Default : 4
ror n samples per second Reads the measurement rate set in the in-
strument
N
OTE
3 : W
IND SPEED THRESHOLD VALUE
If the wind speed is very low, the determination of the direction can result inaccurate. The in-
strument allows setting the threshold value of speed below which the direction value is frozen
on the last acquired value.
N
OTE
4 : S
CALAR AVERAGE AND VECTOR AVERAGE
Scalar average : the average intensity is calculated as average of intensities. For the calcula-
tion of the average direction, also called “prevailing direction”, the velocity versor (unit vector
having the same direction of the velocity vector) is considered for each measurement, and the
versor coordinates along the measurement axes are calculated, then the average of the coordi-
nates along each axis is calculated. The two average coordinates determine the average versor
and therefore the average direction. The average direction is expressed according to the ex-
tended characteristic for the analog output (see
Note 5 ).
Vector average : for each measurement, the coordinates of the velocity vector along the
measurement axes are calculated and then the average of the coordinates along each axis is
calculated. The average intensity and the average direction are those determined by the two
average coordinates.
N
OTE
5 : W
IND DIRECTION EXTENDED CHARACTERISTIC
With 0÷359.9° wind direction measuring range, the analog output continues to oscillate be-
tween maximum and minimum scale if the direction continues to slightly fluctuate around 0°:
This effect can be reduced through the extended ("wrap-around") characteristic of wind direc-
tion. In this mode, the wind direction is considered as corresponding to 0÷539.9° range in-
stead of 0÷359.9°. The wide output fluctuation occurs the first time that the wind direction
goes from 0 to 359.9°; if later the “physical” direction goes back to 0°, the analog output will
always remain around 360°. Using the extended characteristic, the behavior of the above
graph changes into the following: