Campbell CR1000 User Manual

Section 7. Installation
or, in the case of orthogonal sensors:
Resultant mean wind direction, Θu:
Standard deviation of wind direction, σ (Θu), using Campbell Scientific
algorithm:
The algorithm for σ (Θu) is developed by noting, as shown in the figure Standard
Deviation of Direction
(p. 300), that
where
Standard Deviation of Direction
Figure 78. Standard Deviation of Direction
The Taylor Series for the Cosine function, truncated after 2 terms is:
For deviations less than 40 degrees, the error in this approximation is less than
1%. At deviations of 60 degrees, the error is 10%.
The speed sample can be expressed as the deviation about the mean speed,
Equating the two expressions for Cos (θ') and using the previous equation for s
i
;
Solving for (Θ
i
')
2
, one obtains;
300

Campbell CR1000 Specifications

General

Power Requirements	9.6 to 16 VDC
Data Logger Operating System	CRBasic
Memory	4 MB
Analog Inputs	16 single-ended or 8 differential
Analog Input Resolution	13 bits
Analog Input Range	+/-2.5V
Digital I/O	8
Pulse Counters	2
Communication Ports	RS-232
Operating Temperature	-25°C to +50°C
Pulse Channels	4