Campbell Scientific CPEC200 Closed-Path Eddy-Covariance System - Manual (Page 24)

CPEC200 Closed-Path Eddy-Covariance System
4.2.2 CSAT3A Sonic Anemometer Head
The CSAT3A, as shown in FIGURE 4-17, is an ultrasonic anemometer sensor
head for measuring wind speed in three dimensions. It shares integrated
electronics, the EC100 electronics, with the EC155 gas analyzer. It is similar
to the sensor head for the CSAT3 sonic anemometer, with the primary
difference being that the CSAT3 can be used as a standalone anemometer
because it includes independent electronics. The CSAT3A uses three
nonorthogonal pairs of transducers to sense the wind velocity vector. Each pair
of transducers transmits and receives ultrasonic pulses to determine the time of
flight, which is directly related to the speed of sound and the wind speed along
the line between the pair of transducers. The CSAT3A transforms the results
into orthogonal wind components u
x
, u
y
, and u
z
, referenced to the anemometer
head.
The CSAT3A also determines the speed of sound for each transducer pair.
These measurements are averaged and converted to sonic virtual temperature
(T
s
) based on the relationship between speed of sound and air temperature. For
more detailed information and specifications, see the CSAT3 manual.
FIGURE 4-17. CSAT3A sonic anemometer head
4.2.3 Valve Module
The optional valve module, shown in FIGURE 4-8, is housed in the CPEC200
enclosure and is used to automate zero and CO
2
span checks, and automatically
perform a zero and CO
2
span on a user-defined interval. As described in
Section 4.1.2.3, CPEC200 Valve Module, H
2
O span requires a dewpoint
generator and cannot be automated.
The CPEC200 valve module is available in two versions, one with three valves
(pn 27559) and another with six valves (pn 26578). The valve module is
normally ordered as a factory-installed option, but can also be ordered
separately and installed by the user.
14