Instruction manual

1
CSAT3 THREE DIMENSIONAL SONIC ANEMOMETER
1. GENERAL
The CSAT3 is a three dimensional sonic
anemometer. It measures wind speed and the
speed of sound on three nonorthogonal axes.
From these measurements, orthogonal wind
speed and sonic temperature is computed.
The CSAT3 can be used to measure average
horizontal wind speed and direction or the
turbulent fluctuations of horizontal and vertical
wind. From the turbulent wind fluctuations,
momentum flux is calculated. By finding the
covariance between the vertical wind speed
fluctuations, and temperature and humidity
fluctuations (measured by fast response
sensors) the sensible and latent heat flux can
also be measured.
The sonic transducers are sealed and will not
be damaged should they become wet. The
wind measurements, however, will not be valid
because the water droplets, on the face of the
transducer, will scatter the sonic signal. As
soon as all the transducer faces dry, the CSAT3
will lock on to the wind signal and begin making
measurements.
The CSAT3 can be measured using SDM
(Synchronous Device for Measurements)
communications and a CSI datalogger. The
CR23X and CR10X can be used to measure
the CSAT3 using SDM without any special
operating system. A 21X requires CSAT3
PROMs (P/N 10006). The CSAT PROMs
includes the SDM-CSAT3 (P107), SDM Group
Trigger (P110), and Set SDM Clock (P108)
instructions. Initiate Telecommunications (P97)
has been removed from the PROMs. The
CR10 requires library special PROMs with the
following instructions: SDM-CSAT3 (P107),
SDM Group Trigger (P110), Set SDM Clock
(P115), and Covariance/Correlation (P62).
The fine wire thermocouple used with the
CSAT3 is the FW05. It is a 0.0005” diameter
thermocouple mounted on a stainless steel
bayonet. A FWC-L35 is required with the
FW05. Four feet of the FWC-L35 is bundled up
inside the enclosure to minimize conduction of
heat into the terminal strips. The remaining 31
feet permits mounting the FW05 to the side of
the CSAT3 head. Finally, the thermocouple
cover (P/N 10080) is placed over the
connectors. This cover is used to mount the
connectors to the side of the CSAT3 head and
minimized temperature gradient across the
omega brand connectors.
2. SPECIFICATIONS
MEASUREMENTS
The CSAT3 measures wind speed and the
speed of sound along the three nonorthogonal
sonic axes. The wind speeds are then
transformed into the orthogonal wind
components u
x
, u
y
, and u
z
and are referenced to
the anemometer head; the speed of sound, c,
or sonic virtual temperature, T
s
, is the average
between the three nonorthogonal sonic axes.
The errors caused by wind blowing normal to
the sonic path is corrected on-line, before the
wind speed is transformed into orthogonal
coordinates. The CSAT3 can be configured to
make a single measurement per trigger or
multiple measurements that are centered
around the trigger (oversampled).
MEASUREMENT RATE: programmable from 1
to 60 Hz.
NOISE EQUIVALENT WIND: u
x
and u
y
is
1 mm s
-1
; u
z
is 0.5 mm s
-1
; c is 1 mm s
-1
(0.002°C). Values are the standard deviations
of instantaneous measurements made of a
constant signal. The noise is unaffected by the
sample rate.
WIND MEASUREMENT OFFSET: less than ±4
cm s
-1
over -30° to 50°C operating range.
OUTPUT SIGNALS
The CSAT3 can output data to a data retrieval
system using any of the following
communications: SDM (Synchronous Device
for Measurement), RS-232, or analog output.
All the output signals have a two scan delay.
DIGITAL SDM: A CSI serial interface for
datalogger/sensor communication
Baud rate: 33.3 K (maximum)
Data type: 2-byte integer