Campbell Scientific CSAT3 3-D Sonic Anemometer - Manual (Page 49)

CSAT3 Three Dimensional Sonic Anemometer
FIGURE 11-2. P/N 28902 CSAT3 Sonic Wick Spares Kit contents
11.2 Calibration
The CSAT3 is calibrated over the temperature range of –30 to +50 °C
(standard) or –40 to +40 °C (cold shifted). The CSAT3 may or may not make
measurements outside the calibration range. Any measurements taken outside
the calibration range will be suspect. The CSAT3 does not require any field
calibration.
The CSAT3 electronics box contains unique calibration
information for its respective sensor head. Do not
mismatch CSAT3 sensor heads and electronics. Doing
so will result in erroneous wind and speed of sound
measurements.
If the CSAT3 requires a calibration, it will develop a wind offset greater than
the specifications, or it will set diagnostic flags, under dry conditions with little
to no wind and with no obstruction in the ultrasonic paths. CSAT3s running
embedded code version 4 will develop the offset first and then possibly set
diagnostic flags under dry conditions. CSAT3s running embedded code
version 3 will set diagnostic flags before a wind offset develops.
11.2.1 Cold Shifted Calibration
A CSAT3 with a cold shifted calibration is calibrated over the temperature of
–40 to +40 °C. To improve the speed of sound reporting resolution, the
CSAT3 sends the speed of sound minus an offset to a datalogger via the SDM
interface or a PC via the RS-232 interface. The data acquisition system must
add the appropriate offset to determine the speed of sound. For the standard
temperature range the offset 340 m s –1 . This offset is added by the
CSAT3()/SDM-CSAT3 (P107) instruction Command/Option 90, 91, 98, and
99. For the cold shifted calibration range, the offset is 337 m s –1 .
WARNING
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