CSAT3

3-D Sonic Anemometer

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 can be computed.

The CSAT is used in eddy covariance applications to measure the turbulent fluctuations of horizontal and vertical wind. From the turbulent wind fluctuations, momentum flux and friction velocity can be calculated. The CSAT3 can also be used to measure average horizontal wind speed and direction.


Features

  • Measures turbulent fluctuations of horizontal and vertical wind
  • Measures wind speed and the speed of sound on three nonorthogonal axes.
  • Provides upper and lower transducers that are separated by a vertical distance of 10 cm and are oriented 60 degrees from horizontal.
  • Typically used with fine wire thermocouples and LI7500 (or KH20) in Eddy covariance systems
  • No moving parts

Specifications

Measurements

  • Outputs: ux, uy, uz, c (ux, uy, uz are wind components referenced to the anemometer axes; c is speed of sound)
  • Speed of Sound: Determined from three acoustic paths; corrected for crosswind effects
  • Measurement Rate: programmable from 1 to 60 Hz, instantaneous measurements; two over-sampled modes are block averaged to either 20 Hz or 10 Hz
  • Measurement Resolution: ux, uy is 1 mm/s rms; uz is 0.5 mm/s rms; c is 15 mm/s (0.025°C) rms; values are for instantaneous measurements made on a constant signal; noise is not affected by sample rate
  • Accuracy (assumes -30° to +50°C range; wind speeds <30 m/s; wind angles between ±170°)
    • Offset Error: <±4.0 cm/s (ux, uy); <±2.0 cm/s (uz)
    • Gain Error: <±2% of reading (wind vector within ±5° of horizontal); <±3% of reading (wind vector within ±10° of horizontal); <±6% of reading (wind vector within ±20° of horizontal)
  • Rain: Innovative ultrasonic signal processing and user-installable wicks considerably improve the performance of the anemometer under all rain events

Output Signals

  • Digital SDM: CSI 33.3 k baud serial interface
    for datalogger/sensor communication. Data type is 2-byte integer per output plus 2-byte diagnostic
  • Digital RS-232
    • Baud Rate: 9600, 19200 bps
    • Data Type: 2-byte integer per output plus 2-byte diagnostic
  • Analog
    • Number of Outputs: 4
    • Voltage Range: ±5 V
    • Number of Bits: 12

Reporting Range

  • SDM and RS-232 Digital Outputs
    • Full Scale Wind: ±65.535 m/s autoranging between four ranges; least significant bit is 0.25 to 2 mm/s
    • Speed of Sound: 300 to 366 m/s (-50° to +60°C); least significant bit is 1 mm/s (0.002°C)
  • Analog Outputs: see chart in product brochure