CSAT3A 3-D Sonic Anemometer, Head Only
Precision Measurements
Best instrument for flux and other high-level turbulence research projects
weather applications water applications energy applications gas flux and turbulence applications infrastructure applications soil applications

Overview

The CSAT3A sonic anemometer head is similar to the sensor head from the CSAT3 sonic anemometer, but its cable is modified to connect to the EC100 electronics. It is used as part of the EC150 open-path analyzer and the CPEC200 closed-path eddy-covariance system.


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Benefits and Features

  • New conformal coating helps protect sonic transducers in corrosive environments
  • Innovative design provides precision turbulence measurements with minimal flow distortion
  • Usually combined with EC150 or EC155 gas analyzers giving near complete colocation for eddy-covariance measurements
  • Compatible with most Campbell Scientific data loggers
  • Measurements can be used to calculate momentum flux and friction velocity
  • Campbell Scientific’s fine wire thermocouples are an option for fast-response temperature measurements
  • Field rugged
  • Innovative signal processing and transducer wicks considerably improve performance of the anemometer during rain events
  • Sealed sonic transducers and electronics

Images

CSAT3A lower transducer assembly top view

Detailed Description

The CSAT3A is an optional component of an EC150 open-path or EC155 closed-path CO2/H2O gas analyzer. It attaches to a common mounting bracket and connects to the gas analyzer's EC100 electronics module.

Specifications

Measurement Path Length
  • 10.0 cm (3.94 in.) vertical
  • 5.8 cm (2.3 in.) horizontal
Path Angle from Horizontal 60°
Construction Sealed sonic transducers and electronics
Anemometer Head Materials Stainless-steel tubing
Electronics Box Materials Welded aluminum
Operating Temperature Range -30° to +50°C
Voltage Supply 10 to 16 Vdc
Current
  • 200 mA (60 Hz measurement rate)
  • 100 mA (20 Hz measurement rate)
Digital SDM Output Signal CSI 33.3 k baud serial interface for datalogger/sensor communication. (Data type is 2-byte integer per output plus 2-byte diagnostic.)
Support Arm Diameter 1.59 cm (0.63 in.)
Transducer Diameter 0.64 cm (0.25 in.)
Transducer Mounting Arm Diameter 0.84 cm (0.33 in.)
Anemometer Head Dimensions 47.3 x 42.4 cm (18.6 x 16.7 in.)
Anemometer Head Weight 1.7 kg (3.7 lb)

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.
Output Bandwidths 5, 10, 12.5, or 20 Hz
Output Rate 10, 20, 25, or 50 Hz
Measurement Resolution
  • Resolution values are for instantaneous measurements made on a constant signal; noise is not affected by sample rate.
  • 1 mm/s rms (ux, uy)
  • 0.5 mm/s rms (uz)
  • 15 mm/s (0.025°C) rms (c)
Offset Error
  • Offset error and gain error values assume the -30° to +50°C range, wind speeds of < 30 m/s, and wind angles between ±170°.
  • < ±8.0 cm/s (ux, uy)
  • < ±4.0 cm/s (uz)
Gain Error
  • Offset error and gain error values assume the -30° to +50°C range, wind speeds of < 30 m/s, and wind angles between ±170°.
  • < ±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.

Digital USB and RS-485 Output Signal
Baud Rate 230400 bps (maximum)
Data Type Comma-delimited ASCII

SDM, USB, & RS-485 Digital Outputs Reporting Range
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).

Compatibility

Please note: The following shows notable compatibility information. It is not a comprehensive list of all compatible products.

Dataloggers

Product Compatible Note
CR1000 (retired)
CR200X (retired)
CR211X (retired)
CR216X (retired)
CR3000 (retired)
CR5000 (retired)
CR800 (retired)
CR850 (retired)
CR9000X (retired)

Frequently Asked Questions

Number of FAQs related to CSAT3A: 22

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  1. Can the CSAT3/3A/3AH give a time stamp with each measurement value?

    No. The CSAT3/3A/3AH is a sensor. Time stamps are assigned to the sonic anemometer data by the data-acquisition system—typically a Campbell Scientific data logger or PC.

  2. Can a CSAT3A, CSAT3AH, CSAT3B, or CSAT3BH be used to measure wind flow angle, horizontal angle, and wind speed for the purpose of power curve testing?

    The sonic anemometer measures three-dimensional wind in a right-handed Cartesian coordinate system. From these measurements, use trigonometry to compute the wind flow angle, horizontal angle, and wind speed.

  3. Is there a way to determine the time at which the CSAT3A, CSAT3AH, CSAT3B, or CSAT3BH started reporting data with sub-second precision?

    No. The sonic anemometer does not report time with the wind measurements. A time stamp will be assigned to the wind data by the data-acquisition system—either a data logger or a PC.

  4. Are there any mounting options for the CSAT3A, CSAT3AH, CSAT3B, or CSAT3BH that lend themselves to frequent repositioning?

    Campbell Scientific does not offer any mounting booms or hardware that enable easy and frequent positioning of the sonic anemometer sensor head. This type of hardware must be provided by the user.

  5. What is the absolute accuracy of the speed of sound measurement in the CSAT3/3A/3AH?

    The CSAT3/3A/3AH should not be used to measure absolute sonic temperature. Aside from the effects of water vapor in the sonic path, the speed of sound measurement is highly dependent on the ability of the sonic anemometer to maintain its geometry. A 0.2 mm change in the sonic path is equal to a 1°C change in the measured absolute sonic temperature at 25°C. This is equal to a 0.33% error in the absolute sonic temperature. The wind speed measurements are also dependent on the sonic path distance, but to a lesser degree.

  6. How is sensible heat flux measured using a CSAT3/3A/3H and an FW05?

    Sensible heat flux is defined as the covariance of vertical wind and temperature fluctuations, measured with fast-response sensors. For more information, refer to a micrometeorology textbook.

  7. What are the calibration procedures for the CSAT3A, CSAT3AH, CSAT3B, and CSAT3BH, and how are they traceable to the National Institute of Standards and Technology (NIST)?

    The CSAT3A, CSAT3AH, CSAT3B, and CSAT3BH are calibrated over temperature for the effects of transducer delays on the wind speed, and to a lesser extent, for the speed of sound measurements.

    There is no NIST-traceable standard for ultrasonic anemometers.

  8. Is the CSAT3A, CSAT3AH, CSAT3B, or CSAT3BH anemometer measurement limited by precipitation?

    Ultrasonic anemometers are unable to make measurements if the sonic path is blocked. The path may become blocked by water that puddles on the lower transducer face or droplets that hang from the upper transducers. Sonic wicks, which come with all sonics, can be placed on the transducers to wick away moisture from the faces of the transducers. Ensure that these wicks are removed during cold conditions to prevent ice from building up around them.

  9. If the temperature drops below -30°C, is that a problem for a CSAT3A or CSAT3B?

    The CSAT3A or CSAT3B is calibrated over the temperature range of -30° to +50°C. The sonic anemometer operating temperature range can be shifted by 10 degrees to cover the range of -40° to +40°C. For low-temperature applications, it may be more appropriate to consider a heated version of our sonic anemometers.

    The instrument will continue to operate outside the calibrated temperature range until the signal becomes too weak; however, the proper calibration will not be applied to the measurements because the calibration file only spans the specified temperature range.

  10. Is the crosswind correction applied to the raw data of the CSAT3A, CSAT3AH, CSAT3B, or CSAT3BH?

    Yes. The effect of wind blowing normal to the sonic path on the speed of sound (sonic temperature) is corrected for in the electronics of the sonic anemometer. The corrections to the speed of sound (sonic temperature) described in

    Liu, H., Peters, G., and Foken, T.:  2001, “New Equations for Sonic Temperature Variance and Buoyancy Heat Flux with an Omnidirectional Sonic Anemometer,” Boundary-Layer Meteorol., 100, 459-468.
     
    Schotanus, P., Nieuwstadt, F. T. M., and de Bruin, H. A. R.:  1983, “Temperature Measurement with a Sonic Anemometer and its Application to Heat and Moisture Fluxes,” Boundary-Layer Meteorol., 26, 81-93.

    need not be applied to the sonic anemometer speed of sound (sonic temperature) data.

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