CTA Calibration Systems

image of StreamLine Pro Automatic Calibrator
StreamLine® Pro Automatic Calibrator

StreamLine® Pro Automatic Calibrator

The StreamLine Pro Automatic Calibrator facilitates fast and accurate calibrations of probes over a large velocity range (0.02 m/s to > 300m/s) in direct connection with experiments. Clean and dry air from a pressurised air supply must be supplied for the operation. By connecting the calibrator via USB or Ethernet to a computer running the supporting software, StreamWare Pro, the system is ready to use.

The compact design makes it possible to perform in situ calibrations of probes in fixed locations such as wind tunnels. Relying on an aerodynamically designed flow section, high-precision transducers, and control valves, the calibrator generates a free low-turbulence jet that is used as a velocity reference for calibrations. The probe to be calibrated is placed at the jet exit. The unit can be equipped with a pitch-yaw manipulator that allows 2D and 3D probes to be rotated for calibration of directional sensitivity for manual directional calibration, or with the Automatic Directional Calibrator.

StreamLine® Pro Automatic Directional Calibrator

Multiple-sensor hotwire probes require directional calibration for accurate flow measurements.

The directional calibration was previously performed using a manual directional calibrator where the probe orientation is changed with respect to a known flow. This was a time-consuming task, and the accuracy and repeatability of the angular settings was user dependent.

Directional calibration of multiple-sensor hotwire or hotfilm probes can now be fully automated using the Automatic Directional Calibrator. Controlled by the StreamWare Pro software, it inclines the probe in relation to the flow and rotates it through 360°. The automation makes this task faster, user-friendly, accurate, and precise.

The directional calibrator is mounted on top of the StreamLine Pro Automatic Calibrator. The motorisation feature speeds up directional calibrations and makes them more accurate than those achieved with manual calibration. It facilitates mapping of how the pitch and yaw factors are influenced by velocity and angles.

The benefit of the Automatic Directional Calibrator is seen when the true error during the calibration is considered. Below are two plots displaying the amount of true error using two sets of pitch and yaw coefficients. The first one is using the library default values (left) when a directional calibrator is absent from the measurement system and the second one is using the calculated values (right) using an Automatic Directional Calibrator.

image of pitch and yaw coefficients
Left: library default values for pitch and yaw coefficients gives errors up to 1 m/s Right: calculated values based on directional calibration gives errors below 0.2 m/s

The benefits are three-fold:

  • The absolute velocity error is reduced up to 10x using a directional calibrator
  • The procedure is completely automated so the user does not have to focus on the rigorous calibration procedure, but rather on the experiment
  • The angles are set quickly and accurately which saves valuable time during a directional calibration

Hot-wire Calibrator

The Dantec Dynamics Hot-Wire Calibrator is a simple and accurate device for 2-point calibration of most hot-wire probes used with Constant Temperature Anemometers. The calibrator produces a free jet, where the probe is placed during calibration. It requires a normal pressurized air supply and is able to set velocities from 0.5 m/s to 60 m/s.

It is primarily designed to provide two-point calibrations of standard wire probes, but can also be used for multi-point calibrations. By combining two sets of measured velocity-voltage values with a generic uni-curve transfer function, it is possible to create a calibration function for an actual probe which is valid for the entire velocity range.

image of hot wire calibrator
Hot-wire Calibrator

Water calibrator for CTA film probes

Even if CTA has been replaced by LDA and PIV in many water applications, the use of film probes may still be an attractive option in special cases. Dantec Dynamics offers a calibrator for this purpose.

The calibrator is a recirculating water tunnel with a submerged jet in a water reservoir in front of the jet. It covers velocities from 0.005 to 2 m/s with combinations of three different nozzles (600, 120 and 60 mm²). Velocity is calculated on the basis of a precision-variable area flowmeter reading. The calculation is made using an Excel spreadsheet supplied with the system.

More Information

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