The air density (ρ) shall be calculated according to the following formula: This typically takes 1 minute, but it varies from facility to facility. Before taking readings at each wind speed, adequate time has to be allowed in order to establish stable flow conditions. The sampling frequency shall be at least 1 Hz and the sampling interval at least 30 s.
By measuring both increasing and decreasing steps, it is possible to identify whether hysteresis effects are present in the measuring equipment. Calibration Procedureīefore the calibration procedure begins, the anemometer shall run for about 5 minutes in order to avoid the fact that large temperature variations may influence the mechanical friction of the anemometer bearings.Ĭalibration shall be performed under both rising and falling wind speed in the range of 4 m/s to 16 m/s with steps of 1 m/s or less. The anemometer shall be positioned at the test section perpendicularly to the flow field of the wind tunnel as accurate as possible. The pitot tubes shall be positioned at the test section perpendicularly to the flow field of the wind tunnel as accurate as possible. It is important to ensure that the anemometer is not influenced by the presence of any reference wind speed measurement equipment. Mounting arrangements can have dramatic effects on instrument sensitivity, particularly if the ratio of tube diameter to rotor diameter is high.
#Anemometer calibration free#
This tube shall be of the same dimensions as the one on which the anemometer will be mounted in service in the free atmosphere. The maximum difference between these calibrations should be less that 0.5% at 10 m/s wind speed.ĭuring calibration the anemometer shall be mounted on top of a tube in order to minimise flow distortion. In order to assure the repeatability of the facility, five calibrations of a reference anemometer shall be performed. The wind tunnel calibration factor, which gives the relation between the conditions at the reference measurement position and those at the anemometer position, shall be appraised using pitot tubes. pitot tubes, hot wires or Laser Doppler Velocimetry. Flow uniformity can be estimated using velocity sensing devices, i.e. The flow across the area covered by the anemometer shall be uniform. The presence of the anemometer shall not substantially affect the flow field in the wind tunnel. There are also special requirements for the wind tunnel.
#Anemometer calibration iso#
An assessment of measurement uncertainty shall be carried out in accordance with ISO guidelines.The repeatability of the calibration shall be verified.Prior to every calibration, the setup must be verified by means of comparative calibration of a reference anemometer.The pitot tubes used must be calibrated for appropriate wind speed ranges and be documented.Calibration certificates and reports shall contain all relevant traceability information. All transducers and measuring equipment shall have traceable calibrations.There are several requirements for anemometers’ calibration that must be taken into account: By measuring the difference between these pressures, the dynamic pressure can be obtained according to Bernoulli’s formula, which can be used to calculate airspeed. The side hole measures the static pressure.
The front hole is placed directly into the fluid flow and it measures the stagnation pressure. The pilot tube is a slim tube which has two holes on it. Pitot tubes: They are pressure measuring instruments used to measure fluid flow velocity.The instrument under test is placed in the middle of the tunnel and it is fastened so it does not move.
The fan must have straightening vanes to smooth the airflow. They have a fan which moves the air inside.
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