approximately the area covered by the cup anemometer rotating cups. A set of measurements shall be made and the linear regression between the dynamic pressures measured by the two pitot tubes shall be calculated. The difference shall be less than 0.2%. The axial turbulence intensity at the anemometer's position shall be below 2%. turbulence intensity. Check for details of two pitot tubes used for the purpose and verification that they are identical 13 page 58, paragraph 6, line 1 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. Check for the details of assessment of wind tunnel calibration factor. 14 page 59, paragraph 1, line 1 The facility shall undergo a detailed examination of the repeatability of anemometer calibration. The facility shall designate a reference anemometer for use in these tests. The reference anemometer shall be used only for checking performance of this and other anemometer facilities. Check for all the details required to repeat the anemometer calibration Check for details of the designated reference anemometer for the facility 15 page 59, paragraph 1, line 4 The repeatability examination shall include at least 5 calibrations of the reference anemometers (over various atmospheric conditions). The maximum difference between calibrations should be less than 0.5% at 10 m/s wind speed. The process shall be repeated after any modification or recalibration of the facility. Check for details from 5 calibrations performed on reference anemometer during repeatability examination. Check for the measure of difference between 5 calibrations Check for details of any modifications or recalibration of the test facility. 16 page 59, paragraph 2, line 1 The facility shall prove, through round robin testing, that its results are comparable with other anemometer calibration facilities. Check for details of round robin tests. Clause F.3: Instrumentation and calibration set-up requirements.
17 page 59, paragraph 3, line 1 Dedicated external signal conditioning equipment such as frequency to voltage converters, etc. shall be calibrated in isolation from the anemometer, so allowing the anemometer's calibration to be derived and reported in isolation from signal conditioning equipment. Check for details of the signal conditioning equipment used in the test facility. Check for the calibration reports of the entire listed signal conditioning equipment. 18 page 59, paragraph 4, line 1 The resolution of the data acquisition system shall be at least 0.02 m/s. Care shall also be exercised in the case of an analogue voltage instrument, to ensure that the signal is adequately buffered to prevent its attenuation by low impedance logging equipment. Check for details of the data acquisition system Check for the resolution used in the data acquisition system 19 page 59, paragraph 5, line 1 During calibration the anemometer shall be mounted on top of a tube in order to minimize flow distortion. This tube shall be of the same dimensions as the one on which the anemometer will be mounted in service in the free atmosphere. Check for details of mounting specifications during the anemometer calibration. Check for details of mounting specifications required during service. 20 page 59, paragraph 6, line 1 It is important to ensure that the anemometer is not influenced by the presence of any reference wind speed measurement equipment. Conversely, the presence of anemometer shall not affect the flow in the region of the reference instrument. If flow distortion effects are encountered, then the pitot tube shall be repositioned. Check for details of position of anemometer and reference wind speed measurement equipment in the wind tunnel. Check for details of assessment of flow distortion from instruments on each other. 21 page 59, paragraph 7, line 1 The pitot tubes shall be positioned at the test section perpendicular to the flow field of the wind tunnel as accurate as possible. Check for positioning of pitot tube with respect to flow field. 22 page 59, paragraph 8, line 1 The anemometer shall be positioned at the test section perpendicular to the flow field of the wind tunnel as accurate as possible. Check for positioning of anemometer with respect to flow field.
23 page 59, paragraph 9, line 1 During calibration, the anemometer output signal be examined to ensure that it is not subjected to interference or noise. Check for quality assessment of the anemometer output signal. Clause F.4: Calibration procedure 24 page 59, paragraph 10, line 1 The anemometer shall run in for about 5 min before the calibration procedure begins in order to avoid the effect that large temperature variations may have on the mechanical frication of the anemometer bearings. Calibration shall be performed under both rising and falling wind speed in the range of 4 m/s to 16 m/s at a calibration interval of 1 m/s or less. Check for details of operational procedures followed during the anemometer calibration (test log) Check for the range of wind speed in which the calibration was performed and the calibration interval within the defined range. 25 page 60, paragraph1, line 1 The sampling frequency shall be 1 Hz and the sampling interval at least 30 s. This time shall be increased when low resolution anemometers are calibrated. Check for details of the sampling frequency and sampling interval. Check for resolution details of the anemometer which will be calibrated. 26 page 60, paragraph1, line 4 Before collecting data at each wind speed, adequate time shall be allowed for stable flow conditions to become established. Check for details of operational procedures followed during the anemometer calibration (test log) 27 page 60, paragraph 2, line 1 Air density ρ shall be calculated on the basis of the mean wind tunnel air temperature T, relative humidity φ and barometric pressure B using equation (F.1). Check for records of measured air temperature, pressure and relative humidity. Check for estimation of air density at the time of calibration. 28 page 60, paragraph 4, line 2 If no blockage correction factor is calculated, then about 1/4 of the blockage ratio shall be used for the uncertainty calculation for closed for details of estimation of blockage correction factor.
wind tunnels and 1/16 for open wind tunnel. Check for details of estimation of blockage ratio. Check for the details of wind tunnel type being used for anemometer calibration Clause F.5: Data analysis 29 page 61, paragraph 1, line 1 A linear regression analysis shall be carried out on the calibration data for the estimation of the following regression parameters: offset, slope, regression coefficient, standard uncertainty in the slope and intercept and covariance of the slope and intercept of the wind speed. The wind speed values shall be regressed upon the anemometer outputs. Check for the details of linear regression carried on the calibration data. 30 page 61, paragraph 2, line 1 If the correlation coefficient, r, for the data is less than 0.99995 then the calibration shall be repeated. If coefficient is still insufficiently high, then either the calibration facility is inadequate or the anemometer is excessively non-linear and shall not be used. Check for estimation of correlation coefficient r, for the calibrated data. Clause F.6: Uncertainty analysis 31 page 61, paragraph 3, line 4 The magnitude of the net uncertainty shall be assessed statistically and shall take account of: - flow speed measurement uncertainty - frequency measurements - wind tunnel calibration including blockage effect - flow variability in the vicinity of the anemometer. Check for the assessment of uncertainty in the calibrated data. Check against the list of uncertainties in the estimation. Clause F.7: Reporting format 32 page 61, paragraph 4, line 1 The relevant documentation shall provide information on the procedure followed and the facility used for calibrating the anemometers (test report on the calibration campaign) and on the individual anemometer calibration (anemometer calibration report). Check for all the documentations necessary to understand the anemometer calibration process. Check for the details of all the procedures