Airspeed Calibration Service

1 Page 1 AIRSPEED CALIBRATION SERVICE NIST Special Publication 250-79 T.T. Yeh and J. M. Hall Fluid Metrology Group Process Measurements Division Chemical Science and Technology Laboratory National Institute of Standards and Tech... Open at page → 2 Page 2 ii Certain commercial equipment, instruments, or materials are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute of Standards and... Open at page → 3 Page 3 iii Table of Contents Page Abstract...........................................................................................................................................1 1. Introduction ............................... Open at page → 4 Page 4 1 Abstract The National Institute of Standards and Technology (NIST) provides calibration services for airspeed instrumentation such as Pitot-static tubes, anemometers (ultrasonic, thermal or hot-wire, cup, and propeller... Open at page → 5 Page 5 2 2. Description of the Measurement Service Customers should consult the web address www.cstl.nist.gov/div836/Fluid Metrology Group to find the most current information regarding our calibration services, calibration fee... Open at page → 6 Page 6 3 Orders, D.) Shipping, Insurance, and Risk of Loss, E.) Turnaround Time, and F.) Customer Checklist. Chapter 3 gives special instructions for customers outside the United States. The web address www.cstl.nist.gov/div836... Open at page → 7 Page 7 4 a transverse velocity gradient less than 1 % within a "working window" of 90 % of the test- section areas. Figure 1 NIST Wind Tunnel for Airspeed Calibration Service. To provide the light scattering particles necessary... Open at page → 8 Page 8 5 Figure 2 Photo of fine water droplets with the air-water spray nozzles 5. Primary Airspeed Standard -- LDA The primary standard for airspeed measurement at NIST is a fiber optic LDA. This instrument has been characteri... Open at page → 9 Page 9 6 interference pattern that is composed of parallel light and dark fringes. Small particles, entrained in, and moving at the same speed as the air stream, scatter light as they pass through each bright fringe in the inte... Open at page → 10 Page 10 7 Figure 3 Laser Beams and Their Intersection Angle for 1D Component. Table 1 Nominal Optical Parameters of the LDA Probe Laser wavelength λ, nm 514.5 Laser beam separation h, mm 72.5 Focal length f L, mm 1200 Beam inter... Open at page → 11 Page 11 8 calibrated at specified uncertainty levels. The value of d can be calculated from the laser wavelength λ and the beam angle θ if both θ and λ are calibrated. However, the calibration of the measured Doppler frequency... Open at page → 12 Page 12 9 where C Df is the frequency measured by the LDA system when it is scattering from the disk moving at the velocity DiskV. The NIST standard speed thus becomes C D D DiskLDALDANIST f f f D VCV 2 == (6) Thus, the NIST LDA... Open at page → 13 Page 13 10 5.3 NIST LDA Airspeed Uncertainty Analysis Here we follow the guidelines for evaluating and expressing uncertainty provided in NIST TN 1297 [9], the ISO Guide [10], and elsewhere [11]. In general, if a measurement qua... Open at page → 14 Page 14 11 Au or Bu. Referring to Eqns.(6) and (10), the airspeed uncertainty depends on the uncertainties of the variables of the diameter of the rotating cylinder D , the rotating frequency fDisk , and the Doppler frequencies... Open at page → 15 Page 15 12 is made from aluminum and its linear thermal expansion is assumed to be 1.7x10 -5 /K. Referring to Eqns. (1) and (2), and the optical parameters of the probe given in Table 1, for a 5 K difference in temperature, the... Open at page → 16 Page 16 13 the wire location. The data show that the measured velocity is a linear function with the wire location within the sensing volume (-3 mm to +3 mm on the graph). Therefore, particles passing through different locations... Open at page → 17 Page 17 14 0.97 0.98 0.99 1.00 1.01 1.02 1.03 -4 -3 -2 -1 0 1 2 3 4 Wire Position, mm V Disk / V LDA [-] Figure 7 LDV Calibration Results vs Wire Position. 5.3.7 The burst spectrum analyzer Frequency, C Df or Df, is determined b... Open at page → 18 Page 18 15 5.3.6 and shown in Fig. 7. The uncertainty as a function of the calibrated speed is plotted in Fig. 8. Diamond symbols shown in Fig. 8 are the combined uncertainty of the disk-LDA calibration data. This uncertainty is... Open at page → 19 Page 19 16 The Type A uncertainty of the BSA affects both C Df and Df independently and thus the resulting speed uncertainty is 2 x 0.0013 m/s = 0.0018 m/s for the constant speed term and 2 x 0.207 % = 0.29 % for the constant pe... Open at page → 20 Page 20 17 Axis of the rotating disk. Ris the distance between the wire and the axis x y Light scattering wire Laser V DISK φ z x w y b RC rotation nis an unit vector normal to the bisecting plane, φis the angle between V DISK a... Open at page → 21 Page 21 18 Table 2 Summary of Sources and NIST Airspeed Uncertainties. Sources Speed Uncertainty Variable Sources Section Mean u A u B uA % uB % Diameter of rotating disk, D [mm] 5.3.1 136.5 0 0.005 0 0.0037 Thermal expansion of... Open at page → 22 Page 22 19 ( ) 22 )0018.0(0032.0)( += LDANIST VkVU (12) When a coverage factor of 2 =k is used to convert the combined standard uncertainty to an expanded uncertainty, with an approximate 95 % level of confidence, the expanded u... Open at page → 23 Page 23 20 0 1 2 3 0.1 1 10 100 Airspeed , m/s Airspeed Uncertainty, k=2, % Dashed line - Spinning disk Figure 11 NIST Airspeed Uncertainty in % versus Airspeed 5.4 Uncertainty of Airspeed Calibration The uncertainty analysis re... Open at page → 24 Page 24 21 and then returned to the same nominal value. To measure the reproducibility of the test, uR, the standard deviation of the air speed ratio at each of the nominal air speeds was used to calculate the relative standard... Open at page → 25 Page 25 22 Fig. 12 is a sketch of a typical version of the device. It is comprised of two concentric tubes. The center tube is open; the annular space between the tubes is sealed at one end. There is a band of small, radial hole... Open at page → 26 Page 26 23 The NIST pst system is calibrated periodically with the LDA system. The sample calibration data for the air speed ratio, Y = VNIST / Vpst , taken in a period of a year, are shown in Fig. 13. Without calibration, the t... Open at page → 27 Page 27 24 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 0 10 20 30 40 V pst (m/s) 100(V NIST /V pst -fit) Figure 14 Deviation of the speed ratio Y for the pst probe from the curve fit. Data taken between 4/12/05 and 2/1/06. 6.2. Ther... Open at page → 28 Page 28 25 0.96 1.00 1.04 1.08 1.12 0 10 20 30 40 V Ta (m/s) V LDA / V Ta Figure 15 NIST Ta airspeed vs. NIST Standard airspeed. Data taken between 4/12/05 and 4/5/06. Solid line is a curve fit. -4 -2 0 2 4 0 10 20 30 40 V Ta (m... Open at page → 29 Page 29 26 References [1] NIST Calibration Service Users Guide 1998, J.L. Marshall, Editor, NIST Special Publication 250, January 1998, National Institute of Standards and Technology, Gaithersburg, MD. [2] Mease, N.E., Cleveland... Open at page → 30 Page 30 1 Appendix A: Sample Calibration Report REPORT OF CALIBRATION FOR AIR SPEED INSTRUMENTATION May 01, 2007 Shortridge Model ADM 870C Airdata Multimeter Serial Number M03327 with Airflow Technical Products Pitot-Static Tube... Open at page → 31 Page 31 NIST Test No.: 836-123456-07 Service ID Number: 19020C Calibrated April 12-14, 2007 by Mike Hall and T. T. Yeh 2 of 34 uncertainty calculated as described below. Figure 1. Instrument under test in NIST Wind Tunnel, viewe... Open at page → 32 Page 32 NIST Test No.: 836-123456-07 Service ID Number: 19020C Calibrated April 12-14, 2007 by Mike Hall and T. T. Yeh 3 of 34 NISTV uis the standard uncertainty of the air speed measurements made with the LDA. The expanded unce... Open at page → 33 Page 33 NIST Test No.: 836-123456-07 Service ID Number: 19020C Calibrated April 12-14, 2007 by Mike Hall and T. T. Yeh 4 of 34 The quantity Acq u is the standard uncertainty of the data acquisition system and instrumentation use... Open at page → 34 Page 34 NIST Test No.: 836-123456-07 Service ID Number: 19020C Calibrated April 12-14, 2007 by Mike Hall and T. T. Yeh 5 of 34 For the Director, National Institute of Standards and Technology Fluid Metrology Group Process Measur... Open at page →