ASTM_D_4480_-_93_scan.pdf

ASTM D4480 93 m Oi5=l530 0524239 35T m Designation:D 4480-93 AMERICAN SOCIETY MR TESTING AND MATERIALS 1916 Race St.Philadelphia,Pa 19103 Reprinted from the Annual&ok of ASTM Standards.CopyrigM ASTM If not listed in the current combined index.will appear in the neti edKin Standard Test Method for Measuring Surface Wind by Means of Wind Vanes and Rotating Anemometers This standard is issued under the fixed designation D 4480;the number immediately following the designation indicates the year of original adoption or,in the tax of revision,the year of last revision.A number in parentheses indicates the year of last reapprowl.A superscript epsilon(0 indicates an editorial change since the last revision or reapproval.1.Scope 1.1 This test method describes the measurement of hori-zontal wind velocity by means of commercially available rotating anemometers and wind vanes attached to the earths surface in the ambient atmosphere.Wind speeds can be measured in the range of 0.2 to 100 m/s using such anemometers.All wind directions may be measured by commercially available wind vanes within the operating speed range.1.2 This standard does not purport to address all of the safety problems,if any,associated with its use.It is the responsibility of the user of this standard to consult and establish appropriate safety and health practices and deter-mine the applicability of regulatory limitations prior to use.2.Referenced Document 2.1 ASTM Standard:D 5096 Test Method for Determining the Performance of a Cup Anemometer or Propeller Anemometes 3.Terminology 3.1 Definitions:3.1.1 damped natural frequency(Hz)-the frequency at which a damped second-order sensor(or recorder,etc.)oscillates after being disturbed.3.1.2 damped natural periods-the period required by a damped second-order sensor to undergo one complete oscil-lation;also the reciprocal of damped natural frequency.3.1.3 damped natural wavelength-the product of the speed of the wind past a wind vane and the damped natural period of the wind vane.At sea level in the U.S.standard atmosphere,damped natural wavelength is related to delay distance,D,and damping ratio by the approximate expres-sion:xd=06.0-2.41 Jc7(1)3.1.4 damping ratio-the ratio of the actual damping coefficient to the critical damping coeffkient.The damping ratio t is determined by:This teat method is under the jurisdiction of ASTM Committee D-22 on Sampling and Analysis of Atmospheres and is the direct responsibility of Subcommittee D22.1 I on Meteorology.Current edition approved Feb.15,1993.Published April 1993.Originally published as D 4480-85.Last previous edition D 4480-85.2 Annual Book of ASTM Slcmdards,Vol 11.03.(2)where Sz,the overshoot ratio,is readily measurable.3.1.5 delay distance-the distance the air flowing past a wind vane moves while the wind vane is responding to 50%of a step change in wind direction.3.1.6 distance constant(m)-the distance the air flowing past an anemometer moves while the anemometer is re-sponding to 63.2%of a step increase or decrease in wind speed.This is determined by anemometer characteristics and fluid density and is not a function of wind speed.3.1.7 first-order sensor-a sensor for which the equation of forces on the sensor is a first-order differential equation.Such sensors,if suddenly subjected to a step change in the variable they are measuring,will approach the new value asymtotically at a rate which is directly proportional to the difference between the new equilibrium value and the value being registered by the sensor.A first-order sensor does not overshoot the new equilibrium value.3.1.8 overshoot ratio-the ratio of the amplitudes of two successive deflections of a second-order sensor as it oscillates about the equilibrium position.Because all deflections after the first to the side opposite the release point are small,the initial release point(that is,the n=zero deflection)and the first deflection after release are used in practice in deter-mining overshoot ratio.When using this equation to calcu-late Sl for a wind vane,0,should not exceed lo.Overshoot ratio by a wind vane is expressed by the equation:where 8,and 8(,+,)are the amplitudes of the n and(n+1)deflections,respectively.3.1.9 second-order sensor-a sensor for which the equa-tion of forces on the sensor is a second-order differential equation.A second-order sensor will respond to a step change in the variable it is measuring by overshooting and then undergoing a damped harmonic oscillation about the new equilibrium position unless it is overdamped or criti-cally damped.If it is overdamped or critically damped,it will approach the new equilibrium position asymptotically.3.1.10 sensor-that part of an instrument which responds to the variable being measured.3.1.11 starting threshold(m/s)-the wind speed at which an anemometer or vane fast starts to perform within its specifications.3.1.12 synoptic-in meteorology,the meteorological data observed simultaneously over a wide area for the purpose of 1 NOTICE:Th