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IC 
 
 9003 
 
 
 Bureau of Mines Information Circular/1985 
 
 Effect of Turbulence on Vortex-Shedding 
 Air-Velocity Transducers 
 
 By A. F. Cohen 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
 CD 
 
 c 
 
 ID 
 
 m 
 > 
 
 c 
 
 75 
 
 'Wines 75th av^ 
 
Information Circular 9003 
 
 Effect of Turbulence on Vortex-Shedding 
 Air- Velocity Transducers 
 
 By A. F. Cohen 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 William P. Clark, Secretary 
 
 BUREAU OF MINES 
 Robert C. Horton, Director 
 
# 
 
 ofo 
 
 \N^. 
 
 AD' 
 
 Library of Congress Cataloging in Publication Data: 
 
 Cohen, A. F 4 
 
 Effect of turbulence on vortex-shedding air-velocity transducers. 
 
 (Information circular ; 9003) 
 
 Bibliography: p. 11. 
 
 Supt. of Docs, no.: I 28.27:9003. 
 
 1. Mine ventilation — Equipment and supplies. 2. Air flow— Measure- 
 ment— Instrument. 3. Turbulence. 4. Coal mines and mining— Safety 
 measures. I. Title. II. Series: Information circular (United States. 
 Bureau of Mines) ; 9003. 
 
 TN295.U4 [TN301] 622s [622\8l 84-600145 
 
^T|) CONTENTS 
 
 -^Abstract 1 
 
 —^Introduction 1 
 
 -^Mi ne turbulence 2 
 
 ~ < ^Eurrent investigation 2 
 
 * Principle of operation 3 
 
 Wind tunnel and turbulence grid and T.I. characterization 3 
 
 CJ Calibration of BA4 and VA216B 5 
 
 BA4 experiments 7 
 
 Experimental data 7 
 
 Additional data 8 
 
 VA216B experiments 10 
 
 Further work 10 
 
 Conclusions 10 
 
 References 11 
 
 Appendix. — Specific BA4 and VA216 data 12 
 
 ILLUSTRATIONS 
 
 1 . BA4 transducer with horn attached 3 
 
 2 . Cloverleaf grid 4 
 
 3. Free-stream turbulence intensity using cloverleaf grid for turbulence 
 
 generation 5 
 
 4. BA4 calibrations..... 6 
 
 5. VA216B calibration 6 
 
 6. VA216B transducer 6 
 
 7. Ratio of BA4 (corrected for calibration) to HW versus X/M 7 
 
 8. Relative ratio of BA4 (corrected for calibration) to HW versus X/M 8 
 
 9. Ratio of VA216B (corrected for calibration) to HW versus X/M 10 
 
 10. Relative ratio of VA216B (corrected for calibration) to HW versus X/M. . . . 10 
 
 A-l. Pulse frequency versus true velocity for VA216..... 13 
 
 TABLES 
 
 1. Free-stream T. I. downstream of grid using BA4 9061 4 
 
 2. Calibration of BAA 9061, horn removed 5 
 
 3. Calibration of VA216B 7 
 
 4. BA4 9061 ratio of Uba4/Uhw as function of mean speed (HW) for two values 
 
 of X/M, horn removed 8 
 
 5. BA4 9061 with air velocity approximately constant and X/M varied (BA4 
 
 downstream of cloverleaf grid) 9 
 
 3 ; A-l. Calibration 1 of BA4 9050, horn on 12 
 
 A-2. Calibration 2 of BA4 9050, horn on 12 
 
 A-3. Calibration of BA4 9050, horn removed 13 
 
 A-4. Calibration of BA4 9061, horn on 13 
 
 J A-5. Additional calibration of BA4 9061, scale 1, horn on 13 
 
 3 
 

 UNIT OF MEASURE ABBREVIATIONS 
 
 
 ft 
 
 foot in 
 
 inch 
 
 f t/min 
 
 foot per minute m/s 
 
 meter per second 
 
 Hz 
 
 hertz 
 
 
EFFECT OF TURBULENCE ON VORTEX-SHEDDING AIR-VELOCITY TRANSDUCERS 
 
 By A. F. Cohen 1 
 
 ABSTRACT 
 
 When location guidelines are followed in choosing sites for fixed- 
 point velocity transducers for use in underground coal mine monitoring, 
 mine air turbulence intensities <11% are generally expected at those 
 sites. The objective of this Bureau of Mines investigation to determine 
 the effect of turbulence intensities <11% on vortex shedding sensors and 
 transducers. 
 
 Measurements were made at velocity levels of interest for underground 
 coal mine monitoring use ("200, «500, «1,000, «1,500 f t/min) . The ef- 
 fect of grid-produced turbulence intensities (2% to «14%) on the output 
 of vortex-shedding air-velocity transducers was less than ±10%. 
 
 INTRODUCTION 
 
 Underground coal mine air moving at velocities of approximately 200 to 
 1,500 f t/min is turbulent and the presence of such turbulence may affect 
 the output of air-velocity sensors or transducers. Interim performance 
 specifications for fixed-point air-velocity transducers 2 used with the 
 Bureau of Mines Intrinsically Safe Mine Monitoring System (ISMMS) recom- 
 mend 90% accuracy in the velocity range 200 to 1,500 ft/ min. There- 
 fore, the Pittsburgh Research Center, in cooperation with the National 
 Bureau of Standards (NBS), investigated the effect of turbulence inten- 
 sity (T.I.) 3 on transducer output to determine whether turbulence inten- 
 sity had a large (>30%) effect or a relatively small (<10%) effect at 
 mine turbulence levels corresponding to optimal transducer locations in 
 U.S. underground coal mine airways. 
 
 'Physicist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
 
 ^A transducer is a packaged component that is connected to a source of power and 
 delivers an output signal related to the variable being measured. The package con- 
 tains a sensor, signal conditioning circuits, and power conditioning circuits. The 
 sensor is a device that produces an electrical signal in response to a specific 
 parameter, such as air velocity. 
 
 3 RMS average of turbulent component of velocity , 
 T • 1 • — n . — u/U. 
 
 Average velocity 
 
MINE TURBULENCE 
 
 A literature search of expected levels 
 of turbulence in underground coal mines 
 produced few references. Teale Q_) 4 re- 
 ported that mine air fluctuations caused 
 vane anemometers to read high. Teale' s 
 experiments with vane anemometers were 
 conducted in an experimental underground 
 mine gallery of rectangular cross sec- 
 tion, 4 ft 9 in by 6 ft 4 in. His ex- 
 periments indicated that the amount of 
 overestimate of air velocity by vane 
 anemometers was related to the amplitude 
 of fluctuation^ of the air; the greater 
 the amplitude of fluctuation, the greater 
 the overestimate of velocity. An ampli- 
 tude of fluctuation of 30% corresponded 
 to an overestimate of air velocity (by 
 vane anemometer) of 17%. 
 
 Turbulence intensity measurements were 
 performed under a Bureau-sponsored con- 
 tract at the Bureau's Safety Research 
 Coal Mine, Bruceton, PA, at a location 
 consistent with air velocity transducer 
 site guidelines (2^, p. 32). At these 
 locations T.I. was determined at 26 
 equally distributed points representative 
 of «75% of the total («6 ft high by 18 ft 
 wide) cross sectional area (bottommost 
 area near floor was not sampled nor was 
 one side, adjacent to the rib). The 
 average of the 26 T.I.'s measured was 
 «11%. The average T.I. of the center 
 section of the airway (representing four 
 data points) was 6% to 7%. Average air 
 
 velocity through the cross section was 
 «200 ft/min. (Turbulence intensity is 
 one descriptor of turbulence; spectral 
 content and turbulence scale are others.) 
 
 In 1978, a research project at the 
 Bureau's Experimental Mine, Bruceton, PA, 
 obtained T.I. data (on a vertical center 
 line) as a function of distance from the 
 roof to the center of the airway cross 
 section (roof to floor distance was 8 
 ft). In that cross section, T.I. at the 
 center was »3.5% (velocity was 155 
 ft/min); at 0.5 ft/min from the roof, 
 T.I. was 9.4% (velocity was "96 ft/min); 
 at 1 ft from the roof, T.I. was 8% 
 (velocity was 125 ft/min). In this case, 
 T.I. varied monotonically with distance 
 from the roof to the center of the cross 
 section. 
 
 At another location in the same mine 
 (distance from roof to floor was «7 ft) , 
 at the center of the cross section, T.I. 
 was «9.5% (velocity was 165 ft/min); at 
 0.5 ft from roof, T.I. was 7.3% (velocity 
 was «110 ft/min); at 1 ft from the roof, 
 T.I. was «6% (velocity was 125 ft/min); 
 and at 1.5 ft from roof, T.I. was «5% 
 (minimum value) and velocity was "135 
 ft/min. On the basis of the above infor- 
 mation, T.I.'s up to approximately 11% 
 represent a reasonable range for studying 
 the effect of mine T.I. on output of the 
 air-velocity transducer. 
 
 CURRENT INVESTIGATION 
 
 The current investigation involves two 
 types of vortex-shedding transducers: 
 the BA4 Air Velocity Monitor (model MRD 
 69340) by Technitron, Surrey England; and 
 the VA216B Air Draft Sensor by J-Tec As- 
 sociates, Cedar Rapids, IA. 
 
 The BA4 is a system for measuring, in- 
 dicating, and recording air velocity. It 
 
 ^Underlined numbers in parentheses re- 
 fer to items in the list of references 
 preceding the appendix. 
 
 ^Amplitude of fluctuation 
 
 J_ Maximum velocity - minimum velocity . 
 
 2 Mean velocity 
 
 includes the transducer, a control unit, 
 a strip chart recorder, and a battery- 
 power unit. The transducer includes the 
 sensor, which detects vortices created by 
 a fixed-dimension strut by means of ul- 
 trasonics and electronic circuits; the 
 control unit provides electrical power to 
 the transducer and access to the output 
 signal from the transducer. 
 
 The VA216B is a transducer that in- 
 cludes a sensor that detects vortices 
 created by a fixed-dimension strut by 
 means of ultrasonics and the electronic 
 circuits. The VA216B is in use in the 
 
Bureau's ISMMS (_3 ) . An earlier model, 
 the VA216, was very mineworthy under nor- 
 mal mine operating conditions (4^ p. 3). 
 
 The original patent for ultrasonically 
 detecting vortex shedding is held by J- 
 Tec, so some similarities between the J- 
 Tec and the BA4 might be expected; how- 
 ever, there are notable differences. For 
 example, the VA216B sensor strut cross 
 section is cylindrical, whereas that of 
 the BA4 is triangular; also, the BA4 
 transducer includes a shieldlike attach- 
 ment (horn), as shown in figure 1. 
 
 PRINCIPLE OF OPERATION 
 
 Vortices are formed in air passing 
 around an object such as a cylinder. The 
 rate of vortex formation (the frequency) 
 is proportional to air speed. A plot of 
 pulse frequency versus velocity for the 
 VA216 transducer (_5) is shown in appendix 
 figure A-l. The number of vortices 
 formed (or shed by the cylindrical strut) 
 per unit time downwind from the cylinder 
 are counted ultrasonically using a trans- 
 mitter and receiver downstream of the 
 vortex-shedding cylinder. The frequency 
 of vortices shed is independent of en- 
 vironmental factors such as temperature, 
 humidity, and presence of dust, as long 
 as the cross section of the vortex shed- 
 ding element (cylinder, for example) re- 
 mains unchanged. 
 
 An experiment under a Bureau contract 
 (J_, p. 56) indicated that turbulence 
 (T.I. estimated between 20% and 30% at a 
 simulated mine split using a wind tunnel) 
 resulted in an overestimate of air 
 velocity of more than 30% as measured by 
 the VA216B. A hot film anemometer was 
 used as the air-velocity-control instru- 
 ment in the proximity of the VA216B. 
 
 WIND TUNNEL AND TURBULENCE GRID 
 AND T.I. CHARACTERIZATION 
 
 The NBS 5- by 7-ft test section of the 
 dual test section wind tunnel was used 
 for turbulence tests on the BA4 9061, and 
 the VA216B. Turbulence intensities up to 
 and in excess of 10% could be obtained 
 using aluminum "cloverleaf" decorative 
 panels in a specially constructed grid 
 (fig. 2A) . This grid was backed by a 
 second grid identified as an NBS 1-1/4-in 
 woven mesh grid made of 1/4-in-diameter 
 cylindrical rods for support (fig. 25). 
 
 The distance between adjacent centers 
 of the cloverleaf openings is 0.50 in. 
 Therefore, it is assumed that 0.50 in. is 
 the mesh, M, for the cloverleaf grid. 
 Also, X is the distance, in inches, from 
 the grid to the center of the cross sec- 
 tion of the triangular vortex-shedding 
 strut of the BA4. The turbulence inten- 
 sity ratio, u'/U, was measured as a 
 function of X/M for four mean stream 
 
 FIGURE 1. - BA4 transducer with horn attached. A, Overall view; B, front view, showing sensor 
 inside horn. 
 

 
 
 s»>>***»* '- 
 
 
 FIGURE 2;> - Cloverleaf grid* ^4, Upstream side of cloverleaf grid; B, downstream side of cloverleaf 
 grid with l-l/4=in NBS grid in front (appearing as small, connected squares). Panel B shows BA4 with- 
 out horn (bottom of photograph) and hot-wire anemometer (directly above). 
 
 velocities , where U is the mean stream 
 velocity and u* is the RMS average of ve- 
 locity fluctuations about the mean veloc- 
 ity. The data, in the order obtained, 
 are presented in table 1, and a plot of 
 the data is presented in figure 3. 
 
 The turbulence intensity, u'/U, pro- 
 duced by the grid at a given distance, 
 expressed in units of X/M from the 
 screen, is velocity dependent, especially 
 at the lower values of X/M, where the 
 turbulence intensities are the highest 
 
 TABLE 1. - Free-stream T. I. downstream of grid using BA4 9061 
 (M = 1/2 in; 5- by 7-ft wind tunnel) 
 
 U «1,000 
 
 ft/min 
 
 U «500 ft/min 
 
 U «1,500 
 
 ft/min 
 
 U «200 ft/min 
 
 T.I 
 
 X/M 
 
 T.I. 
 
 X/M 
 
 T.I. 
 
 X/M 
 
 T.I. 
 
 X/M 
 
 0.0737 
 
 32 
 
 0.191 
 
 12 
 
 0.0275 
 
 120 
 
 0.1700 
 
 12 
 
 .0617 
 
 40 
 
 .140 
 
 16 
 
 .0320 
 
 96 
 
 .1237 
 
 16 
 
 .0515 
 
 48 
 
 .111 
 
 20 
 
 .0382 
 
 84 
 
 .1014 
 
 20 
 
 .0427 
 
 60 
 
 .0900 
 
 24 
 
 .0424 
 
 72 
 
 .079 
 
 24 
 
 .0352 
 
 72 
 
 .0672 
 
 32 
 
 .0433 
 
 60 
 
 .059 
 
 32 
 
 .0338 
 
 84 
 
 .0536 
 
 40 
 
 .0521 
 
 48 
 
 .048 
 
 40 
 
 .0303 
 
 96 
 
 .0470 
 
 48 
 
 .0576 
 
 40 
 
 .043 
 
 48 
 
 .0261 
 
 120 
 
 .0426 
 
 60 
 
 .0711 
 
 32 
 
 .037 
 
 60 
 
 .0969 
 
 24 
 
 .0403 
 
 72 
 
 .0922 
 
 24 
 
 .0344 
 
 72 
 
 .1467 
 
 16 
 
 .0364 
 
 84 
 
 .1133 
 
 20 
 
 .0325 
 
 84 
 
 .1974 
 
 12 
 
 .0346 
 
 96 
 
 .1476 
 
 16 
 
 .0262 
 
 96 
 
 .1173 
 
 20 
 
 .0276 
 
 120 
 
 .2057 
 
 12 
 
 .0223 
 
 120 
 
20 
 
 a 
 
 • 
 
 
 
 
 
 1 
 
 1 
 
 1 
 
 1 1 1 1 1 
 
 18 
 
 o 
 
 
 
 
 
 
 
 
 KEY 
 o =200 ft/min 
 
 16 
 
 - 
 
 
 
 
 
 
 
 
 • =500 ft/min 
 
 14 
 
 - 
 
 B 
 
 • 
 
 
 
 
 
 
 
 a =1,000 ft/min 
 d =1,500 ft/min 
 
 12 
 
 - 
 
 o 
 
 A 
 
 8 
 
 
 
 
 
 
 - 
 
 10 
 
 - 
 
 
 O 
 
 A 
 
 3 
 
 
 
 
 
 - 
 
 08 
 06 
 04 
 no 
 
 
 
 i 
 
 O 
 
 6 
 
 • 
 
 
 1 
 
 A 
 
 □ 
 • 
 O 
 
 I 
 
 H 
 
 • 
 
 o 
 
 1 
 
 i 
 
 o 
 
 B B 
 
 6 ^ I 1 
 
 TABLE 2. - Calibration of BA4 9061, 
 horn removed 1 » 2 
 
 10 20 30 40 50 60 70 80 90 I00 IIO 1 20 
 DISTANCE FROM GRID, X/M 
 
 FIGURE 3. - Free-stream turbulence intensity 
 using cfoverfeaf grid for turbulence generation. 
 M = 0.50 in. 
 
 (fig. 3). A range of turbulence inten- 
 sity of 2% to «14% was realized with the 
 grid in experiments to be described in 
 this report. 
 
 CALIBRATION OF BA4 AND VA216B 
 
 A linearized hot-wire anemometer (LHWA) 
 was used as a reference velocity-measur- 
 ing device whose mean indication is 
 assumed to be stable and unaffected 
 by high turbulence intensities. Measure- 
 ments were performed in the NBS 5- by 7- 
 ft wind tunnel. The LHWA anemometer, in 
 turn, was calibrated in the NBS low- 
 velocity wind tunnel using a laser veloc- 
 imeter. The low-velocity wind tunnel is 
 the same wind tunnel in which the BA4 
 system was calibrated in 1982. Appendix 
 tables A-l through A-5 show the calibra- 
 tion data obtained in 1982 for the BA4 
 systems 9050 and 9061. A plot of the 0° 
 yaw, 0° pitch calibration data for BA4 
 9050 with horn on (normal state) and also 
 with horn removed is shown in figure 4. 
 The BA4 9061 without horn was recently 
 calibrated in the NBS low-velocity wind 
 tunnel using a laser velocimeter as stan- 
 dard. These data appear in table 2 and 
 are plotted in figure 4. 
 
 True airspeed 
 (V + ), m/s 
 
 Indicated 
 airspeed, 
 (Vj), m/s 
 
 SCALE 1 
 
 SCALE 2 
 
 SCALE 3 
 
 V+/V, 
 
 1.075 
 
 1.00 
 
 1.08 
 
 .9841 
 
 .90 
 
 1.24 
 
 .8722 
 
 .80 
 
 1.09 
 
 .7696 
 
 .70 
 
 1.10 
 
 .6472 
 
 .60 
 
 1.08 
 
 .5335 
 
 .50 
 
 1.07 
 
 .4632 
 
 .40 
 
 1.16 
 
 .3264 
 
 .30 
 
 1.09 
 
 .2657 
 
 .22 
 
 1.21 
 
 1.006 
 
 .80 
 
 1.26 
 
 1.248 
 
 1.20 
 
 1.04 
 
 1.518 
 
 1.50 
 
 1.01 
 
 1.696 
 
 1.70 
 
 .998 
 
 1.971 
 
 2.00 
 
 .996 
 
 2.023 
 
 2.00 
 
 1.01 
 
 1.578 
 
 1.50 
 
 1.05 
 
 1.096 
 
 1.00 
 
 1.10 
 
 .5907 
 
 .50 
 
 1.18 
 
 2.494 
 
 2.50 
 
 .998 
 
 2.917 
 
 3.00 
 
 .972 
 
 3.392 
 
 3.50 
 
 .969 
 
 3.869 
 
 4.00 
 
 .967 
 
 4.349 
 
 4.50 
 
 .966 
 
 4.837 
 
 5.00 
 
 .967 
 
 4.888 
 
 5.00 
 
 0.978 
 
 5.757 
 
 6.00 
 
 .960 
 
 6.909 
 
 7.00 
 
 .987 
 
 7.901 
 
 8.00 
 
 .988 
 
 9.004 
 
 9.00 
 
 1.000 
 
 10.14 
 
 10.00 
 
 1.014 
 
 3.867 
 
 4.00 
 
 .966 
 
 2.916 
 
 3.00 
 
 .972 
 
 2.012 
 
 2.00 
 
 1.006 
 
 1.123 
 
 1.00 
 
 1.123 
 
 'The BA4 instrument seal 
 meters per second, hence pre 
 data of the BA4 and figures 
 the data are in those units. 
 
 2 Data are presented in 
 tained and indicates effect 
 airspeed. 
 
 es are in 
 sentation of 
 illustrating 
 
 order ob- 
 of changing 
 
FIGURE 4. - BA4 calibrations. 
 
 | 1,000 
 
 200 400 600 800 1,000 1,200 1,400 1,600 1,800 
 V(, tt/min 
 
 FIGURE 5.- VA216B calibration. 
 
 FIGURE 6. - VA216B transducer. A, Overall 
 view; B, closeup, showing transmitter {l), cylin- 
 drical strut [2), and receiver (3). 
 
The LHWA is in a fixed position ver- 
 tically above and in the same plane as 
 the sensing element (the strut) of the 
 BA4 9061 and is maintained in the same 
 plane as the BA4 strut as X/M is varied. 
 Movable supports were employed to vary X, 
 hence X/M, yet keep a constant distance 
 (18-1/4 in) between the LHWA and the BA4. 
 Fig. 25 shows the BA4 without horn in the 
 5- by 7-ft test section of the wind 
 tunnel. 
 
 A similar arrangement was used for the 
 VA216B measurements. Calibration data of 
 the VA216B are shown in table 3 and fig- 
 ure 5. Figure 6 shows the VA216B. 
 
 TABLE 3. - Calibration of 
 VA216B, feet per minute 
 
 V, 
 
 i 
 
 56.21 
 
 0.00 
 
 153.6 
 
 73.8 
 
 218.3 
 
 220.8 
 
 300.6 
 
 345.6 
 
 398.0 
 
 450.6 
 
 598.1 
 
 730.8 
 
 792.4 
 
 943.2 
 
 990.6 
 
 1,111 
 
 1,235 
 
 1,331 
 
 1,478 
 
 1,547 
 
 1,737 
 
 1,769 
 
 114.3 
 
 96.0 
 
 139.3 
 
 78.0 
 
 BA4 EXPERIMENTS 
 
 EXPERIMENTAL DATA 
 
 For the first experiments with X/M con- 
 stant, BA4 9061 transducer outputs and 
 concurrent LHWA readings were obtained at 
 four velocity levels. Using the calibra- 
 tion data, calibration corrections to the 
 BA4 output were incorporated in obtaining 
 the following ratio: BA4 (corrected) to 
 LHWA designated as BA4 (corrected) to HW 
 in the graphical presentations. 
 
 The velocity levels («200, «500, 
 « 1,000, « 1,500 ft/min) are not precisely 
 reproduced at a given X/M as the sequenc- 
 ing of measurements at different veloci- 
 ties is made. 
 
 The appreciable increase in BA4/HW out- 
 put (fig. 7) at X/M <30 is attributed to 
 the proximity to the grid of the BA4 horn 
 rather than a turbulence intensity de- 
 pendence of the vortex shedding sensor; 
 i.e., if the BA4 9061 with horn was 
 placed in a mine away from obstructions 
 but where turbulence intensities of the 
 order of 8% to 10% existed, the antici- 
 pated effect would be approximately the 
 same as on the BA4 9061 without horn. 
 One test confirming this assumption con- 
 sisted of removing the horn and deter- 
 mining the ratio of BA4 (corrected) to 
 LHWA at an X/M <30 (cloverleaf grid). In 
 
 figure 7, data without the horn are shown 
 for X/M = 18 and also for X/M = 84; the 
 ratio BA4 (corrected) to LHWA output is 
 largely reduced at X/M = 18 , compared to 
 the case with the horn attached. The 
 data without the horn are presented in 
 table 4, and averages of the data without 
 horn are plotted in figure 7. 
 
 1.6 
 1.5 
 1.4 
 1.3 
 1.2 
 I.I 
 1.0 
 .9 
 .8 
 
 KEY 
 
 Without horn 
 V=200 ft/min 
 V=500 ft/min 
 V=l,000 ft/min 
 V=l,500 ft/min 
 
 =1,500 
 
 x 
 =1,000 ft/min 
 
 = 1,000 ft /mm 
 = 1,500 ft/min' 
 =200ft/min / 
 =500 ft/min' 
 
 10 20 30 40 50 60 70 80 90 
 DISTANCE FROM 6RID, X/M 
 
 FIGURE 7. - Ratio of BA4 (corrected for 
 calibration) to HW versus X/M. 
 
TABLE 4. - BA4 9061 ratio of U BA4 /U HW 
 as function of mean speed (HW) for 
 two values of X/M, horn removed 
 
 U HW , ft/min 1 
 
 U BA4/ U HW 
 
 X/M = 18 
 
 U BA4 
 (corrected) 
 
 nhm. 
 
 206 
 
 0.93 
 
 1.00 
 
 498 
 
 1.14 
 
 1.14 
 
 1,513 
 
 .94 
 
 .93 
 
 969 
 
 .91 
 
 .88 
 
 491 
 
 1.08 
 
 1.08 
 
 206 
 
 .98 
 
 1.05 
 
 973 
 
 .90 
 
 .87 
 
 973 
 
 .91 
 
 .81 
 
 1,497 
 
 .95 
 
 .94 
 
 501 
 
 1.13 
 
 1.13 
 
 208 
 
 .97 
 
 1.04 
 
 1,493 
 
 .95 
 
 .94 
 
 928 
 
 .95 
 
 .95 
 
 515 
 
 1.14 
 
 1.14 
 
 Average: 2 
 
 
 
 «200 
 
 .96 
 
 1.03 
 
 «500 
 
 1.12 
 
 1.12 
 
 «1,000 
 
 .92 
 
 .875 
 
 »1,500 
 
 .95 
 
 .94 
 
 X/M = 84 
 
 567 
 
 0.92 
 
 0.92 
 
 195 
 
 .83 
 
 .89 
 
 969 
 
 .91 
 
 .88 
 
 1,491 
 
 .91 
 
 .90 
 
 193 
 
 .82 
 
 .88 
 
 490 
 
 .93 
 
 .93 
 
 994 
 
 .91 
 
 .88 
 
 1,492 
 
 .92 
 
 .91 
 
 199 
 
 .87 
 
 .94 
 
 492 
 
 .97 
 
 .97 
 
 975 
 
 .93 
 
 .90 
 
 1,518 
 
 .92 
 
 .91 
 
 Average: 2 
 
 
 
 «200 
 
 .84 
 
 .90 
 
 «500 
 
 .93 
 
 .94 
 
 «1,000 
 
 .92 
 
 .92 
 
 «1,500 
 
 .92 
 
 .91 
 
 and indicate effect of changing speed. 
 2 Average velocity levels of above data. 
 
 ADDITIONAL DATA 
 
 Additional data with the BA4 9061 was 
 obtained in a different manner than 
 shown in figure 7. In figure 8, the air 
 
 velocity in the wind tunnel was held 
 quite constant (see table 5) , and the 
 effect of air turbulence intensity of 
 different values on the BA4 output was 
 examined; all else remained constant. 
 This was done by measuring the BA4-to-HW 
 ratios for different X/M, velocity re- 
 maining constant. 
 
 For the present, these data (fig. 8) 
 should be considered "relative" data. 
 After figure 7 experiments, the turbu- 
 lence grid had to be removed from the 
 tunnel to make the tunnel available for 
 use by others. When the experiment was 
 resumed, lower values of BA4 (corrected) 
 to HW were obtained. These lowered val- 
 ues are in part attributable to a change 
 in the HW anemometer calibration. In any 
 case, the effect of grid-produced turbu- 
 lence does not appreciably affect the 
 output of the BA4 vortex shedding device 
 (effect is <±10% about the mean BA4 (cor- 
 rected) /HW) between T.I. = 2% and «12% at 
 either 200 fpm or 500 fpm velocity level. 
 
 Figure 8 includes BA4 9061 data with 
 horn attached and with horn removed at 
 air velocities of approximately 200 and 
 500 ft/min. With horn attached, keeping 
 the velocity constant and altering X/M 
 results in the plots of the (relative) 
 ratio BA4 (corrected for 
 to HW versus X/M. The 
 in output (fig. 8) at 
 500 ft/min for X/M <20 
 are very comparable to those in figure 7 
 (horn attached) and are attributed to the 
 horn's proximity to the grid. 
 
 1.5 
 
 BA calibration) 
 large increase 
 both 200 and 
 
 (horn attached) 
 
 1.4 
 
 1.0 
 
 KEY 
 l A =200 ft/min 
 
 \o =500 ft/min 
 /«=500ft/min (horn removed) 
 
 ln=200ft/min (horn removed) 
 
 "10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 
 DISTANCE, X/M 
 
 FIGURE 8. - Relative ratio of BA4 (corrected 
 for calibration) to HW versus X/M. 
 
TABLE 5. - BA4 9061 with air velocity approximately constant and X/M 
 varied (BA4 downstream of cloverleaf grid) 
 
 U HW» , 
 
 
 
 BA4 
 
 U HW> , 
 
 
 
 BA4 
 
 ft/min 1 
 
 X/M 
 
 BA4/HW 
 
 (corrected)/ 
 HW 
 
 ft/min 1 
 
 X/M 
 
 BA4/HW 
 
 (corrected)/ 
 HW 
 
 SB 
 
 200 ft/min, i N 
 
 SB 
 
 500 ft/min, HORN ON 
 
 189 
 
 14 
 
 1.24 
 
 1.39 
 
 513 
 
 28 
 
 0.855 
 
 0.829 
 
 193 
 
 16 
 
 1.02 
 
 1.14 
 
 514 
 
 13 
 
 1.48 
 
 1.44 
 
 206 
 
 18 
 
 .959 
 
 1.06 
 
 519 
 
 16 
 
 1.20 
 
 1.16 
 
 204 
 
 20 
 
 .878 
 
 .975 
 
 522 
 
 18 
 
 1.07 
 
 1.04 
 
 208 
 
 22 
 
 .844 
 
 1.03 
 
 518 
 
 20 
 
 .971 
 
 .942 
 
 209 
 
 24 
 
 .805 
 
 .886 
 
 516 
 
 48 
 
 .850 
 
 .825 
 
 207 
 
 28 
 
 .794 
 
 .873 
 
 512 
 
 40 
 
 .840 
 
 .815 
 
 208 
 
 32 
 
 .775 
 
 .853 
 
 511 
 
 48 
 
 .823 
 
 .798 
 
 213 
 
 40 
 
 .748 
 
 .823 
 
 507 
 
 130 
 
 .812 
 
 .788 
 
 208 
 
 48 
 
 .721 
 
 .793 
 
 512 
 
 160 
 
 .803 
 
 .780 
 
 209 
 
 60 
 
 .718 
 
 .790 
 
 506 
 
 28 
 
 .849 
 
 .823 
 
 206 
 
 84 
 
 .722 
 
 .789 
 
 507 
 
 14 
 
 1.48 
 
 1.44 
 
 205 
 
 130 
 
 .740 
 
 .821 
 
 514 
 
 60 
 
 .783 
 
 .760 
 
 204 
 
 160 
 
 .761 
 
 .845 
 
 515 
 
 22 
 
 .870 
 
 .844 
 
 213 
 
 28 
 
 .774 
 
 .851 
 
 501 
 
 160 
 
 .803 
 
 .780 
 
 213 
 
 14 
 
 1.24 
 
 .36 
 
 506 
 
 40 
 
 .800 
 
 .776 
 
 197 
 
 22 
 
 .843 
 
 1.936 
 
 502 
 
 28 
 
 .820 
 
 .795 
 
 205 
 
 60 
 
 .714 
 
 .793 
 
 502 
 
 16 
 
 1.15 
 
 1.12 
 
 207 
 
 160 
 
 .751 
 
 .832 
 
 
 
 
 
 206 
 
 40 
 
 .736 
 
 .816 
 
 
 
 
 
 202 
 
 28 
 
 .770 
 
 .855 
 
 
 
 
 
 «2 
 
 00 ft 
 
 /min, H 
 
 ORN OFF 
 
 «500 ft/min, HORN OFF 
 
 191 
 
 14 
 
 0.850 
 
 0.913 
 
 504 
 
 16 
 
 0.835 
 
 0.835 
 
 202 
 
 16 
 
 .815 
 
 .876 
 
 487 
 
 14 
 
 .882 
 
 .882 
 
 199 
 
 18 
 
 .826 
 
 .888 
 
 496 
 
 18 
 
 .848 
 
 .848 
 
 195 
 
 20 
 
 .836 
 
 .899 
 
 514 
 
 20 
 
 .819 
 
 .819 
 
 198 
 
 22 
 
 .842 
 
 .905 
 
 520 
 
 22 
 
 .791 
 
 .791 
 
 203 
 
 14 
 
 .821 
 
 .883 
 
 521 
 
 24 
 
 .790 
 
 .790 
 
 194 
 
 28 
 
 .755 
 
 .812 
 
 514 
 
 32 
 
 .783 
 
 .783 
 
 201 
 
 32 
 
 .774 
 
 .832 
 
 522 
 
 40 
 
 .779 
 
 .779 
 
 204 
 
 40 
 
 .737 
 
 .792 
 
 517 
 
 48 
 
 .779 
 
 .779 
 
 203 
 
 48 
 
 .739 
 
 .794 
 
 507 
 
 60 
 
 .794 
 
 .794 
 
 197 
 
 50 
 
 .772 
 
 .830 
 
 503 
 
 84 
 
 .801 
 
 .801 
 
 199 
 
 84 
 
 .781 
 
 .840 
 
 505 
 
 130 
 
 .797 
 
 .797 
 
 204 
 
 130 
 
 .778 
 
 .837 
 
 512 
 
 160 
 
 .804 
 
 .804 
 
 207 
 
 160 
 
 .779 
 
 .837 
 
 514 
 
 28 
 
 .782 
 
 .782 
 
 200 
 
 28 
 
 .759 
 
 .816 
 
 
 
 
 
 Data are presented in order obtained and indicate effect of changing 
 
 airspeed, 
 
 With the horn removed, at X/M <30, 
 the relative ratio of BA4 (corrected 
 for BA4 calibration) to HW remains near- 
 ly constant (T.I. increasing from «6% 
 to 12% between X/M = 30 to X/M = 14, 
 respectively) . 
 
 The most important finding is that 
 T.I.'s of 2% to "14% employed in this in- 
 vestigation affect the output of the BA4 
 very little (less than ±10% about the 
 mean BA4/HW output) at each of the veloc- 
 ity levels investigated. 
 
10 
 
 VA216B EXPERIMENTS 
 
 As with the BA4 system, the first ex- 
 periments with the VA216B transducer were 
 conducted at constant X/M and the veloc- 
 ity level was varied (four levels). The 
 data were obtained a few days after the 
 data of figure 7 (BA4 system) and are 
 shown in figure 9. The results are not 
 unlike those with the BA4 system ob- 
 tained in a similar manner (not absolute 
 equilibrium) . 
 
 Later, data were obtained with the 
 VA216B in the same way and under compara- 
 ble conditions as those of figure 8 (BA4 
 system). Figure 10 shows these VA216B 
 data in which a specific velocity was 
 held constant for an extended period and 
 X/M was varied. The effect of varying 
 only the T.I. is indicated. 
 
 For a given velocity level (e.g., 1,500 
 f t/min) , the variations in VA216B (cor- 
 rected) to HW over the range of X/M (14 
 to 160) corresponding to T.I. (12% to 2%) 
 are less than ±10% about the mean [VA216B 
 ( corrected) /HW] value at 1,500 f t/min. 
 
 When used as a fixed-point transducer 
 for a mine monitoring system such as the 
 Bureau's ISMMS, where a given velocity 
 level is maintained for days or weeks , 
 
 1.4 
 1.3 
 1.2 
 I.I h 
 
 m 
 
 2 i.o 
 
 .9 
 
 
 1 
 
 1 
 
 i ' l 
 
 KEY 
 
 i i i 
 
 1 
 
 - 
 
 
 o 
 
 =200 ft/min 
 
 
 _ 
 
 
 
 • 
 
 =500 ft/min 
 
 
 
 _ 
 
 O o 
 
 A 
 
 = 1,000 ft/min 
 
 
 _ 
 
 
 6 
 
 D 
 
 -1,500 ft/min 
 
 
 
 — 
 
 
 8 
 
 D 
 
 8 
 8 
 
 
 — 
 
 
 J 
 
 A 
 
 o 
 
 o 
 
 j 
 
 
 
 
 
 8 
 
 
 
 1 
 
 i 
 
 i,i, 
 
 i 1 
 
 < 
 
 20 40 60 80 
 
 DISTANCE, X/M 
 
 100 
 
 120 
 
 FIGURE 9. - Ratio of VA216B (corrected for 
 calibration) to HW versus X/M. 
 
 5 1.2 
 
 KEY 
 o =200 ft/mm 
 • =500 ft/min 
 a =1,000 ft/mm 
 a =1,500 fl/min 
 
 s 
 
 20 
 
 60 80 100 
 
 DISTANCE, X/M 
 
 FIGURE 10. - Relative ratio of VA216B (cor- 
 rected for calibration) to HW versus X/M. 
 
 the VA216B output changes due to T.I.'s 
 up to 11% would be small (<±10%). 
 
 FURTHER WORK 
 
 The spectral content of the grid- 
 produced turbulence is under investiga- 
 tion. The effect of turbulence scale on 
 vortex-shedding transducers has not been 
 measured but was considered in the choice 
 
 of grid used in experiments reported 
 here. Turbulence scale and low-frequency 
 fluctuations and/or pulsations of the air 
 in mines has yet to be characterized. 
 
 CONCLUSIONS 
 
 The most important finding of the pres- 
 ent investigation is that grid-produced 
 T.I.'s of 2% to K 14% employed in this in- 
 vestigation affect the output of the BA4 
 system very little — on the order of ±10% 
 or less over the range of conditions 
 tested. 
 
 Similarly, grid-produced T.I.'s (ap- 
 proximately 2% to 14%) affect the out- 
 put of a VA216B transducer less than 
 ±10% at velocity levels 200 to 1,500 
 ft/min. 
 
11 
 
 REFERENCES 
 
 1. Teale, R. The Accuracy of Vane An- 
 emometers in the Measurement of Mine Air- 
 flow. Nat. Coal Board MRE Rep. 2040, 
 1956, 20 pp. 
 
 2. Kohler, J. An Evaluation of the 
 Air Velocity Sensing Unit in the Bureau 
 of Mines Remote Monitoring System con- 
 tract J0308027, Ketron, Inc.). Mar. 1, 
 1982, 57 pp; available from A. F. Cohen, 
 BuMines, Pittsburgh, PA. 
 
 3. Fisher, T. J. , and M. Uhler. Re- 
 search To Develop an Intrinsically Safe 
 Monitoring System for Coal Mines. Paper 
 
 in Proceedings of the Fifth West Virginia 
 University Conference on Coal Mine Elec- 
 tro technology (Morgantown, WV, July 30- 
 31, Aug. 1, 1980). West Virginia Univ., 
 Morgantown, WV, 1980, pp. 20-1 to 20-11. 
 
 4. Scott, L. W. Remote Monitoring of 
 Air Quality in Underground Mines. Bu- 
 Mines RI 8253, 1977, 14 pp. 
 
 5. Purtell, L. P. Low Velocity 
 Performance of Anemometers (contract 
 H0166198, NBS). NBSIR 79-1759, May 1979, 
 169 pp. 
 
12 
 
 APPENDIX. —SPECIFIC BA4 AND VA216 DATA 
 
 Tables A-l through A- 5 show the 0° yaw, 
 0° pitch calibration data for the BA4 
 9050 and 9061. 
 
 TABLE A-l. - Calibration l 1 
 BA4 9050, horn on 
 
 of 
 
 Figure A-l is a plot of pulse frequency 
 versus true velocity (VA216) from NBS 79- 
 1759 data and tables H-l through H-5 (5). 
 
 TABLE A-2. - Calibration 2 1 of 
 BA4 9050, horn on 
 
 V + , m/s 
 
 i » 
 
 m/s 
 
 SCALE 2 
 
 SCALE 3 
 
 V t /V| 
 
 
 SCALE 1 
 
 
 0.307 
 
 0.10 
 
 3.07 
 
 .490 
 
 .41 
 
 1.20 
 
 .994 
 
 .90 
 
 1.10 
 
 1.52 
 
 1.50 
 
 1.01 
 
 1.95 
 
 2.00 
 
 .976 
 
 0.492 
 
 0.30 
 
 1.64 
 
 .990 
 
 .90 
 
 1.10 
 
 1.51 
 
 1.45 
 
 1.04 
 
 1.96 
 
 1.95 
 
 1.01 
 
 2.47 
 
 2.50 
 
 .989 
 
 3.01 
 
 3.20 
 
 .941 
 
 3.98 
 
 4.40 
 
 .904 
 
 4.53 
 
 5.00 
 
 .906 
 
 0.997 
 
 0.90 
 
 1.11 
 
 1.51 
 
 1.40 
 
 1.08 
 
 1.96 
 
 2.00 
 
 .979 
 
 2.47 
 
 2.50 
 
 .989 
 
 3.00 
 
 3.10 
 
 .968 
 
 3.97 
 
 4.30 
 
 .925 
 
 4.56 
 
 5.00 
 
 .913 
 
 4.97 
 
 5.50 
 
 .904 
 
 5.94 
 
 6.50 
 
 .914 
 
 7.94 
 
 8.60 
 
 .924 
 
 9.38 
 
 10.00 
 
 .938 
 
 'Dropout speed, increasing = 
 0.307 m/s; dropout speed, de- 
 creasing = 0.300 m/s; pressure = 
 744 mm Hg; temperature = 22.7° C. 
 
 r t» 
 
 m/s 
 
 i » 
 
 m/s 
 
 SCALE 2 
 
 SCALE 3 
 
 V + /V 
 
 
 SCALE 1 
 
 
 0.302 
 
 0.27 
 
 1.12 
 
 .505 
 
 .46 
 
 1.10 
 
 1.01 
 
 .93 
 
 1.09 
 
 1.52 
 
 1.48 
 
 1.03 
 
 1.98 
 
 2.00 
 
 .990 
 
 0.503 
 
 0.40 
 
 1.26 
 
 1.02 
 
 .95 
 
 1.07 
 
 1.52 
 
 1.48 
 
 1.02 
 
 1.95 
 
 2.00 
 
 .976 
 
 2.49 
 
 2.55 
 
 .977 
 
 2.97 
 
 3.10 
 
 .956 
 
 3.72 
 
 4.00 
 
 .931 
 
 4.56 
 
 5.00 
 
 .912 
 
 1.01 
 
 0.98 
 
 1.03 
 
 1.52 
 
 1.50 
 
 1.01 
 
 1.96 
 
 2.00 
 
 .982 
 
 2.50 
 
 2.60 
 
 .960 
 
 2.97 
 
 3.20 
 
 .928 
 
 3.71 
 
 4.05 
 
 .916 
 
 4.59 
 
 5.00 
 
 .918 
 
 5.36 
 
 5.90 
 
 .908 
 
 7.42 
 
 7.90 
 
 .939 
 
 9.54 
 
 10.00 
 
 .954 
 
 dropout 
 0.302 m/s; 
 creasing = 
 760 mm Hg; 
 
 speed, inc 
 Dropout s 
 0.284 m/s; 
 temperature 
 
 reasing = 
 peed, de- 
 pressure = 
 = 20.2° C. 
 
13 
 
 TABLE A-3. - Calibration 1 of BA4 9050, 
 horn removed 
 
 TABLE A-4. - Calibration 1 of BA4 9061, 
 horn on 
 
 V + , m/s 
 
 Vj , m/s 
 
 V + /Vj V+, m/s 
 
 i > 
 
 m/s 
 
 V+/V, 
 
 
 SCALE 1 
 
 
 0.295 
 
 0.26 
 
 1.13 
 
 .508 
 
 .46 
 
 1.10 
 
 1.02 
 
 .92 
 
 1.11 
 
 2.03 
 
 2.00 
 
 1.01 
 
 
 SCALE 2 
 
 
 0.516 
 
 0.45 
 
 1.15 
 
 1.02 
 
 .90 
 
 1.13 
 
 2.02 
 
 2.00 
 
 1.01 
 
 3.08 
 
 3.10 
 
 .992 
 
 4.91 
 
 5.00 
 
 .981 
 
 
 SCALE 3 
 
 
 1.03 
 
 0.98 
 
 1.05 
 
 2.02 
 
 2.00 
 
 1.01 
 
 3.07 
 
 3.10 
 
 .981 
 
 4.90 
 
 5.00 
 
 .980 
 
 7.02 
 
 7.05 
 
 .996 
 
 10.20 
 
 10.00 
 
 1.02 
 
 'Dropout speed 
 dropout speed, 
 pressure = 751 
 21.2° C. 
 
 320 
 
 , increasing = 
 decreasing = 
 mm Hg ; temp 
 
 0.295 m/s; 
 0.289 m/s; 
 erature = 
 
 280 
 
 240- 
 
 200- 
 
 >- 
 
 UJ 
 
 o 
 
 160 
 
 120 
 
 200 400 600 800 1,000 1,200 1,400 
 
 FIGURE A-l. - Pulse frequency versus true 
 velocity for VA216. 
 
 
 SCALE 1 
 
 
 0.275 
 
 0.22 
 
 1.25 
 
 .493 
 
 .42 
 
 1.17 
 
 1.02 
 
 .90 
 
 1.12 
 
 1.50 
 
 1.46 
 
 1.03 
 
 1.99 
 
 2.00 
 
 .993 
 
 SCALE 2 
 
 0.500 
 
 0.35 
 
 1.43 
 
 1.00 
 
 .90 
 
 1.11 
 
 1.49 
 
 1.45 
 
 1.03 
 
 1.98 
 
 1.95 
 
 1.01 
 
 2.51 
 
 2.52 
 
 .996 
 
 3.03 
 
 3.15 
 
 .960 
 
 3.98 
 
 4.30 
 
 .925 
 
 4.58 
 
 5.00 
 
 .915 
 
 SCALE 3 
 
 1.01 
 
 0.90 
 
 1.12 
 
 1.51 
 
 1.40 
 
 1.08 
 
 1.98 
 
 1.95 
 
 1.01 
 
 2.50 
 
 2.55 
 
 .979 
 
 3.01 
 
 3.10 
 
 .972 
 
 3.99 
 
 4.25 
 
 .938 
 
 4.95 
 
 5.30 
 
 .933 
 
 5.97 
 
 6.35 
 
 .940 
 
 7.92 
 
 8.20 
 
 .966 
 
 9.77 
 
 10.00 
 
 .977 
 
 1 Dropout speed 
 dropout speed, 
 pressure = 755 
 18.7 °C. 
 
 , increasing = 0.275 m/s; 
 decreasing = 0.261 m/s; 
 mm Hg; temperature = 
 
 TABLE A-5. - Additional calibration 1 
 BA4 9061, scale 1, horn on 
 
 of 
 
 V + , m/s 
 
 V| , m/s 
 
 V + /V, 
 
 0.286 
 
 0.22 
 
 1.30 
 
 .361 
 
 .30 
 
 1.20 
 
 .440 
 
 .37 
 
 1.19 
 
 .510 
 
 .43 
 
 1.19 
 
 .605 
 
 .52 
 
 1.16 
 
 .692 
 
 .61 
 
 1.13 
 
 .800 
 
 .71 
 
 1.13 
 
 .902 
 
 .81 
 
 1.11 
 
 1.02 
 
 .90 
 
 1.13 
 
 1.28 
 
 1.18 
 
 1.09 
 
 1.50 
 
 1.45 
 
 1.04 
 
 1.80 
 
 1.77 
 
 1.02 
 
 1.96 
 
 2.00 
 
 .981 
 
 Pressure 
 19.3° C. 
 
 = 761 ram Hg; temperature = 
 
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