rations

a 1 1 1 0

IMBSIR 78-1561

Low Velocity Performance of

an Impact-Deflection

Anemometer

L. P. Purtell

National Bureau of Standards

Fluid Engineering Division

Washington, D.C. 20234

November 1978

Task Report on

Contract No. HOI 661 98

Evaluation of the Behavior of Mine Anemometers in the NBS Low

Velocity Calibration Facility

-PC

100

, U56

78-1561

Prepared for United States Department of the Interior

Bureau of Mines

NaKona! Burgan of Sfatrfart* MAY 1 4 v3-t«

NBSIR 78-1561

i. * LOW VELOCITY PERFORMANCE OF

AN IMPACT-DEFLECTION

ANEMOMETER

L. P. Purtell

Fluid Engineering Division

Center for Mechanical Engineering

and Process Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

November 1978

Task Report

Prepared for United States Department of the Interior

Bureau of Mines

U S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch. Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Erneat Ambler, Director
DISCLAIMER NOTICE

The views and conclusions contained in this document should not be

interpreted as necessarily representing the official policies or recommendations of the Interior Department's Bureau of Mines.
NBS-114A (REV. 5-78)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 78-1561

2. Gov’t Accession

No.

3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

LOW VELOCITY PERFORMANCE OF AN IMPACT-DEFLECTION ANEMOMETER

5. Publication Date

j 6. Performing Organization Code

7. AUTHOR(S)

L. P. Purtell

8. Performing Organ. Report No. NBSIR 78-1561

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 7320483

11. Contract/Grant No. H0166198

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Office of the Assistant Director - Mining

Bureau of Mines

United Stated Department of the Interior

Washington, D.C. 20241

13. Type of Report & Period

Covered

Dec . 1 , 1977-Jan. 31, 1978

14. Sponsoring Agency Code

5. SUPPLEMENTARY NOTES

6. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

Performance of an impact-deflection anemometer is evaluated over the speed

range of 42.3 to 709 feet per minute for five combinations of velocity probes

and velocity ranges. The tests were performed in the NBS Low Velocity Airflow

Facility which provides a uniform flow of low turbulence and utilizes a laser

velocimeter as the velocity standard.

7. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first kev word unless a proper name; separated by semicolons)

Airflow; anemometer; laser velocimeter; mine ventilation; low velocity; wind tunnel.

8. AVAILABILITY ^

Unlimited 19. SECURITY CLASS

(THIS REPORT)

21. NO. OF PAGES

j

For Official Distribution. Do Not Release to NTIS

UNCLASSIFIED

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Washington1_D.C. 20402. SD Stock No. SN003-003

20. SECURITY CLASS

(THIS PAGET

22. Price

— Order From National Technical Information Service (NTIS)

Springfield, Virginia 22161 UNCLASSIFIED

JSCOMM-OC SS630 ? 1
FOREWORD

This report was prepared by the National Bureau of Standards,

Fluid Engineering Division, Washington, D. C. 20234, under USBM

Contract Number H0166198. The contract was initiated under the

Coal Mine Health and Safety Program. It was administered under the

technical direction of PM&SRC, with Dr. George H. Schnakenberg , Jr.,

acting as the Technical Project Officer. Mr. H. R. Eveland was the

contract administrator for the Bureau of Mines.

This report is a summary of the work recently completed as part

of this contract during the period December 1, 1977 to January 31,

1978. This report was submitted by the author November 1978.

2
LIST OF SYMBOLS

U

U

u

u

if

U.

1

a

c

R.

1

R

velocity measured by laser velocimeter

velocity indicated by anemometer under test

line segments fitted to U, data

group mean true velocity

group mean indicated velocity

standard deviation of U. data from U.,.

1 if

standard deviation of U. data expressed as true

velocity

a adjusted for known variance in laser

velocimeter measurements

resolution of the instrument

resolution expressed as true velocity

r

3
LOW VELOCITY PERFORMANCE OF AN

IMPACT-DEFLECTION ANEMOMETER

L. P. Purtell

1. INTRODUCTION

The National Bureau of Standards in order to meet the need for a calibration capability with adequate accuracy at low air velocities,

i.e., below 500 feet per minute (fpm) undertook the development of a low-velocity calibration facility for wind speed measuring instruments

which would provide a capability down to 3 meters per minute (approximately 10 fpm) with an accuracy of plus or minus one percent. It was a natural consequence therefore that when said facility became operational

to undertake an evaluation of the state-of-the-art and to provide the

information needed as to the reliability and performance of instrumentation for such measurement. Accordingly, a number of prototypes of

various types of instruments for low velocity air measurements are undergoing test at NBS, and this report is concerned specifically with

the results of one such test.

2 . THE INSTRUMENT

The anemometer tested for this report is a commercially available

instrument (Alnor Instrument Company, Velometer, Series 6000-P) 1 used

in the mining industry and elsewhere as a portable anemometer. It was supplied for test by the U. S. Mining Enforcement and Safety Administration at the request of the U. S. Bureau of Mines. The instrument

(approximately 15 x 17 x 6 cm) contains an impact-deflection mechanism

which deflects the needle indicator of a meter in response to the impact pressure from the airflow and consists of a main body meter with

connections for one of several probes. The Pitot probe is composed

of a cylinder 0.5 inches in diameter and 13 inches long which mounts in

a range selector unit connected to the main body by hoses (Figure 1)

.

The cylinder has ports to admit the airflow and must be properly oriented

in the airstream to obtain a reading. The range selector may be set to one of two ranges, 100-1250 fpm (low range) and 100-2500 fpm (high range).

Other range selectors are available, but were not tested herein.

The diffuser probe (Figure 2) is similar to the Pitot probe except

that only impact pressure is utilized in the diffuser probe thus requiring

a vent to be opened in the range selector for operation. It operates

over the same ranges as the Pitot probe.

This particular instrument was selected as being representative of

this type of anemometer and its selection does not represent an endorsement

.

4
The low velocity probe (Figure 3.) attaches directly to the main body

and operates like the Pitot probe except over a range of 30-300 fpm.

Note that all the probes and the main body were mounted entirely within

the wind tunnel since the flow is slightly below atmospheric pressure.

3. THE TEST

The NBS Low Velocity Airflow Facility [1] used to test this instrument generates a low velocity air stream having a low turbulence intensity (less than 0.05%) and a large region of uniform flow (at least 75 x

75 cm). A laser velocimeter is employed as a primary velocity standard.

It is nonintrusive, has a linear response with velocity, and has good

spatial resolution. Adequate sensitivity is obtained without the artifi

cial seeding of scattering particles. Thus, the difficulties and inconvenience associated with seeding and the possible effect of such seeding

on the performance of the device under test are avoided.

The anemometer was mounted on the centerline of the tunnel test

section one meter downstream of the entrance to the test section in a manner to minimize the effect of the support on the air stream around

the anemometer (Figures 1-3) . Since the anemometer itself modifies the

airflow in the tunnel, the velocity should be measured at a location in

the flow which has the same velocity in the presence of the anemometer

as it does in the absence of the anemometer. Since both the Pitot probe

and the diffuser probe have small projected areas and are cylindrical, a distance of 30 cm upstream of the probes was chosen as the location for

the laser velocimeter probe volume. Since 30 cm is approximately 24

diameters, disturbance to the flow should not be perceptible. This

distance, 30 cm, has also been used for other tests (eg., [2]). The

low velocity probe set-up, however, is quite large since the main body i

attached directly to the probe. Thus measurements were made of the air

velocity, U, at various distances upstream of the anemometer on the

tunnel centerline at a freestream speed, U , of 70 fpm. The ratio

U/U^ is plotted in Figure 4 and shows that within the accuracy of

the measurements (about 1%) the presence of the anemometer is not

noticeable beyond about 25 cm. Thus, again 30 cm upstream of the

anemometer was chosen as the location of the laser velocimeter probe

volume. With no anemometer in the tunnel variation in velocity along

the centerline is imperceptible over the distance traversed.

The air speed indicated by the anemometer was recorded during

the time interval required for the measurement by the laser velocimeter.

If fluctuations of the dial indicator were noticeable their magnitude

was estimated and recorded. Five separate test runs were made for each

speed range, and for each probe, a run consisting of eight different

velocities for the Pitot and diffuser probes and seven for the low

velocity probe. The lowest velocities were limited by instrument

resolution and are 100 fpm for the low and high ranges and 40 fpm for

the low velocity probe. The data are presented in chronological order

in Tables 1A to IE through 5A to 5E.

5
4. TEST RESULTS

Since a particular air speed in the wind tunnel cannot be exactly

reset from run to run, scatter in the test data is distributed along a curve, thus prohibiting computing the standard deviation of the data

from a simple average. Instead, deviations from a curve fit to the data

were computed and the standard deviation approximated by the r.m.s. value of these deviations within a group. The groups are:

Pitot probe, low range, fpm Pitot probe, high range, fpm

U < 120 U < 120

120 < u < 170 120 < u < 170

170 < u < 250 170 < u < 250

250 < u < 350 250 < u < 350

350 < u < 450 350 < u < 450

450 < u < 550 450 < u < 550

550 < u < 650 550 < u < 650

650 < u 650 < u

Diffuser probe, low range, fpm

U < 120

120 < u < 170

170 < u < 250

250 < u < 350

350 < u < 450

450 < u < 550

550 < u < 650

650 < u

Diffuser probe, high range, fpm

U < 120

120 < u < 170

170 < u < 250

250 < u < 350

350 < u < 450

450 < u < 550

550 < u < 650

650 < u

Low velocity probe, fpm

U < 50

50 < u < 60

60 < u < 90

90 < u < 120

120 < u < 170

170 < u < 220

220 < u

6
Since the groups of data are compact (small range of U within a group; see Figures 5 through 9, a straight line segment is used to approximate

the curve within a group. The line segment passes through the point

(U,U.), the group mean true velocity and the group mean indicated velocity.

The slope of the line segment is computed as the average of the slopes

of two lines, both passing through (U,U.) of the groups being considered,

one line passing through the (U,U.) of the adjacent group higher in

velocity, and one line passing through (U,U.) of the adjacent group

lower in velocity. For the highest group oi each test there is only one adjacent group, and thus the line segment for this highest group passes

through (U,U.) of that adjacent group. The line segments for the lowest

groups are similarly formed.

Designating the above line segments as U_^, the standard deviation,

O', of the indicated velocity, U., about the fitted segments is

determined by squaring the differences between the 1L data and U^,

i.e., [U.(U) - u

if

(U)

2

. Since the data within the specified groups are reasonably compact, the mean of the squared differences within a group

is taken as an estimate of the variance of U. about U. f within that group

and specified at that group's mean true velocity, U. To convert this to a standard deviation in terms of true velocity, designated O, each G. (U)

is divided by the slope (dlL^/dU) of the line segment associated witfi the

G. (U) . Note that this o does not include the "scatter" in the U measurements (due to the inability to exactly reset the wind tunnel to a specified

speed) , but does include the uncertainty in a particular laser velocimeter

measurement. This uncertainty may be estimated from repeated measurements

of velocity at a particular fan setting, thus also including any unsteadiness

in the velocity, and is estimated as 0.001U for this report. A standard

deviation, O , corrected for the laser velocimeter uncertainty may thus

be computed £rom

a

2 = G2 - (0.001U) 2

for any given U. O and O are presented in Figures 10 through 14 as velocity and in Figures 1§ through 19 as percentage of U. Since ± 20^

is extremely close to the 95 percent confidence interval for one measurement,

curves of ± 2o are also included in Figures 5 through 9 as dashed

lines . C

The actual differences between the true and indicated velocities,

U - U., are presented in Figures 20 through 24 and as a percentage of

U in figures 25 through 29. The curves shown in each figure have been

drawn for reference only.

5. DISCUSSION OF RESULTS

Computing O from measurements by an instrument having a scale with a resolution, R., much smaller than O. is a good procedure for determining

repeatability1of the instrument. 13: the resolution is large ^poor)

compared to G_^ (where is presumed known by some means independent of

7
the scale being considered, say by a second scale with better resolution),

the indicated Cf may be much smaller than it should be. For a Gaussian

distribution of errors it is assumed that a . may be adequately computed

if the resolution is at most approximately izwice a. . The following

values of resolution were judged to be the best that can be read on the

anemometer tested:

Low Range

100 < u.

1

< 200 f pm, R.=

X 1 division or 2Cl fpm

200 < u.

1 < 600 f pm, R . =

l

1/2 division or 10 fpm

600 < u.

1 < 1250 fpm. R.=l

1/4 division or 5 fpm

High Range

100 < u.

1 < 500 fpm, R.=l

1/2 division or 25 fpm

500 < u.

1 < 2500 fpm, R.=l

1/5 division or 10 fpm

Low Velocity Probe

20 < u.

1 < 200 fpm. R . =

l

1/2 division or 2.5 fpm

200 < u.

1

< 300 fpm, R.=

l

1/5 division or 1 fpm

As with the computed values of a., these values of resolution, R. were

converted to equivalent values, ft, in terms of true velocity by dividing

by the slope (dlh^/dU). These latter values, divided by two, were then

included in Figures 10 through 14 in units of velocity and in Figures 15

through 19 as percentage of U. As may be seen in Figures 10 through 14,

R/2 does indeed exceed a for most of the measurements. Thus these

values of a should be taken with reservation and perhaps replaced by the

values R/2. The performance of the instrument in these instances in

terms of repeatability may exceed the quality of its resolution.

The instrument in general performed with no erratic behavior. Some

general comments concerning application of the instrument follow. With

any measurement problems the instrument's capabilities should be matched

to the required measurement.

This anemometer is intrusive, i.e., it must be placed in the flow.

This anemometer is entirely mechanical and does not require an outside

source of power.

Many factors that can affect the suitability of an instrument for a particular application, such as turbulence or unsteadiness of the air

stream, rough handling (shock and vibration), dirt and other environmental

factors, time, orientation to the velocity and gravity vectors, etc.,

have not been tested herein but should be considered.

8
6 . SUMMARY

The performance of an impact-deflection anemometer has been evaluated at air speeds up to 709 fpm. Evaluation of the repeatability was found to involve considering the resolution of the instrument.

Figures are presented showing the deviation of indicated velocity from

true velocity and the standard deviation of repeated runs about the mean

curves. The lowest velocities measurable were limited by resolution

of the instrument and were 100 fpm for the low and high ranges and 40 fpm

for the low velocity probe.

7. REFERENCES

1. L. P. Purtell and P. S. Klebanoff, The NBS Low Velocity Airflow

Facility, in preparation.

2. L. P. Purtell, Low Velocity Performance of a Bronze Bearing Vane

Vane Anemometer, NBSIR 781433.

9
Table 1A

Alnor Velometer

Series 6000-P

Pitot probe-1250 Scale

Indicated Air Speed,

fpm

True Air Speed,

fpm

100

140

190

285

380

102

153

198

297

400

468

560

645

498

603

705

T = 21.1 °C

B = 739.5 mm Hg

Table IB

Alnor Velometer

Series 6000-P

Pitot probe-1250 Scale

Indicated Air Speed, True Air Speed

fpm fpm

100 102

140 154

190 199

280 297

378 400

468 499

558 604

645 705

T = 21.1 °C

B = 739.5 mm Hg
Table 1C

Alnor Velometer

Series 6000-P

Pitot probe-1250 Scale

Indicated Air Speed,

fpm

True Air Speed

fpm

100

140

190

280

380

102

153

198

297

401

470

560

645

498

605

706

T = 21.8 °C

B = 740.1 mm Hg

Table ID

Alnor Velometer

Series 6000-P

Pitot probe-1250 Scale

Indicated Air Speed,

fpm

True Air Speed,

fpm

100

140

188

285

378

102

153

198

297

401

468

560

645

498

603

704

T = 21.8 °C

B = 740.1 mm Hg
Table IE

Alnor Velometer

Series 6000-P

Pitot probe-1250 Scale

Indicated Air Speed, True Air Speed,

fpm fpm

100 102

140 153

192 198

285 297

378 402

470 497

560 602

648 709

T = 21.8 °C

B = 741.0 mm Hg
Table 2A

Alnor Velometer

Series 6000-P

Pitot probe-2500 Scale

Indicated Air Speed,

f pm

True Air Speed,

fpm

75

125

190

300

410

103

149

201

300

399

540

645

760

502

604

705

T - 21.1 °C

B = 749.2 mm Hg

Table 2B

Alnor Velometer

Series 6000-P

Pitot probe-2500 Scale

Indicated Air Speed, True Air Speed

fpm fpm

75 103

130 149

190 200

295 299

420 399

540 503

655 604

755 707

= 21.1 °C

= 749.2 mm Hg

T

B
Table 2C • Alnor Velometer

Series 6000-P

Pitot probe-2500 Scale

Indicated Air Speed, True Air Speed,

fpm fpm

80 103

130 149

195 200

300 300

435 399

540 503

650 606

755 706

T = 21.1 °C

B = 749.3 mm Hg

Table 2D

Alnor Velometer

Series 6000-P

Pitot probe-2500 Scale

Indicated Air Speed, True Air Speed,

fpm fpm

80 103

135 149

185 200

305 300

425 399

540 503

645 605

750 704

= 21.1 °C

= 749.3 mm Hg

T

B
Table 2E

Alnor Velometer

Series 6000-P

Pitot probe-2500 Scale

Indicated Air Speed, True Air Speed

fpm fpm

75 103

125 149

190 200

300 300

420 398

540 503

650 605

755 705

T = 21.1 °C

B = 749.3 mm Hg
Table 3A

Alnor Velometer

Series 6000-P

Diffuser probe-2500 Scale

Indicated Air Speed,

fpm

True Air Speed,

fpm

75

145

230

395

540

101

148

201

301

401

675

820

940

501

602

701

T = 21.1 °C

B = 747.8 mm Hg

Table 3B

Alnor Velometer

Series 6000-P

Diffuser probe-2500 Scale

Indicated Air Speed, True Air Speed

fpm fpm

75 101

145 149

240 200

395 301

545 401

680 503

815 602

940 698

9

= 21.1 °C = 747.8 mm Hg

T

B
Table 3C

Alnor Velometer

Series 6000-P

Diffuser probe-2500 Scale

Indicated Air Speed,

fpm

True Air Speed,

fpm

80

145

245

400

540

101

149

200

301

401

680

820

940

T = 21.1 °C

B = 747 . 5 mm Hg

Table 3D

Alnor Velometer

Series 6000-P

Diffuser probe-2500 Scale

499

601

699

Indicated Air Speed,

fpm

True Air Speed,

fpm

90

150

240

395

545

101

147

201

301

400

675

825

945

T = 21.1 °C

B = 747 . 5 mm Hg

501

600

698

T

B
Table 3E

Alnor Velometer

Series 6000-P

Diffuser probe-2500 Scale

Indicated Air Speed, True Air Speed,

fpm fpm

90 101

150 148

245 200

395 301

540 400

680 500

815 599

940 698

T = 21.1 °C

B = 747.3 mm Hg
Table 4A

Alnor Velometer

Series 6000-P

Diffuser probe-1250 Scale

Indicated Air Speed, True Air Speed,

fpm fpm

135 101

195 149

280 199

395 300

510 401

620 498

735 601

840 698

T = 21.1 °C

B = 746.0 mm Hg

Table 4B

Alnor Velometer

Series 6000-P

Diffuser probe-1250 Scale

Indicated Air Speed, True Air Speed,

fpm fpm

130 101

200 148

278 198

398 299

515 399

620 498

738 599

840 699

= 21.1 °C

= 746.0 mm Hg

T

B
Table 4C

Alnor Veloraeter

Series 6000-P

Diffuser probe-1250 Scale

Indicated Air Speed,

fpm

True Air Speed,

fpm

130

200

278

400

515

102

149

199

300

401

620

740

840

T = 21.1 °C

B = 745.4 mm Hg

Table 4D

Alnor Velometer

Series 6000-P

Diffuser probe-1250 Scale

500

602

697

Indicated Air Speed,

fpm

True Air Speed,

fpm

135

200

278

398

515

101

149

200

301

402

618

738

843

T = 21.1 °C

B = 745.4 mm Hg

501

601

701

T

B
Table 4E

Alnor Velometer

Series 6000-P

Diffuser probe-1250 Scale

Indicated Air Speed, True Air Speed,

fpm fpra

138 101

200 148

275 199

395 301

518 401

620 499

738 603

840 696

= 20.6 °C

= 744 . 3 mm Hg

T

B
Table 5A

Alnor Velometer

Series 6000-P

Low Velocity probe

Indicated Air Speed,

fpm

True Air Speed,

fpm

33

47

68

93

145

43.0

56.5

77.6

102

150

207 199

297 271

T = 20.6 °C

B = 742.5 mm Hg

Table 5B

Alnor Velometer

Series 6000-P

Low Velocity probe

Indicated Air Speed, True Air Speed

fpm fpm

33 42.9

45 56.5

66 77.4

94 101

145 150

207 199

296 272

= 20.6 °C = 742.5 mm Hg

T

B
Table 5C

Alnor Velometer

Series 6000-P

Low Velocity probe

Indicated Air Speed,

fpm

True Air Speed,

fpm

32

46

67

92

146

42.6

56.1

77.6

101

149

207

295

199

270

T = 20.0 °C

B = 742.0 mm Hg

Table 5D

Alnor Velometer

Series 6000-P

Low Velocity probe

Indicated Air Speed,

fpm

True Air Speed,

fpm

34

45

68

93

144

42.9

55.8

77.3

101

149

208

295

198

271

T = 20.0 °C

B = 742.0 mm Hg

i
Table 5E

Alnor Velometer

Series 6000-P

Low Velocity probe

Indicated Air Speed,

fpm

True Air Speed,

fpm

33

48

68

94

144

42.3

56.9

77.6

102

149

207 199

296 272

T = 20.0 °C

B = 740.3 mm Hg
FIGURE 1 THE ANEMOMETER WITH PITOT PROBE MOUNTED IN

TUNNEL SHOWING METHOD OF SUPPORT.
FIGURE 2 . THE ANEMOMETER WITH DIFFUSER PROBE MOUNTED

IN TUNNEL SHOWING METHOD OF SUPPORT.
FIGURE 3. THE ANEMOMETER WITH LOW-VELOCITY PROBE MOUNTED

IN TUNNEL SHOWING METHOD OF SUPPORT.

i
o 00 <N o o CTi CT\ <T\ on ON

1—

1

O o O O O

I 8 S3 I S3

DISTANCE

UPSTREAM

FROM

ANEMOMETER

(cm)
t

u.

1

(fpm)

0 100 200 300 400 500 600 '00

U (fpm)

FIGURE 5. INDICATED VERSUS TRUE VELOCITY FOR PITOT PROBE, LOW RANGE.
FIGURE 6. INDICATED VERSUS TRUE VELOCITY FOR PITOT PROBE, HIGH

RANGE.
U (fpm)

FIGURE 7. INDICATED VERSUS TRUE VELOCITY FOR DIFFUSER PROBE, LOW

RANGE.
1000 4- 4.

u.

1

900

800

700

600 ••

(fpm) 500

400

300

200

100 ..

t I 4 4 4 4 *

0 100 200 300 400 500 600 700 800 900 100

U (fpm)

FIGURE 8. INDICATED VERSUS TRUE VELOCITY FOR DIFFUSER PROBE,

HIGH RANGE.
300

250

200

150

100

50

0

50 100 150 200 250

U (fpm)

’IGURE 9. INDICATED VERSUS TRUE VELOCITY FOR LOW VELOCITY PROBE

.

300

Ht O o\ cx3r^^OLn<rco<NiH

S

Cu

4-4

J

100

200

300

400

500

600

700

U

(f

pm)

.

a

and

a

IN

TERMS

OF

TRUE

VELOCITY

FOR

PITOT

PROBE,

HIGH

RANGE.

R/2

NOTED.
m

100

200

300

400

500

600

700

U

(fpm)

FIGURE

12.a

ANDa

in

TERMS

OF

TRUE

VELOCITY

FOR

DIFFUSER

PROBE,

LOW

RANGE.

R/2

NOTED.
+ < - —

cs

D

D

s

P.

4-1

100

200

300

400

500

600

700

U

(f

pm)

o

AND

a

IN

TERMS

OF

TRUE

VELOCITY

FOR

DIFFUSER

PROBE,

HIGH

RANGE.

R/2

NOTED.
ooo

MOo

*3- CM o

o o

CM

CC u

o

o

'

100

_

200

300

U

(fpm)

FIGURE

14.

a

AND

o

IN

TERMS

OF

TRUE

VELOCITY

FOR

LOW

VELOCITY

PROBE.

R/2

NOTED.
+

R/2U

FIGURE

J5.a

AND

<>(.

AS

PERCENT

OF

GROUP

MEAN

VELOCITY

T?OR

PITOT

PROBE,

LOW

RANGE.

R/2 U

NOTED.

CJ. D

CM 13

D

ps5

-

HJO

200

300

-

(fpm)

400

500

600

700

a

and

O

c

AS

PERCENT

OF

GROUP

MEAN

VELOCITY

FOR

DIFFUSER

PROBE,

LOW

RANGE.

R/2U

NOTED.
00 LO cn 04 o

o

to Is

CN

pi

5^ IS

to

0

100

200

300

—

400

500

600

700

FIGURE

18.

G

and

O

c

AS

PERCENT

OF

GROUP

MEAN

VELOCITY

FOR

DIFFUSER

PROBE,

HIGH

RANGE.

R/2U

NOTED.
0°|G>

CM

G

Pi

S'?

J

100

U

(f

pm)

200

300

O

AND

a

c

AS

PERCENT

OFCROUP

MEAN

VELOCITY

FOR

LOW

VELOCITY

PROBE.

R/2U

NOTED.
•H

I

l=>

e

QU-l
FIGURE

21.

DEVIATION

OF

INDICATED

VELOCITY

FROM

TRUE

VELOCITY

FOR

PITOT

PROBE,

HIGH

RANGE.
(fpm)

o 0

CM

1 o o

I I 0

00

1

o

01—

1

0

i-H

1

0

<r

rM

1

H

I

e

a.

FIGURE

22.

DEVIATION

OF

INDICATED

VELOCITY

FROM

TRUE

VELOCITY

FOR

DIFFUSER

PROBE,

LOW

RANGE.
z

<

OS

as

aas

asan

<

>

£3

I £3

E

CL

4-1
•H

E=> E&

I u-i P

FIGURE

24.

DEVIATION

OF

INDICATED

VELOCITY

FROM

TRUE

VELOCITY

FOR

LOW

VELOCITY

PROBE.

U

(fpm)

FIGURE

26.

PERCENT

DEVIATION

OF

INDICATED

FROM

TRUE

VELOCITY

FOR

PITOT

PROBE,

HIGH

RANGE.
(f

pm)

•H PI P P S'? 1

PERCENT

DEVI

AT

ION

OK

INDICATED

FROM

TRUE

VELOCITY

FOR

DIFFUSER

PROBE,

LOW

RANGE.
I III

•H

E3

I P 6-5

U

(fpra)

FIGURE

28.

PERCENT

DEVIATION

OF

INDICATED

FROM

TRUE

VELOCITY

FOR

DIFFUSER

PROBE,

HIGH

RANGE.
FI

CURE

2

(J.

PERCENT

DEVIATION

OF

INDICATED

FROM

TRUE

VELOCITY

FOR

LOW

VELOCITY

PROBE.


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