NBSIR 79-1759 R

Low Velocity Performance of

Anemometers

L P. Purtell

National Bureau of Standards

Fluid Engineering Division

Washington, D C. 20234

May 1979

Final Report on

Contract No. HOI 661 98

Evaluation of the Behavior of Mine Anemometers in the NBS Low

Velocity Calibration Facility

Prepared for United States Department of the Interior

Bureau of Mines

NBS-U4A (REV. 9-76

)

1 USCOMM-DC
- 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, 1976, and November 30, 1978. This

report was submitted by the author May 1979.

ic 0

2
NBSIR 79-1759

LOW VELOCITY PERFORMANCE OF

ANEMOMETERS

L. P. Purtell

Fluid Engineering Division

Center for Mechanical Engineering

and Process Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D C. 20234

May 1979

Final Report

Prepared for United States Department of the Interior

Bureau of Mines

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

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director
1
NOMENCLATURE

U velocity measured by laser velocimeter standard

U. velocity indicated by anemometer under test

1

f frequency output from (vortex-shedding) anemometer under

test (Hz)

I current output from (heated foil) anemometer under test (yA)

line segments fitted to (U,U^) , (U,f)> or (U,I) data

U group mean true velocity

U_^ group mean indicated velocity

f group mean indicated frequency

I group mean indicated current

a. standard deviation of U. data about U

.

x x if

a c standard deviation of f data about U._

f it

standard deviation of I data about U

.

I if

a a., o c , or a_ divided by dU.^/dU

i f I if

a a corrected for known variance in laser velocimeter measurements

c

R. resolution of the instrument under test

1

R resolution expressed as true velocity

3
LOW VELOCITY PERFORMANCE OF ANEMOMETERS

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 2.5 meters per second, undertook the development of a lowvelocity calibration facility for wind speed measuring instruments

which would provide a capability down to 0.05 meters per second

(approximately 10 feet per minute) 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 stateof-the-art and to provide the information needed as to the reliability

and performance of instrumentation for such measurement. Thus various

types of instruments for low velocity air measurement have undergone

testing at MBS. This report summarizes the results and presents

analyses of the instruments' performance.

Performance is measured in terms of a comparison between indicated

and true air speed, the variation in repeated measurements, and the

minimum operating air speed. Since the indicated air speed may be

easily corrected using a chart, for instance, to find the true air

speed, the latter two measurements of performance are of primary

interest. Thus a detailed handling of random error is presented

including the effect of instrument resolution where necessary.

2. THE FACILITY

The data reported here were measured in the Low Velocity Airflow Facility [1] at the National Bureau of Standards. The facility

consists primarily of a low velocity wind tunnel and a laser velocimeter velocity standard. The wind tunnel (Figure 1) is an open

return type with the fan pulling the air through the tunnel.

The test section, 6.1 m in length and nominally 0.91 m by 0.91 m

in cross-section, is constructed of acrylic panels mounted in a steel

frame. The test section is supported from above by I-beams to allow

the laser velocimeter traversing gear, mounted on rails on the floor

of the room parallel to the test section, to be positioned at any

location along the length of the test section.

The performance of the wind tunnel in terms of steadiness,

flatness of mean velocity profiles, and turbulence level is extremely

satisfactory. No drift in air velocity during a test was detected.

The mean velocity profiles outside of the wall boundary layers are flat to within 0.5% even as close as 1 meter from the entrance to

the test section. The residual turbulence intensity is less than

0.05%.

A laser velocimeter is used as the velocity standard. It is

linear with velocity from first principles and does not suffer a

4
severe loss of resolution at very low velocities as does, for

instance, the Pitot-static tube. Furthermore, it is nonintrusive

and has good spatial resolution. Adequate sensitivity is obtained

in the facility without the artificial 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.

3 . THE INSTRUMENTS

Instrument A — Bronze bearing vane anemometer.

All of the vane anemometers tested have flat vanes without

camber or twist as opposed to helicoidal types. All but one (instrument E below) are entirely mechanical and require only a timer (stopwatch) for operation.

Instrument A is a commercially available instrument (Davis

Instrument Manufacturing Company, Incorporated, 4- Inch Low Speed

Anemometer, S/N 22889). It was supplied for test by the U. S. Mining Enforcement and Safety Administration (MESA) at the request

of the U. S. Bureau of Mines. The housing is 4 inches (10.2 cm)

in diameter and 1-3/4 inches (4.4 cm) deep (Figure 2). Thin metal

vanes without camber or twist mounted on arms drive a rotor linked

to a dial indicator by a gear train. The bearings in this particular

instrument are standard bronze bearings (as opposed to ball bearings)

.

One revolution on the dial represents an indicated passage of 100

feet of air through the instrument. Thus an external timer (not a part of the anemometer) is required to complete a measurement of

velocity (an average velocity for the duration of the measurement)

.

Instrument B — Ball bearing vane anemometer.

This anemometer is a commercially available instrument (Davis

Instrument Manufacturing Company, Incorporated, 4-Inch Low Speed

Anemometer, S/N 24323 B) . It was supplied for test by the U. S. Mining Enforcement and Safety Administration (MESA) at the request

of the U. S. Bureau of Mines. As may be seen in Figure 3, it is

identical to instrument A except that the bearings are ball bearings

instead of bronze bearings.

Instrument C — Jewel bearing vane anemometer.

This anemometer is a commercially available instrument (Sybron/

Taylor Corporation, 4-Inch Anemometer, S/N H873) . It was supplied

for test by the U. S. Mining Enforcement and Safety Administration

(MESA) at the request of the U. S. Bureau of Mines. It is very

i These particular instruments were selected as being representative

of the type of anemometer and their selection does not represent an endorsement

.

5
similar in appearance (Figure 4) to instruments A and B though the

dimensions of the hub and shroud are slightly different. The

bearings, however, are jewel instead of bronze or ball bearing.

Instrument D — High speed vane anemometer.

This anemometer is a commercially available instrument (Davis

Instrument Manufacturing Company, Incorporated, 4-Inch High Speed

Anemometer, S/N 31125B) . It was supplied for test by the U. S.

Mining Enforcement and Safety Administration (MESA) at the request

of the U. S. Bureau of Mines. This anemometer (Figure 5) is

dimensionally identical to instrument B, including ball bearings,

but has four vanes instead of eight, thus permitting operation at

higher air speeds.

Instrument E — Magnetic pick-up vane anemometer.

This anemometer is a commercially available instrument (Abbirko

Instruments, Limited, Flowmaster, S/N 6184). 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's vane

housing is approximately 2.75 inches (7.0 cm) in diameter (see

Figure 6) with an attached block for the magnetic pick-up, or proximity transducer, and a handle projecting down from the block.

The magnetic pick-up detects the passage of the metal vanes, and

the resulting electrical signal is converted to a deflection of a meter connected to the probe by a cable. The meter was located

outside the tunnel during the tests and was oriented horizontally.

Three ranges of operation are selectable: low - 0 to 300 fpm,

medium - 0 to 1000 fpm, and high - 0 to 3000 fpm. The anemometer

requires a 9 volt battery for operation.

Instrument F — Full size impact-deflection anemometer.

This type of anemometer operates from the dynamic pressure of

the air stream. This pressure is converted to a deflection of a dial

indicator by impacting a small vane linked to the meter. The

operation is thus entirely mechanical.

Instrument F is a commercially available instrument (Alnor

Instrument Company, Velometer, Series 6000-P) . 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 (Figure

7) consists of a main body meter (approximately 15 x 17 x 6 cm)

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

of a cylinder 0.5 inches (1.27 cm) in diameter and 13 inches (33 cm)

long which mounts in a range selector unit connected to the main body

by hoses. 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,

6
but were not tested herein.

The diffuser probe (Figure 8) 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.

The low velocity probe (Figure 9) 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.

Instrument G — Compact impact-defection anemometer.

This anemometer is a commercially available instrument (Alnor

Instrument Company, Velometer Jr., Type 8100). 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 is approximately

8.2 x 10.2 x 3.8 cm in size (see Figure 10) and contains entrance and

exit ports for the air on the upstream and downstream surfaces, respectively.

The entrance port is adjustable (two sizes) providing two ranges of

velocity measurement, 50 to 200 fpm and 100 to 800 fpm. The instrument

is a one piece, self-contained unit.

Instruments H and I — Vortex-Shedding Anemometers.

This type of instrument measures velocity by detecting the frequency

of a vortex street shed from a bluff, two-dimensional object such as a cylinder. This frequency will be well-defined if the shedding body is

properly matched to the air speed.

These anemometers (two units, serial numbers 49 and 48, respectively,

are commercially available instruments (J-TEC Associates, Incorporated,

VA-216 Air Draft Sensor) 1 supplied for test by the U. S. Bureau of

Mines. The instruments are approximately 30 x 10 x 14 cm in size

(see Figure 11) and include probe heads and the necessary electronics

for operation. The probe head consists of a rod approximately 6.4 mm

in diameter and 35 mm in length supported at the ends and oriented normal

to the air stream. An ultrasonic transmitter and receiver pair located

downstream of the cylinder detect the vortex street shed by the cylinder

as an amplitude modulation of the ultrasonic signal. This modulation

is converted by the electronics section to a pulse train (approximately

a square wave signal) as an output. A frequency-to-voltage converter

section also provides an analog output. Since the frequency of shedding

of a vortex street is roughly proportional to velocity, the output

signals can be used to measure the air velocity. A separate power

supply is necessary to operate the instrument.

Instrument J — Heated foil anemometer.

This anemometer is a prototype instrument (Thermogage, Inc.

,

7
Air Velocity Meter) supplied for test by the U. S. Bureau of Mines.

It consists of a tube approximately 9.5 ram in diameter and 10.2 cm

in length aligned with the flow, and a 15.9 mm diameter handle attached

normal to the tube midway along its length (see Figure 12). A part of

the wall of the tube is composed of a heat-conducting foil which has an electrically heated spot flanked upstream and downstream by temperature

sensors. As air passes through the tube, the upstream sensor experiences

a lower temperature than the downstream sensor, and this difference,

converted to an electrical signal, is related to velocity. The instrument

thus consists of this thermal transducer and an electronics module containing

a line-voltage operated power supply, the necessary circuitry, and a micro-ammeter

4. THE TESTS

4.1 General Description

Many types of tests can be performed on various aspects of an instrument’s performance, such as its response to turbulent flow,

shock and vibration, dirt, moisture, or orientation to velocity and

gravity vectors, but the results of such tests require comparison with

a base level of performance. This base level should be obtained under

conditions closely approximating the ideal environment, which, in the case of anemometers is a steady, uniform flow field of large dimensions.

The Low Velocity Airflow Facility has been found to provide a good

approximation to these conditions for the instruments reported on here.

The performance is measured in terms of the mean error, the random

error, and minimum operating air speed. The mean error, for the 'purposes

of this report, is defined simply to be the mean difference between

the air speed indicated by the anemometer under test and the air speed

indicated by the velocity standard. Random error is defined as usual

in terms of a root-mean-square deviation of the indicated air speed from

an appropriate mean value (see section 5 for more details) . To permit

evaluation of these characteristics, multiple calibration tests and

minimum operating speed determinations were performed.

4.2 Calibration tests

These tests consisted of measuring the response of the anemometer

undergoing testing to an air flow of a speed measured by the laser

velocimeter velocity standard. (See tables A-l through J-5) . Each

instrument was tested at a number of air speeds over the range of

operation below about 4 m/s. Five such tests were conducted for each

instrument with an attempt made to repeat the air speeds for each test.

(The effects of not exactly repeating the air speeds are discussed in the

analysis of section 5). The particular test set-up for the calibrations

varied somewhat from instrument to instrument, but in general consisted

of mounting the anemometer on or near the centerline of the test-section,

1 m from its upstream end, locating the laser velocimeter probe volume

at a position where disturbance of the flow due to the presence of the

anemometer is negligible, and measuring the air speed with both the

8
anemometer under test and the laser velocimeter standard. The details

which varied from instrument to instrument are described in the following

paragraphs

.

Four of the vane anemometers, A, B, C, and D, are so similar in

dimension and function that the tests were nearly identical for them.

The location of the probe volume (30 cm upstream of the anemometer) was

the same for each and was determined from a series of velocity measurements

upstream of instrument A. These are presented in Figure 13 as the ratio

of the local velocity to the frees tream velocity. These measurements

were performed at two freestream speeds, 3.6 and 0.36 m/s to verify

independence of freestream speed as predicted by potential flow theory.

With no anemometer in the tunnel, variation in velocity along the centerline

is imperceptible over the distance traversed.

The same four anemometers. A, B, C, and D, also require a timer to

determine the indicated airspeed. This was computed from initial and final

readings of the dial and of the associated time interval (around two

minutes) . The anemometer runs continuously in the tunnel since it

cannot be accessed while the tunnel is in operation without disturbing

the flow. Thus the readings of the anemometer were performed with the

anemometer in operation. The laser velocimeter measurement of the

air velocity was performed during the time interval for reading the vane anemometer.

The remaining vane anemometer, instrument E, has an electronic

read-out, thus not requiring a separate time measurement. It is

smaller in dimension than A through D and will disturb the air-flow

less. Consequently the probe volume could be located as for instruments

A through D. As with the others, the laser velocimeter measurement of

the air velocity was performed during the time interval for reading the vane anemometer.

The full size impact deflection anemometer, instrument F, has

three velocity probes which were tested on all ranges. The Pitot probe

and diffuser probes are essentially slender (1.27 cm diameter) cylinders

presenting little disturbance to the flow. Thus they were tested with

the probe volume located 30 cm upstream of the probe as with the vane

anemometers. The meter body and hoses were located downstream of the

probes. The low velocity probe, however, attaches directly to the meter

body rather than by hoses, thus requiring the meter body and probe

to be placed together at the calibration position. Thus the velocity

upstream of this combination was measured to again find a location for

the probe volume. However, 30 cm upstream was found to be quite

sufficient (Figure 14)

.

The velocity upstream of the compact impact-deflection anemometer,

instrument G, was also measured to find a location for the probe volume,

and again 30 cm was found to be sufficient.

9
The vortex-shedding anemometers, instruments H and I, are larger than

the others and disturb the flow proportionately more. However, it was

found that by placing the measuring head on the centerline (thus with the

bulk of the instrument off the centerline) that the laser velocimeter

probe volume could be located 35 cm upstream of the instruments . Since

the outputs of H and I are an analog voltage and a pulse train, separate

instrumentation consisting of a digital volt meter and a frequency counter

were required for the tests. These measurements were recorded during

the time interval required for measurement by the laser velocimeter

standard.

The remaining instrument, the heated foil anemometer, instrument J,

has a very small probe head and was thus tested with the probe volume

again at 30 cm upstream. The output is an analog meter reading in

microamps

4.3 Minimum Operating Speed

Determination of the minimum air speed at which operation of an instrument is possible varies with the type of instrument under test.

The instruments may be separated into two categories for this purpose:

instruments that entirely cease to function below some speed, and

instruments that lose sufficient resolution in their output (or read

zero) below some speed.

The vane anemometers, A through E, all fit in the first category,

but here two minimum operating speeds may be defined, a starting speed,

the speed at which the instrument starts from rest as the air speed is

slowly increased, and a stopping speed, the speed at which the anemometer

ceases to turn as the air speed is slowly decreased.

To determine the starting speeds of the instruments, the velocity

in the tunnel was increased from below the starting speed at a smooth

acceleration of approximately 0.15 m/s/min until movement of the vanes

could be detected by eye. At that moment the air velocity would be

fixed and the laser velocimeter measurements initiated. If the anemometer

continued rotating for at least thirty seconds and did not decelerate,

the measurement of velocity by the laser velocimeter was recorded as the

starting speed.

Because of the anemometer's angular momentum, stopping speed is

more difficult to determine than starting speed. Some preliminary runs indicated that a two minute interval between reductions in air velocity

of approximately 1 cm/s was sufficient for the anemometer to come to

rest if the stopping speed had been reached.

The only other instruments having minimum speeds of functioning

are the vortex-shedding anemometers, instruments H and I. As the air

speed is reduced the depth of modulation of the ultrasonic signal is

reduced until at some speed it can no longer be detected by the instruments.

10
Since neither friction nor angular momentum is involved, as opposed to the vane anemometers, the minimum operating speed was easily determined by

simply observing the pulse train from the instruments as the air speed was

slowly reduced. When the pulses disappeared (which occurred rather

abruptly) the air speed was recorded as the minimum operating speed.

The other instruments, the impact pressure anemometers, F and G, and

the heated foil anemometer, J, all fit in the second category of instruments

which lose sufficient resolution below some speed. This minimum operating

speed is defined here to be that at which the anemometer under test

indicates a speed of one-half the lowest marked division on the dial above

zero. This was chosen because at that indicated speed the resolution is

at least as large as the reading.

5. RESULTS AND DISCUSSION

5.1 Methods of data analysis

As may be observed in Figures 16 through 32, the data for the

calibration curves are in groups because of attempts to repeat the true

air speeds from run to run. The mean calibration data are defined to be

the pairs of values consisting of the mean true velocity for a group and

the mean indicated velocity (or frequency, etc.) of that group. Plots

of these pairs (connected by solid lines in Figures 16 through 32)

,

give an indication of linearity of the instrument's response and serve

in determining the random error of that response. Furthermore, the mean

data may be used to define calibration curves for correcting an indicated

reading in the field. Figures 33 through 59 (odd numbered) are especially

valuable in this respect.

Random error is frequently defined as the standard deviation (about

the mean) of repeated measurements. This is only useful, however, if the

true or reference value is fixed or has negligible variation from

measurement to measurement. Precise repetition of wind tunnel speeds,

though, is extremely difficult at the low speeds required for these tests.

The random error here, then is defined in terms of the root-mean-square

deviation of the data in a group from an appropriate curve through that

group. This _is illustrated in Figure 15 where U is the group mean true

velocity and U. is the group mean indicated velocity. An ideal calibration

curve, U.(U), is approximated within the group by a straight line segment,

U.

f

, passing through (U,U.). The root-mean-square deviation, curve,

U^XU) , is approximated_wi.^hin the group by a straight line segment,

Uif, passing through (U,U.). The root-mean-square deviation, of the

data, (U ,U. ) from U‘.(ut is thus approximated by the root-mean-square

deviation from the line segment, U More specifically:

a

2 * ^ l [U. - U..(U. )]

2 i N

L

, ir if lr r=l

The slope of the line segment, U is computed as the average of the _

slopes of line segments connecting the (U,U.) of interest with the (U,U.)'s

of the neighboring group (s).

11
The standard deviation, a., is a measure of the scatter in the data

in terms of indicated air speecl (or frequency, etc. , depending on the

measurement). To compare instruments, however, this must be converted

to an equivalent scatter in true air speed. An approach consistent with

the above approximations for a. is to divide a. by the local slope of

U.-, namely (dlL^/dU). The result, cr, is now taken to be a measure of

tte random error of the instrument in terms of true velocity, subject to

the corrections and limitations discussed below.

Computing o

from measurements by an instrument having a scale with

a resolution, R., much smaller than a. is an accepted procedure for

determining repeatability of the instrument. However, if the resolution is

large (poor) compared to a. (where a. is presumed known by some means independent of the scale being considered, say by a second scale with

better resolution) , the indicated a may be much smaller than it should

be. For a Gaussian distribution of errors it is assumed that o. may be

adequately computed if the resolution is at most approximately twice cr_^.

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

,

were converted to equivalent values, in terms of true velocity by

dividing by the slope (dU /dU). These latter values, divided by two,

were then included in the figures where applicable in units of velocity

or as percentage of U. As will be seen, R/2 does indeed exceed a for

several of the instruments. Thus these particular 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 random

error may exceed the quality of its resolution.

The above analysis presumes that the contribution to the random

errors from the laser velocimeter is negligible, and indeed this is

true for most of the tests. The random uncertainty of the laser

velocimeter (random error) may be estimated from repeated measurements at a particular fan setting, thus also including any un- steadiness in the air speed. The value of this uncertainty was reduced as improvements were made to the laser system and varied

from 0.005U for instruments A and B to 0.002U for instrument C

to 0.001U for all the others. A corrected standard deviation for

the tested instruments, ct^, may thus be computed from, for instance,

a

2 = a2 - (0.001U) 2 c for any given U. Values of a are included in the figures where

they differ perceptibly from 8he values of a. Since ± 2 a is close

to the 95 percent confidence interval for one measurement, curves

of ± 2 are also included in the figures of IL against U.

5.2 Calibration Data

The calibration data is presented in three forms for those

instruments (A through G) that read directly in velocity: indicated

versus true velocity, the deviation of indicated from true velocity

against indicated velocity, and the percent deviation against true

12
velocity (Figures 16 through 60). Instruments H, I, and J have

only plots of indicated output (frequency for H and I; current

for J) against true velocity. Figures 30, 31, and 32. The primary

function of the figures showing indicated velocity or output against

true velocity is to illustrate the overall character of the response

and the 95% confidence intervals. The other types of figures detail

the features of most interest: the linearity, the range of scatter,

and the deviation of indicated from the true velocity.

Vane anemometers A, B, and D are nearly identical in dimension

and also have very similar calibration curves (see Figures 16, 18,

19, 33 through 36, 39, and 40). The rapid rise in the curve of Figure

33 as the velocity is reduced below 100 feet per minute (0.5 m/s)

is almost certainly due to the appearance of friction effects since

this instrument. A, has bronze bearings rather than ball bearings

as do instruments B and D.

Instrument C, though a vane anemometer similar in appearance

to A, B, and D, does differ somewhat from them, especially in the

size and shape of the hub. This may explain the somewhat different

character of the calibration data as presented in Figures 18, 37,

and 38, though the instruments A, B, C, and D really all have quite

similar calibration characteristics.

The magnetic pick-up transducer and associated electronics of

instrument E may be the fundamental cause of the somewhat different

character of its calibration data (figures 20, 21, 22, and 41 through

46) as compared to A through D. This is evidenced by the change

in the data between ranges on the instrument (e.g.. Figures 41 and

43)

.

This cannot be caused by the dynamics of the vane since

mechanically and aerodynamically the instrument is unchanged when

compared at the same speed but on different ranges. The overall

character of the calibrations though is not significantly different

from those of A through D.

The characteristics of the calibration data for the impactdeflection type instruments, F and G, are determined by the aero- dynamic characteristics of the probes and flow passages in the

instruments as well as the meter characteristics. The different

responses in the data of Figures 23 through 29, and 47 through

60 show the effect of various probes and ranges. The only major

conclusion to be drawn at this point is that at the lower velocities

it is usually very important because of large errors to use a good

calibration correction method (chart or table, etc.) when making a measurement. This is true for all the instruments, A through G.

There is little to comment upon concerning the calibration

curves for the vortex-shedding and heated film anemometers (H, I,

and J) since the output is not "velocity." Both the principle of

vortex street frequency-to-velocity relationship and the temperatureto-velocity relationship have long been known. These particular

instruments have utilized these principles so that sufficient

13
sensitivity to velocity changes is produced. Both the near linearity of the vortex frequency with velocity and the usual non- linearity of the heat transfer to velocity are apparent in the

data (Figures 30, 31, and 32).

5 . 3 Random Error

The random error, defined in Section 5.1, is presented in

essentially two forms: in units of velocity, and as percent of group

mean true velocity. The exceptions are instruments H, I, and J which

do not read out in velocity and thus also have plots of random

error in units of their read-out (frequency or current) . As was discussed in Section 5.1, the measure of random error, a, is in

terms £f true velocity which was produced by dividing a . by

(dU./dU). The random error for the instruments not havxng direct

reac[-out in velocity was also expressed in this manner by dividing

the random error in terms of the _readout (f_ or I) by the group mean

slope of the calibration curve (df/dU or dl/dU).

The rather small sample size, five runs, causes a sizeable

uncertainty in any one value of the random error. This is ameliorated

somewhat though by the many values of velocity at which the random

error was computed, thus permitting a smoothing of the data and

effective reduction in the uncertainty. The data as presented,

however, have not been smoothed but are the values computed according

to the procedures presented in Section 5.1.

The data for vane anemometers A, B, C, and D (Figures 61 and

62 for A, 63 and 64 for B, 65 and 66_for C,_and 67 and 68 for D)

all show the same trends of a and a/U with U differing only in

magnitude. The quite different character of the random error for

instrument E, the only one with a magnetic pick-up transducer.

Figures 69 and 74, is most likely associated with the effects of

resolution as discussed in Section 5.1. As noted in the figures,

the computed a is frequently less than the value R/2. The other

vane anemometers did not have random errors the same order as the

resolution. For evaluation, as noted in Section 5.1, instrument

E should perhaps have a replaced by R/2 for those values of a less

than R/2.

The impact-deflection type anemometers, instruments F and G,

likewise have random errors exceeded by the values R/2 at some air

speeds (Figures 75 through 88). None of E, F, or G, however, show

any adverse or highly unusual characteristics in the trends of the

random error with velocity.

The effect of resolution on the vortex-shedding anemometers,

instruments H and I, was eliminated by selecting instrumentation

for reading the frequency which had far better resolution than

required. This was possible in the laboratory because of the

unprocessed signals, a pulse train and a voltage, available from

14
the instruments under test. The only slightly unusual feature of

the results (Figures 89 through 96) was that for instrument H,

decreased. Since the instruments are nominally identical, no explanation is apparent for the (slight) variation.

The heated foil anemometer, instrument J, showed trends with

velocity similar to A through D, but had resolution almost perfectly

matched to the random error (Figures 97 through 100).

As discussed in Section 4.3, the minimum operating speed is

determined in different ways for different instruments. The vane anemometers and the vortex-shedding anemometers all have minimum

operating speeds determined by a complete ceasing of operation.

The others simply lose resolution below some air speed. The various

minimum operating speeds are summarized in Table K.

The difference in starting and stopping speeds for the vane

anemometers, A through E, is due to the difference in static and

dynamic friction factors for the bearings. Both speeds, though,

are lower for the instruments with the more friction-free bearings,

such as B and D. Instrument D, having fewer vanes than B, can operate at higher air speeds,. but this advantage is offset somewhat

by a decreased torque at lower speeds and thus a higher minimum

operating speed.

Since the minimum operating speed of the vortex-shedding

anemometers, instruments H and I, depends on the level of detection

of the ultrasonic modulation, the difference in the speeds for

these two instruments is probably due to slightly differing adjustments of the electronic detection circuits rather than a physical

or aerodynamic difference. As noted in Section 4.3, these instruments ceased operating rather abruptly as speed was reduced, thus

giving a well-defined minimum operating speed.

For the instruments having a minimum operating speed defined

by resolution, namely F, G, and J, the procedure for specifying

the speed is defined in Section 4.3, and the results are summarized

in Table K. The only comment on the results is that the resolution

as discussed in Section 4.3 is R. , the indicated resolution, whereas

the minimum operating speeds (for all the instruments) are true

speeds

.

Performance of ten anemometers of several different types has

been measured at low air speeds in a wind tunnel which provides a steady air flow of low turbulence. Multiple calibration runs on

/ f or a/U nearly constant with velocity. Instrument I,

.es which increased somewhat as velocity was

5.4 Minimum Operating Speed

6. SUMMARY

15
each instrument provided sufficient data for measuring performance

in terms of random error about the mean calibration curve as well

as the difference between the indicated and true speeds. Measurements were also performed of the minimum operating speeds of the

anemometers

The results are presented in both tabular and graphical form.

A detailed description is included of the tests, the results, and

the methods of analysis.

7 . REFERENCES

1. L. P. Purtell and P. S. Klebanoff, A Low Velocity Airflow Calibration

and Research Facility, MBS TN 989, 1979.

16
Table A1

Davis Vane Anemometer

Serial No . 22889

Indicated Air Speed,

fpm

True Air Speed,

fpm

730.0

730 . 0 208 . 0

479.0

67.8

6 79.0

687.0

208 . 0

458.0

94 .

2

21.0

26 . 4

28.8

6 3.6

6 3.0

76 . 2 75 . 0

72 . 0 94 . 2 89 .

4

T = 18.8 to 20.0 °C

B = 763.1 mm Hg

Table A2

Davis Vane Anemometer

Serial No . 22889

Indicated Air Speed, True Air Speed

fpm fpm

732 . 0 6 79.0

208.0 208 . 0 478 .

0

451.0

67. 2 91.8

37 .

8

73 . 2

37 . 2 65 . 4

28 . 8 64 .

8

60 .

0

90.0

6 3.6 91.2

T

B 20.1 to 21.0 °C763.1 mm H g
Table A3

Davis Vane Anemometer

Serial No. 22889

Indicated Air Speed,

f pm

True Air Speed,

fpm

732 .

211.0

482.0

70 . 2 39 . 3

690 . 0 207.0

458 . 0

94 .8

72 . 0

36 . 5 29 .

69 . 6

68 .

73 . 2 76 . 2 96 . 0

96 . 6

T = 21.0 °C

B = 755.0 mm Hg

Table A4

Davis Vane Anemometer

Serial No . 22889

Indicated Air Speed, True Air Speed

fpm fpm

735 . 0 687 .

210.0 214.0

481.0 460 .

69 .

94 .

39 . 1 75 . 6

44 .

76 . 8 45 . 3 75 .

70 . 8 96 . 6

70 . 8 96 .

T

B 21.6 °C764.0 mm Hg
Table A5

Davis Vane Anemometer

Serial No. 22889

Indicated Air Speed, True Air S

fpm fpm

710.0 688 .

0

208.0 215 . 479.0 458.0

67.8 95.4

25 .8 74.4

39.1 74.4

40.9 75.0

64.8 94 .

2

T = 21.6 °C

B = 764.0 mm Hg

Table B1

Davis Vane Anemometer

Serial No. 24323 B

Indicated Air Speed,

fpm

True Air Speed,

fpm

712

205

466

80.4

56.5

692

211

455

93.0

72.0

33.2

12.4

23.1

5.8

50.4

30.3

40.8

24.0

T = 20.9 to 21.0 °G

B = 745.7 mm Hg

Table B2

Davis Vane Anemometer

Serial No.' 24323 B

Indicated Air Speed,

fpm

True Air Speed,

fpm

752

218

491

85.6

60.8

724

224

484

99.3

73.1

37.1

14.3

24.8

6.8

151

51.1

29.6

40.6

23.0

158

= 21.7 to 21.9 0 - 744.8 mm Hg

T

B

C
Table B5

Davis Vane Anemometer

Serial No. 24323 B

Indicated Air Speed,

f pm

True Air Speed,

f pm

717

206

468

80.5

57.5

690

209

458

94.4

71.1

35.0

12.2

22.7

8.1

144

51.5

30.7

41.7

26.4

150

T = 21.3 °C

B = 747.1 mm Hg

Table B4

Davis Vane Anemometer

Serial No. 24323 B

Indicated Air Speed,

fpm

True Air Speed,

fpm

715

206

469

80.3

56.8

696

215

466

96.0

72.0

33.1

12.3

22.4

6 .

142

50.4

31.2

41.4

25.2

152

= 22.1 °C = 750.5 mm Hg

T

B
Table B5

Davis Vane Anemometer

Serial No. 24323 B

Indicated Air Speed,

fpm

True Air Speed,

fpm

718

207

471

78.8

56.0

682

212

461

97.2

70.8

33.8

13.6

26.9

11.5

114

50.4

32.2

43.4

29.5

153

T

B 22.5 °C

750.5 mm Hg

Table Cl

Taylor Vane Anemometer

Serial No. H873

Indicated Air Speed,

f pm

True Air Speed,

fpra

722

589

457

309

190

752

619

494

322

221

110

56.8

26.7

7.1

27.1

145

100

76.2

60.6

76.2

T = 22.8 °C

B = 751.2 mm Hg

Table C2

Taylor Vane Anemometer

Serial No. H873

Indicated Air Speed,

fpm

True Air Speed,

fpm

719

589

454

324

190

746

623

498

360

222

109

55.8

25.1

8.4

25.7

142

98.0

74.6

64.8

76.0

= 22.6 °C

= 753.5 mm Hg

T

B
Table C3

Taylor Vane Anemometer

Serial No. H873

Indicated Air Speed,

f pm

True Air Speed,

fpm

720

588

456

323

190

750

622

495

363

222

110

54.7

23.4

3.8

23.8

143

96.9

74.2

63.0

74.3

T = 22.6 °C

B = 753.1 mm Hg

Table C4

Taylor Vane Anemometer

Serial No. H873

Indicated Air Speed, True Air Speed

fpm fpm

723 752

590 622

458 499

324 361

190 221

110 142

54.9 97.1

22.4 73.6

23.0 72.4

T = 22.7 °C

B = 752.9 mm Hg
Table 05

Taylor Vane Anemometer

Serial No. H873

Indicated Air

fpm

Speed, True Air Speed,

fpm

721

588

457

323

190

742

624

496

360

220

109

54.5

20.0

8.5

20.8

141

96.4

72.6

65.5

72.5

9.8 66.1

T = 22.8 °C

B = 753.0 mm Hg

Table D1

Davis Vane Anemometer

Serial No. 31125B

Indicated Air Speed,

fpm

True Air Speed,

fpm

785

639

496

359

219

736

606

478

347

217

136.4

80.2

53.7

38.9

28.6

T =

B =

141.2

92.1

68.2

56.6

47.7

23.6 °C

753.8

mm Hg

Table D2

Davis Vane Anemometer

Serial No. 31125B

Indicated Air Speed,

fpm

786

640

497

358

219

137.3

81.8

56.1

41.8

26.4

T =

B =

True Air Speed,

fpm

741

608

477

348

218

141.7

93.1

70.2

58.8

47.3

23.8 °C

753.8 mm Hg
Table D3

Davis Vane Anemometer

Serial No. 31125B

Indicated Air

fpm

speed, True Air Speed,

fpm

786 738

641 608

498 477

358 347

218 216

135.5 139.5

81.1 91.5

53.7 68.0

38.9 55.7

24.5 43.4

T = 24.2 °C

B = 753.8 mm Hg

Indicated Air

fpm

Table D4

Davis Vane Anemometer

Serial No. 31125B

Speed, True Air Speed,

fpm

787 738

641 608

498 477

359 347

220 217

135.6 140.5

80.6 91.4

53.0 67.7

37.8 55.4

24.8 44 .

T = 24.6 °C

B = 753.8 mm Hg
Table D5

Davis Vane Anemometer

Serial No. 31125B

Indicated Air Speed,

fpm

True Air Speed,

fpm

786

641

498

357

219

740

608

476

347

217

134.6

81.0

52.6

38.3

27.1

140.0

91.4

67.1

55.3

46.3

o

Cmm HgT

B 24.7

753.2
I
Table El

Abbirko Flow-master

S/N 6184

Low Range

Indicated Air Speed, fpm True Air Speed, fpm

50 59.9

52 64 .

1

64 74.5

74 86.1

86 97.2

96 108.4

144 157

184 200

228 248

272 300

T = 20 . 8°C

B = 758.4 mm Hg

Table E2

Abbirko Flowmaster

S/N 6184

Low Range

Indicated Air Speed, fpm True Air Speed, fpm

50 59.6

54 64.0

64 74.0

76 86.4

86 97.1

98 108.8

144 157

186 200

228 250

274 299

T = 20. 8°C

B = 758.4 mm Hg
Table E3

Abbirko Flowmaster

S/N 6184

Low Range

Indicated Air Speed, fpm True Air Speed, fpm

52

54

64

76

86

59.8

64.1

74.3

86.2

96.7

98

144

184

230

274

T = 20 . 9°C

B = 758.4 nun Hg

107.8

157

199

249

298

‘

Table E4

Abbirko Flowmaster

S/N 6184

Low Range 1

Indicated Air Speed, fpm True Air Speed, fpm

48

50

60

74

84

54.9

60.0

72.1

82.8

94.4

98

142

184

228

272

T = 22. 2°C

B = 750.3 mm Hg

1 106.8

155

198

248

299

t
Table E5

Abbirko Flowmaster

S/N 6184

Low Range

Indicated Air Speed, fpm True Air Speed, fpm

50

52

60

76

84

56.6

60.7

72.1

84.2

95.3

98

142

182

228

272

T = 22. 3°C

B = 751. 1 mm Hg

Table E6

Abbirko Flowmaster

S/N 6184

Medium Range

106.4

155

199

249

298

Indicated Air Speed, fpm True Air Speed, fpm

30

55

75

170

265

63.4

86.1

108.1

190

299

370

475

585

685

402

507

611

716

T » 20. 8°C

B = 758.4 mm Hg
Table E7

Abbirko Flowmaster

S/N 6184

Medium Range

Indicated Air Speed, fpm True Air Speed, fpm

25 64.4

55 86.1

80 108.2

170 200

270 298

375 401

480 507

585 612

685 716

T = 20 . 9 °C

B = 758.4 mm Hg

Table E8

Abbirko Flowmaster

S/N 6184

Medium Range

Indicated Air Speed, fpm True Air Speed, fpm

25 59.9

50 82.8

75 106.2

165 199

265 298

370 402

475 506

580 611

685 714

T = 22 . 2°C

B = 750.0 mm Hg

ft
Table E9

Abbirko Flowmaster

S/N 6184

Medium Range

Indicated Air Speed, fpm

25

50

80

170

265

375

485

585

690

True Air Speed, fpm

61.1

83.6

107.5

199

299

402

506

611

716

T = 22 . 3°C

B = 750 . 8 mm Hg

Table E10

Abbirko Flowmaster

S/N 6184

Medium Range

Indicated Air Speed, fpm True Air Speed, fpm

25 61.2

50 83.0

75 106.8

170 199

265 299

375 402

480 506

585 611

685 717

T = 22 . 4°C

B = 751 . 2 mm Hg
Table Ell

Abb irk.o Fiovmascer

S/N 6184

High Range

Air Speed , fpm True Air Speed,

80 107.4

170 199

270 298

370 401

480 506

580 612

690 711

T = 20. 6°C

3 = 758.4 nm Hg

Table E12

Abbirko Flowraaster

S/N 6184

High Range

ndicared Air Speed, fpm True Air Speed, fpm

90 108.6

170 199

270 299

380 403

480 507

590 613

690 716

T = 20. 9°C

3 = 758.4 mm Hg
Table E13

Abbirko Flovmastar

S/N 6184

High Range

Indicated Air Speed, fpm True Air Speed, fpm

90 106.3

180 198

280 299

380 401

490 505

590 612

695 712

T = 22. 1°C

3 = 750.0 mm Hg

Table E14

Abbirko FlcTraaster

S/N 6184

High Range

Indicated Air Speed, fpm True Air Speed, fpm

90 106.7

180 199

280 299

380 403

490 507

590 611

695 715

T = 22 . 3°C

3 = 751.1 mm Hg
Table E15

Abbirko Flowmaster

S/N 6184

High Range

Indicated Air Speed, fpm True Air Speed, fpm

80 107.9

180 200

280 299

390 403

490 506

590 612

695 715

T = 22 . 4°C

B = 751.2 mm Hg
I

Table FI

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 F2

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
n

<A

- t

m

>

-(1

>ii

,|

ri

rl

ri

rn

in

>6

Table F3

Alnor Telcneter

Series 6000-?

Pitot probe-1250 Scale

True Air Speed

foa

100

HO

190

80

80

102

153

198

297

401

70

60

-98

605

706

21.3

• 10.1

AincT Vslosstfir

Series 5000-?

Pitot orobe—1250 Scale

Speed

True Air Speed

foa

00

10

53

35

~ 5

102

153

198

297

101

198

603

701

3 = 21.3 S C

'10.1 o= Ha
Table F5

Alnor Velometer

Series 6000-?

Pitot pro’oe-1250 Scale

Indicated Air Speed, True Air Si fpm tpa

100 102

140 153

192 198

285 291

378 402

470 497

560 602

648 709

car

T = 21.8 °C

B = 741.0 nm Hg

Table F5

Alnor Velatneter

Series 5000-P

Pitot probe-2500 Scale

Indicated Air Speed, True Air Soe

fpm fpm

75 103

125 U9

190 201

300 300

410 399

540 502

645 604

760 705

T = 21.1 °C

B = 749 .2 nun Hg
Table F7

Alnor Velometer

Series 6000-P

Pitot probe-2500 Scale

Indicated Air Speed,

f pm

True Air Speed,

fpm

75

130

190

295

420

103

149

200

299

399

540

655

755

503

604

707

T = 21.1 °C

B = 749.2 mm Hg

Table F8

Alnor Velometer

Series 6000-P

Pitot probe-2500 Scale

Indicated Air Speed,

fpm

True Air Speed,

fpm

80

130

195

300

435

103

149

200

300

399

540

650

755

503

606

706

T = 21.1 °C

3 = 749 . 3 mm Hg
Table F9

Alnor Velometer

Series 6000-P

Pitot probe-2500 Scale

Indicated Air Speed,

fpm

True Air Speed,

fpm

80

135

185

305

425

103

149

200

300

399

540

645

750

503

605

704

T = 21.1 °C

3 = 749 .3 mm Hg

Table F10

Alnor Velometer

Series 6000-?

Pitot probe-2500 Scale

Indicated Air Speed,

fpm

True Air Speed,

fpm

75

125

190

300

420

103

149

200

300

398

540

650

755

503

605

705

T = 21.1 °C

B = 749 . 3 mm Hg
Table Fll

Alnor Velometer

Series 6000-P

Diffuser probe-2500 Scale

Indicated Air Speed, True Air Speed

fpm fpm

75 101

145 148

230 201

395 301

540 401

675 501

820 602

940 701

T = 21.1 °C

3 = 747.8 mm Hg

Table F12

Alnor Velometer

Series 6000-?

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

= 21.1 °C

= 747 . 8 mm Hg

T

3
Table F13

Alnor Velometer

Series 6000-P

Diffuser probe-2500 Scale

Indicated Air Speed,

fpm

80

145

245

400

540

680

820

940

T =

3 «

True Air Speed,

fpm

101

149

200

301

401

499

601

699

21.1 °C

747 . 5 mm Hg

Table F14

Alnor Velometer

Series 6000-P

Diffuser probe-2500 Scale

Indicated Air Speed,

fpm

90

150

240

395

545

675

825

945

T =

B =

True Air Speed,

fpm

101

147

201

301

400

501

600

698

21.1 °C

747.5 mm Hg
Table F15

Alnor Velometer

Series 6000-P

Diffuser probe-2500 Scale

Indicated Air Speed,

fpm

True Air Speed,

fpm

90

150

245

395

540

101

148

200

301

400

680

815

940

500

599

698

T = 21.1 °C

3 = 747 . 3 mm Hg

Table F16

Alnor Velometer

Series 6000-P

Diffuser probe-1250 Scale

Indicated Air Speed,

fpm

True Air Speed,

fpm

135

195

280

395

510

101

149

199

300

401

620

735

840

498

601

698

= 21.1 °C

= 746.0 mm Hg

T

3
Table FI

7

Alnor Velometer

Series 6000-?

Diffuser probe-1250 Scale

Indicated Air Speed,

fpm

True Air Speed,

fpm

130

200

278

398

515

101

148

198

299

399

620

738

840

498

599

699

T = 21.1 °C

3 = 746.0 mm Hg

Table FIS

Alnor Velometer

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

500

602

697

T = 21.1 °C

B = 745.4 mm Hg
Table F19

Alnor Velometer

Series 6000-P

Diffuser probe-1250 Scale

Indicated Air Speed,

fpm

True Air Speed,

fpm

135

200

278

398

515

101

149

200

301

402

618

738

843

501

601

701

T = 21.1 °C

B = 745.4 mm Hg

Table F20

Alnor Velometer

Series 6000-P

Diffuser probe-1250 Scale

Indicated Air Speed,

fpm

True Air Speed,

fpm

138

200

275

395

518

101

148

199

301

401

620

738

840

499

603

696

T = 20.6 °C

B = 744.3 mm Hg
Table F21

Alnor Veloraeter

Series 6000-P

Low Velocity probe

Indicated Air Speed,

fptn

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 F22

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

T = 20.6 °C

B = 742.5 mm Hg
Table F23

Alncr Veloneter

Series 5000-?

Low Velocity probe

rdicated Air Speed, ron

True Air Speed,

fpm

32

46

67

92

42.6

56

77

101

149

29=> 199

270

T = 20.0 3 C

3 = 742.0 rm Hg

Table F24

Alncr Velcneter

Series 6000-P

Low Velocity probe

cated Air Speed, True Air Speed

fpn fpn

34 42.9

45 55 .

68 77.3

93 101

*7 /- / 149

208 198

295 271

T = 20.0 3 C

3 = 742.0 ran Hg

O'*

M
Table F25

Alnor Velometer

Series 6000-P

Low Velocity probe

Indicated Air Speed, True Air Speed

fpm fpm

33 42.3

13 56.9

53 77.6

94 102

144 149

207 199

296 272

T = 20.0 3 C

3 = 740.3 run Hg

Table G1

Alnor Velometer Jr.

Low Range

Indicated Air Speed, True Air Speed

fpm fpm

205 204.7

172 166.4

148 141.1

122 116.3

100 93.0

80 70.6

62 53.0

T = 26.9 °C

B = 747.5 mm Hg

Table G2

Alnor Velometer Jr.

Low Range

Indicated Air Speed, True Air Speed

fpm fpm

205 204.6

170 165.8

146 141.6

122 118.0

100 94.9

78 70.3

60 53.2

T = 26.9 °C

B = 747 . 5 mm Hg
Table 13

Alnor Velomecer Jr.

lew Range

True Air 5 oe

foui

200 204.2

170 166 .

143 242 i

120 117.0

100 92.7

80 70.7

52 53.3

3 = zo

Table G4

Alnor Telenerer Jr.

Low Range

. Air Speed, Tme Air Speed *“ fpn

:05 204.7

.70 166.3

.46 141.1

"70 1

- S\J 15.4

.00 92.9

30 59 .

62 53.4

3

26.9 °C

747.5 m

C
Alnor . glfiwoi-pr

-OV ?-ar.ae

Indicated Air speed.

red

205

170

102

80

52

^ J -

3

Table 2c

Alaor Telorerer Jr.

Indicated Air Speed,

fan

775

500

525

480

420

300

230

195

150

100

,r speed

,

fan

50 5 503

399

z «

93

in

T = 26.9 3 C

3 = 747.5 m rig
Table G7

Alnor Veiometer Jr.

High Range

ndicated Air Speed,

fpm

True Air Speed,

fpm

800

610

525

485

420

714 .

608.8

504.2

400.0

296.5

300

230

195

160

105

192.4

141.7

117.4

93.3

52.5

T = 26.9 °C

3 = 747.5 an Hg

Table G8

Alnor Veiometer Jr.

High Range

Indicated Air Speed, True Air Speed,

fpm fpm

800 714.2

610 609.7

530 504.9

480 399.3

420 296.9

300 191.8

210 140.3

180 117.4

150 93.0

100 53.3

T = 26.9 °C

3 = 747.5 mm Hg
Table G9

Alnor Velometer Jr.

High Range

Indicated Air Speed,

fpm

True Air Speed

,

f on

300

610

530

480

415

715.9

509.4

504.4

400.

296.

300

230

195

160

100

192.

141.

116.9

93.4

52.3

T = 26.9 °C

B = 747. 5 am Hg

Table G10

Alnor Velometer Jr.

High Range

Indicated Air Speed, True Air Speed

fpm fpm

800 715 .

7

625 610 .

6

530 504.6

480 399.0

420 296.3

300 191.5

225 141.0

195 115.4

160 92.3

100 54.4

T = 27.0 °C

B = 747.5 mm Hg

Ul

Ul

>.o

CO
I

!

i

i

i

i
Table HI

J-Tec Type VA-216

S/N 49

Instrument Output Frequency Instrument Output Voltage True Air Speed

Hz volts fpm

8.68 .132 60.3

10.9 .160 72.2

12.6 .182 81.0

14.6 ' .208 91.4

16 .

5

.233 100.6

22.7 .312 128

32.5 .44 170

46.9 .62 219

65.4 .88 284

83.2 1.12 374

110 1.48 492

147 1.95 649

187 2.45 835

242 3.20 1103

278 3.70 1290

318 4.20 1495

T = 21.3 to 21.6 °C

B = 752.4 mm Hg

i
Table H2

J-Tec Type VA-216

S/N 49

Instrument Output Frequency

Hz

Instrument Output Voltage

volts

True Air Speed

fpm

8.63

10.5

12.3

15.0

16.6

.126 60.8

.154 72.5

.175 81.6

.209 92.9

.229 100.8

22.9

32.6

46.9

66.2

84.0

.308 130

.44 172

.62 220

.86 284

1.13 375

112

148

186

245

276

1.49 492

1.95 647

2.50 833

3.20 1109

3.65 1293

320 4.15 1502

T = 22.5 °C

B = 752.7
Table H3

J-Tec Type VA-216

S/N 49

Instrument Output Frequency

Hz

Instrument Output Voltage

volts

True Air Speed

f pm

8.70

10.8

12.7

14.9

16.3

.130 61.6

.154 72.5

.180 81.6

.210 92.5

.226 100.2

23.0

32.6

47.4

65 .

4

84.0

.311 131

.43 171

.60 219

.86 285

1.13 375

112

147

186

245

282

1.48 492

1.96 648

2.47 834

3.21 1110

3.68 1298

318 4.16 1497

T = 22.5 to 22.8 °C

B = 752.8 mm Hg
Table H4

J-Tec Type VA-216

S/N 49

Instrument Output Frequency

Hz

Instrument Output Voltage

volts

True Air Speed

fpm

8.59

10.6

12.6

14.8

16.3

.126 59.8

.154 71.1

.175 80.5

.209 91.9

.227 100.4

22.7

32.7

46.7

64.9

82.6

.308 131

.43 171

.60 219

.86 286

1.12 374

110

148

189

243

279

1.48 493

1.97 648

2.46 835

3.20 1106

3.65 1286

4.19

T = 22.8 to 23.0 °C

B = 752.8 mm Hg

316 1505
Table H5

J-Tec Type VA-216

S/N 49

Instrument Output Frequency

Hz

Instrument Output Voltage

volts

True Air Speed

fpm

8.50

10.8

12.6

14.9

16.4

.126 59.5

.152 71.5

.177 80.9

.207 92.1

.226 100.2

23.3

32.8

46.5

65.4

83.3

.313 130

.43 172

.61 220

.84 284

1.12 375

110 1.48 490

147 1.96 648

188 2.47 836

244 3.20 1111

279 - 3.65 1292

320 4.12 1502

T = 23.2 to 23.4 °C

B = 751 . 3 mm Hg
.
Table II

J-Tec Type VA-216

S/N 48

Instrument Output Frequency,

Hz

Instrument Output Voltage, True Air Speed,

volts fpm

8.61

10.8

12.6

14.7

16.3

.118 59.6

.146 71.0

.168 80.4

.195 92.0

.216 100.5

22.2

30.8

46.3

59.5

82.6

.29 130

.40 172

.60 220

.78 286

1.09 375

106.8 1.43 494

145.6 1.91 650

185.2 2.44 832

T = 23 . 1°C

B = 751.0 mm Hg
Table 12

J-Tec Type VA-216

S/N 48

Instrument Output Frequency,

Hz

Instrument Output Voltage,

volts

True Air Speed,

fpra

8.48

10.7

12.5

15.0

16.2

.116 58.1

.144 70.3

.166 80.2

.199 93.0

.215 99.5

22.2

29.7

46.1

57.5

82.0

.295 130

.39 170

.60 219

.76 285

1.09 375

105.7

144.5

186.2

1.42 494

1.92 649

2.45 835

T = 23. 4°C

B = 751.2 mm Hg
Table 13

J-Tec Type VA-216

S/N 48

Instrument Output Frequency,

Hz

Instrument Output Voltage,

volts

True Air Speed,

fpm

8.65

10.9

12.7

15.0

16.4

.117 59.6

.147 71.9

.169 81.0

.198 92.9

.218 100.9

23.0

29.2

45.7

57.8

80.0

. 29 130

.38 171

.60 220

. 77 285

1.07 375

106.4 1.49 492

143.7 1.91 650

184.8 2.45 836

T = 23. 7°C

B = 750.8 mm Hg
Table 14

J-Tec Type VA-216

S/N 48

Instrument Output Frequency,

Hz

Instrument Output Voltage,

volts

True Air Soeed,

fpm

8.50

10.6

12.5

14.7

16.3

119 63.5

142 71.2

166 80.1

196 91.8

217 100.2

21.5

28.8

45.2

59.9

78.1

.28 130

.38 170

.59 220

. 78 284

1.04 375

107.0

143.5

186.2

1.40 492

1.90 647

2 . 44 834

T = 23. 9°C

3 = 750. 2 mm Hg
Table 15

J-Tec Type VA-216

S/N 48

Instrument Output Frequency,

Hz’ Instrument Output Voltage, True Air Speed,

volts fpm

8.40

10.6

12.4

14.6

16.2

.06 63.6

.142 70.4

.165 80.0

.195 91.1

.215 99.4

22.7

27.9

44.8

60.2

78.1

.30 130

.37 170

.59 219

.77 283

1.04 375

103.7

142.9

184.8

1.58 489

1.88 642

2.43 834

T = 24 . 2°C

B = 750. 2 mm Hg

Table J1

Thermogage Air Velocity Meter

Instrument Output,

ua

99

89

80

70

58

44

27

16

9

8

True Air Sneed,

f pm

138 .

7

119.2

101.8

85.4

70.0

54.8

39.2

27.9

22.1

17.7

T = 22.2 °C

3 = 752.8 mm Hg

Table J2

Thermogage Air Velocity Meter

Instrument Output, True Air Sneed.

ua f pm

100 138.7

91 119.1

81 102.7

70 86.4

58 69.8

45 54.7

26 37.5

18 30.4

11 23.4

7 15.8

T . = 22.2 °C

3 = 752.8 mm Hg
Table J3

Thermogage Air Velocity Meter

Instrument Output, True Air Speed

ua rpm

99 137.9

90 119.1

81 102.7

70 86.3

58 70.0

44 54.3

26 38.2

18 29.8

11 23.0

9 20.1

3 = 752.8 mm Hg

Table J4

Thermogage Air Velocity Meter

Instrument Output, True Air Soeed

ua fpm

100 138.6

90 118.9

81 101.8

71 86.5

58 69.5

43 53.6

24 35.6

17 28.7

12 23.6

8 19.4

= 22.2 °C

= 752.8 mm Hg

T

3
Table J5

Thermogaae Air Velocity Meter

Instrument Output, True Air See ua f nm

99 140.0

91 119.1

82 102 .

2

69 85.0

57 68.4

43 52.9

27 35.7

13 29.9

11 21.7

9 18.6

T = 22.0 °C

B = 752.8 tun Hg

Table K

INSTRUMENT

A, vane

B , vane

C, vane

D , vane

E , vane

F, * impact-def lection,

low and high ranges

F, * impact-deflection,

low velocity probe

G, * impact-deflection,

low range

G, * impact-deflection,

high range

H, vortex-shedding

I, vortex-shedding

J, * heated-foil

Minimum Operating Speeds

STOPPING SPEED (fpm)

54

18.2

60.6

31.7

39.5

100

40

53.0

50.8

54.1

58.8

16

STARTING SPEED (fpm)

63.3

23.3

66 .

6

47.8

59.6

*Determined by resolution

Top

View

FIGURE

1.

SCHEMATIC

OF

FLOW

FACILITY.
FIGURE 2. INSTRUMENT A MOUNTED IN THE TUNNEL, SHOWING METHOD OF SUPPORT
FIGURE 3 INSTRUMENT B MOUNTED IN THE TUNNEL, SHOWING METHOD OF SUPPORT.
FIGURE 4. INSTRUMENT C MOUNTED IN THE TUNNEL, SHOWING METHOD OF SUPPORT.
FIGURE 5. INSTRUMENT D MOUNTED IN THE TUNNEI, SHOWING METHOD OF SUPPORT

.
FIGURE 6. INSTRUMENT E MOUNTED IN THE TUNNEL, SHOWING METHOD OF SUPPORT
FIGURE 7. INSTRUMENT F WITH PITOT PROBE MOUNTED IN TUNNEL

SHOWING METHOD OF SUPPORT.
FIGURE 8. INSTRUMENT F WITH DIFFUSER "PROBE MOUNTED IN TUNNEL

SHOWING METHOD OF SUPPORT.
FIGURE 9. INSTRUMENT F WITH LOW-VELOCITY PROBE MOUNTED IN TUNNEL

SHOWING METHOD OF SUPPORT.
FIGURE 10. INSTRUMENT G MOUNTED IN THE TUNNEL, SHOWING

METHOD OF SUPPORT (VIEWED LOOKING DOWNSTREAM)

.
FIGURE 11. INSTRUMENTS H AND I MOUNTED IN TUNNEL, SHOWING

METHOD OF SUPPORT (VIEWED LOOKING DOWNSTREAM)

.
FIGURE 12 INSTRUMENT J MOUNTED IN TUNNEL, SHOWING METHOD OF SUPPORT.
b*

C£<

>

CiJ 3OHI

tu

DISTANCE

UPSTREAM

FROM

ANEMOMETER

(cm)
o o

in

eM

>

3 =5

DISTANCE

UPSTREAM

FROM

ANEMOMETER

(cm)

E

I

CURE

14.

VARIATION

IN

VELOCITY

WITH

DISTANCE

UPSTREAM

OF

INSTRUMENT

PKOIJE.

U

tu

=

7()

fpifc

.
FIGURE 15. DEFINITION OF TERMS FOR CALCULATION OF a..
U (fpm)

FIGURE 16. INDICATED VERSUS TRUE VELOCITY WITH ± 2 a CURVES. INSTRUMENT A.

800

700

600

500

400

300

200

100 '

0

-4 iFIGURE 18. INDICATED VERSUS TRUE VELOCITY WITH ± CURVES. INSTRUMENT C.
FIGURE 19. INDICATED VERSUS TRUE VELOCITY WITH ± 2 a CURVES.

INSTRUMENT D.
4-

U (fpm)

FIGURE 20. INDICATED VERSUS TRUE VELOCITY WITH ± 2 a CURVES,

LOW RANGE. INSTRUMENT E.
4 4 4 4

700

600

500

(fpm)

400

300

200

100

0 4 * —

o 100 200 300 400 500 600 700

U (fpm)

FIGURE 21. INDICATED VERSUS TRUE VELOCITY WITH ± 2a CURVES,

MEDIUM RANGE. INSTRUMENT E.
FIGURE 22. INDICATED VERSUS TRUE VELOCITY WITH ± 2 a CURVES,

HIGH RANGE. INSTRUMENT E.
u.

1

(f pm)

U (fpm)

FIGURE 23. INDICATED VERSUS TRUE VELOCITY FOR PITOT PROBE

INSTRUMENT F

.

LOW RANGE-
800

U (fpm)

FIGURE 24. INDICATED VERSUS TRUE VELOCITY FOR PITOT PROBE, HIGH

RANGE . INSTRUMENT F

.
900

0 100 200 300 400 500 600 700 800 900

U (fptn)

FIGURE 25. INDICATED VERSUS TRUE VELOCITY FOR DIFFUSER PROBE, LOW

RANGE. INSTRUMENT F.
u.

1

(fpm)

U (fpm)

FIGURE 26. INDICATED VERSUS TRUE VELOCITY FOR DIFFUSER PROBE

HIGH RANGE. INSTRUMENT F.

1
“

I

I

Itu.1

fpm)

3 100 200 300 400 500

U (fpm)

FIGURE 29. INDICATED VERSUS

INSTRUMENT G. TRUE VELOCITY WITH

600 700 800

2 ct CURVES, HIGH RANGE.

i
FIGURE 30. PULSE FREQUENCY VERSUS TRUE VELOCITY WITH ± 2 a CURVES,

INSTRUMENT H. 1
U (fpm)

FIGURE 31. PULSE FREQUENCY VERSUS TRUE VELOCITY WITH ± 2ff- CURVES.

INSTRUMENT I.
U (fpm)

FIGURE 32. OUTPUT OF INSTRUMENT J AGAINST VELOCITY

.
3

FIGURE

13.

DEVIATION

OF

INDICATED

FROM

TRUE

VELOCITY.

INSTRUMENT
U

(

i

pm

)

FIGURE

34.

PERCENT

DEVIATION

OF

INDICATED

FROM

TRUE

VELOCITY.

INSTRUMENT
ft r |

3

i 3

FIGURE

35.

DEVIATION

OF

INDICATED

VELOCITY

FROM

TRUE

VELOCITY.

INSTRUMENT
80 + + o

Q

I 70 _ G

O

-10 1 j 1 1 1 ! 1 0 100 200 300 400 500 600 700

U Ofpm)

FIGURE 36. PERCENT DEVIATION OF INDICATED VELOCITY FROM TRUE VELOCITY.

INSTRUMENT 3.
111

(fpm)

KTG,,KK

V/

•

DEVIATION

OF

INDICATED

VELOCITY

FROM

TRUE

VELOCITY.

INSTRUMENT
100

U

(fpm)

FIGURE

38.

PERCENT

DEVIATION

OF

INDICATED

VELOCITY

FROM

TRUE

VELOCITY.

INSTRUMENT'
FIGURE

39.

DEVIATION

OF

INDICATED

VELOCITY

FROM

TRUE

VELOCITY.

INSTRUMENT

I)
IJ

(fpm)

FIGURE

40.

PERCENT

DEVIATION

OF

INDICATED

VELOCITY

FROM

TRUE

VELOCITY.

INSTRUMENT

D.
4 ^ + 4 + 1 1 1 I I

1- 4 4 4

4 4

—

—

ocn o

CM O

s

Q.

u-j 3

I 3
+ +
I

0

100

200

100

/,()()

500

000

700

0,

(f|>m)

I'lOOUli

VI

DEVIATION

OF

INDICATED

VELOCITY

FROM

TRUE

VELOCITY,

MEDIUM

KANCK.

INSTRUMENT
li (

f

pin)

FIGURE

44.

PERCENT

DEVIATION

OF

INDICATED

FROM

TRUE

VELOCITY,

MEDIUM

RANGE.

INSTRUMENT



3I 3

5^ 3r*Z<3J

Id3

a;c i c;3>

Cd

Cd

S-<aC i

Cd "V* 3 i, — in. X3 z

ooa3
•H

!=>

I

!=>

6

ex

»4-l

FIGURE

49.

DEVIATION

OF

INDICATED

VELOCITY

FROM

TRUE

VELOCITY

FOR

PITOT

PROBE,

HIGH

RANGE.

INSTRUMENT

F.
U

(I

pui)

FIGURE

50.

PERCENT

DEVIATION

OF

INDICATED

FROM

TRUE

VELOCITY

FOR

PITOT

PROBE,

HIGH

RANGE

.

INSTRUMENT

F.
(fplll)

DEVIATION

OF

INDICATED

VELOCITY

FROM

TRUE

VELOCITY

FOR

DIFFUSER

PROBE 1

01!

RANGE

INSTRUMENT

F.
(mdj)

PERCENT

DEVIATION

OE

INDICATED

FROM

TRUE

VELOCITY

FOR

DIFFUSER

PROBE

LOW

RANCE

INSTRUMENT

F.
•H p ^

e

i a.

U-4 3 w

FIGURE

53.

DEVIATION

OF

INDICATED

VELOCITY

FROM

TRUE

VELOCITY

FOR

DIFFUSER

PROBE,

HIGH

RANGE

.

INSTRUMENT

F.
U

(fpm)

FIGURE

r

>4.

PERCENT

DEVIATION

OF

INDICATED

FROM

TRUE

VELOCITY

FOR

DIFFUSER

PROBE,

HIGH

RANGE

.

INSTRUMENT

F.
o c

pH

I 0

CN

1 Om

I

3

I 3

Ea

'-H

FIGURE

55.

DEVIATION

OF

INDICATED

VELOCITY

FROM

TRUE

VELOCITY

FOR

LOW

VELOCITY

PROBE.

INSTRUMENT

F.
I

II(

f

pm)

FIOURE

5(>.

PERCENT

DEVIATION

OK

INDICATED

FROM

TRUE

VELOCITY

FOR

LOW

VELOCITY

PROBE

INSTRUMENT

F.
>-><> I
INSTRUMENT
J-

: i 5 i

{ J r o

CM O o o

<T 0

VC

1 0

00

1

o

o

0

CM

1

<

as

CJ

>

o

o

<

>

U~1 a

5

o

I

3

I C.

U-l 3

INSTRUMENT
INSTRUMENT
II f(

pill

)

I'lUIKK

61.

STANDARD

DRV I

ATI

ON

AND

COKKRCTRI)

STANDARD

DRV I

AT

ION

IN

TRIMS

DR

TRUE

VELOCITY.

I

NSTRUMENT

A.
-

U

(I

pm)

FICIJRf

62.

o

AND

o

AS

PERCENT

OF

CROUP

MHAN

TRUE

VELOCITY.

INSTRUMENT
KlttllKIS

6'J.

STANDARD

DEVIATION,

o

,

AND

CORRECTED

STANDARD

DEVIATION

o

IN

TJiKMS

OK

TRUE

Vlil.OO

ITY

.

INSTRUMENT

li

.

o 3 c:

"3" ft CM

U(f

pm)

STANDARD

DEVIATION,

o,

AND

CORRECTED

STANDARD

DEVIATION,

o.-

INSTRUMENT


n
2.01

es CN

o

o

o

Q.

M—

(

FIGURE

69.

a

AND

a

IN

TERMS

OF

TRUE

VELOCITY,

LOW

RANGE

.

R/2

NOTED.

INSTRUMENT
0

! is
u D

O

K/2

NOTKI).

I

NSTKUMKNT

men

RANCH.

R/2

NO'I'KI).

I

NSTKIIMKNT
o
U

(fpm)

IN

TERMS

OK

TRUK

VELOCITY

FOR

NTOT

I’ROISE,

LOW

RANCH

.

R/2

NOTED

.

INSTRUMENT
R/21J

FIGURE

76.o

ANDoc

AS

PERCENT

OK

CROUP

MEAN

VELOCITY

FOR

PITOT

PROBE

NOTED.

INSTRUMENT

K.
2: o w
-I

K/2U

fcj 2<

csOC>2 H >

u-i Z<

Cd 1= 22o

as • u aCs« Li O 2 2 ~ a CS 2 =- — V} a 2

a.

—

c/3 • < 2

£d

tfcC“ O2

5(2 < CM o si o , O 1 2

CM l=T ~T D

5^

FIGURE

78.
*

o
R/21J
aoo 0

100

200

300

400

500

600

700

U

(f

pm)

FIGURE

81.o

ANDa

IN

TERMS

OF

TRUE

VELOCITY

FOR

DIFFUSER

PROBE,

HIGH

RANGE.

R/2

NOTED.

INSTRUMENT

F.
K/

211

U/2U
o
2

.0"f

yo 1 = Oil 13

Csl S'® o I |3


STANDARD

DKVIATION

OR

I'Ul.Sli

RKKQUKNOY

.

INSTRUMENT

II.
INSTRUMENT

II.
v:
FIGURE

92.

o

AND

o

AS

PERCENT

OF

GROUP

MEAN

VELOCITY.

INSTRUMENT

II.
+ + f - ¥ * i ,* 4

-, * _

II(

I

pill)

TANDAIU)

l)l'!V I

AT

ION

OK

I'lH.SK

KKI5QIIKNCV

.

I

NSTKIIMKN'I

I'laiKK

r>

.

STANDAKI)

DI5V I

AT

ION

,o

,

AND

COKKKCTHI)

STANDARD

DEVIATION,

o

.

KXI'KKSSISO

EQUIVALENT

THIII2

VELOCITY.

I

NSTKIIMISNT

I.

C
?% 9 ?

U

(fpm)

FIGURE

96.

a

AND

a

AS

PERCENT

OF

CROUP

MEAN

VELOCITY.

INSTRUMENT
.V A + + JL «*.

1.4

1.2

1.0

I

a)

0.8

0.6

0.4

0 . 2

20 40 60 80 100 120 140

U (fpm)

FIGURE 97. STANDARD DEVIATION OF INSTRUMENT OUTPUT AGAINST GROUP MEAN

VELOCITY. INSTRUMENT J.
10

9

8

7

6

5

4

3

2

1

0
1.6 A_ JL +

1.4

1.2

1.0

0.8

',a ,R/2

c

( f pm)

0.6

0.4

0.2

0

* 4

0 20 40 60 80 100 120 140

U (fpm)

FIGURE 99. STANDARD DEVIATION AND CORRECTED STANDARD DEVIATION IN

TERMS OF VELOCITY. R/2 NOTED. INSTRUMENT J.
|

|Q

-i ! 1 < I ! »

f—... 4, . - 1 1.

0 4 1 1——I 1 1 I 1 I 1 1 1 I (—

0 20 40 60 80 100 120 140

U (fpm)

FIGURE 100. STANDARD DEVIATION IN .TERMS OF VELOCITY AS PERCENT

OF GROUP MEAN VELOCITY. R/2U NOTED. INSTRUMENT J.