BRUEL & KJAER 2211 User guide

Noise Limit Indicator
Type 2211
Type 2211 Noise limit Indicator is a noise and
vibration analyzer designed to keep control on
the noise or vibration produced by units leaving
a production line.
BHUEL&KJJEH
NaHum, Denmark . eyf;' 80 05 00 . ~ BRUKJA, Copenhagen . Telex: 5316
BB 2211

Noise Limit Indicator
Type 2211
Reprint April 1963

Contents
Introduction to the Instrument . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Introduction to Noise and Vibration Measurements on products . . . . . . . . 4
'Vid eband Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Weighted Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Frequency Analysis of Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Measurements in Selected Frequency Bands . . . . . . . . . . . . . . . . . . . . . . . . 7
Capabilities of the Noise Limit Indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Which data must be known be · fore the Instrument is used .............. 10
Wb.at should be measured, Noise or Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Practical arrangements when "setting up" the Instrument .............. 14
· vibration testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Noise testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Use of the Noise Limit lndicatol' ...................................... 19
Pre-adjustments . ..... ................................ .... ..... .. 19
Adjustment for use with Microphone Type 4131 -32 . . . . . . . . . . . . . . . 19
Adjustment with
1
h" Microphone ................................ 25
Vibration Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Adjustment of the "Sensitivity Increase" .......................... 28
Operators Instruction ............................................ 31
Use of both Inputs sim ult aneous ly ... .. ....... .... ....... ....... .. 32
Remote Control .................................................. 34
Technical Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Input Amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Filters and Output Amplifiers ........ ... .............. .. ...... ... 37
Rectifier and Relay Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Contro l Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
l\feter Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Power Supply .......... .... .... .. .... ... ............ .... . ...... . 41
Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Introduction
The Noise Limit Indicator is an instrument designed to provide a rapid
and accurate evaluation of the quality of products on a production line with
respect to noise and vibration. This is achieved by measuring the noise
and vibration of every unit leaving the production line and comparing the
result with the noise and vibration level obtained from the "standard"
unit.
The instrument has been designed to offer the utmost simplicity in operation.
After setting-up, an unskilled worker can easily interpret the indicating
panel and thereby the acceptance or rejection of the unit manufactured.
Rejections are indicated by red indicating lamps. In this way the possibility
of confusion or errors from meter readings is completely eliminated.
The instrument measures noise and vibration in several frequency bands (up
to 12 bands ) simultaneously. The operator 's job is simplified to such a
degree that he only presses a button and notes if any lamp lights up. If
These units ore bought seperotely
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Control Panel
Fig. 1. The Noise Limit Indicator shown with the necessary extra items for
the measurement of noise and vibration. Two input channels and twelve
output channels with filters can be plugged in.

a lamp lights, the operator labels the unit just tested with a number
corresponding to that of the lamp, and directs the rejected unit to the
repair shop. The number of the indicating lamp informs the repair shop
of the frequency at which the presset limit has been exceeded, thereby often
giving the shop a hint as to which problem has to be corrected.
The total operation time for the assessment by the apparatus is extremely
short. When set-up practically, the testing for noise and vibration can
normally be carried out in less than ten seconds for each unit.
The apparatus is devided into units so that only the transducing elements ,
i.e.
the microphone or vibration pick-up, need fo be near the production
line. The main unit containing the amplifiers and filters can be placed some
distance from the production line and the control panel with indicating
lamps may be placed wherever it is found most convenient for the operator.
As shown in Fig. 1 the main assembly containing power supply, meter
circuit, input amplifiers and output amplifiers is, to ' gether with the control
· panel, supplied as the basic assembly to which can be added a condenser
microphone, a vibration pick-up, and as many filters as are found necessary
for the measurements in question. Microphone and vibration pick-ups arc
readily connected by plugs on the rear of the instrument , and output am
plifiers and filters are made as plug-in units which are easily interchange-
able. The electrical and acoustic specification of the instrum e nt is fully
described on page 43-44.
INTRODUCTION TO NOISE AND VIBRATION MEASUREMENTS
ON PRODUCTS
The measurement of noise and vibration may be carried out in several ways.
depending upon the purpose of the measurement. Some of the most
commonly used methods are discussed below in order to give a summary
of the reasons for measuring noise from production line uni Is in frequency
bands. Noise and vibration in most respects act in a similar manner , thu,;;
the term "noise" will be used, and vibration will only be mentioned where
noise and vibration act in a different way.
Some of the most common methods of measuring noise levels are:
a) wideband measurements, i.e. by means of instruments with a uniform
response to all audible frequencies.
b) noise measurement with instruments that have "weighted" characteristics .
c) frequency analysis of noise.
d) measurement in selected frequency bands, i.e. with instruments thai
measure noise in certain pre-selected frequency bands only.

a) \Videband Measurements·
Wh en making wid eba nd nwasurements of noise levels, an in s trum e nt is used
that res ponds e qually to noi 'Se of all fr e qu e ncies within the audible rang e,
which is from 20 c/s to 20ooo c/s approximately. This m ea ns that the
measuring instrum e nt gives the same indication for all sounds of e qual
physical "strength", whether the sound is of low , me dium or high pitch .
vVh en m eas uring noi se co ntaining several fr e qu e nci es, the wid e band measurin~
instrument will defl ect to a value which is proportional to th e sum of energy
co ntents in all th e diff ere nt noise frequencies represented. See Fig. 2. Thi s
typ e of m eas urem e nt is used wher e it is des ired to measur e th e overall
sound pressur e level at a certain place. (S .P.L. in db is usually with ref ere ncP.
to the accepted hearing threshold: o.0002 t-tbar).
ir·r:::;.
Frequency
Microphone \
Fig. 2. Wideband measurement of nois e. The meter will give an indication
which is slightly above the top of the highest peak noted in the frequency
spectrum. Noise of all frequencies passes unattenuated to the meter.
b) "\Veigh ted" Measurements.
\Veighted m eas ur eme nt s are measur eme nts taken with instrum e nts which
hav e respons e c urv es that , to a certain degree, follow thos e of th e human
ea r. The human ea r appears to be most sensitive to medium frequencies and
is th er efo re not so irritat ed by low or high pitched nois e. The frequency
r espo nse of "weig ht ed" measuring in s trum e nts is then shaped in such a way
as to approximate th e se nsitivity curves of th e human ea r. This is normally
done by ins e rtion of one or more filt e rs in a wideband amplifier. Thr ee
different filter chara ~ t e ristics have been int e rnationally standardized for thi s
purpose.
•) An instrument with a wideband response may also be referred to as one with a
response which is linear, overall, or flat.
5

In the measurement of noise containing several frequencies, the instrument
measures the nois e as th e sum of the energy contents after the frequency
weighting has taken place , see Fig. 3. Weighted measurements are mainly
used in cases where it is desired to investigate noise interference of working
conditions etc. The result read off an instrument with weighted characteristics
is the sound level (different from sound pressure lev e l) and is stated in db
SL (= db de . 2 X lo -4 .ubar), curve A, B or C.
Frequency
Microphone
Frequency Weighted
Level
- -0
Frequency
162207
Fig. 3. Weighted measurements. As . ~hown the noise spectrum is shaped by
means of a filter so that parts of the noise is depressed and only the medium
frequencies are allowed to pa.ss unattenuated. That means that the medium
frequencies have a predominant influence on the meter indication.
c) Frequency Analysis of Noise.
Frequ e ncy analysis is carried out by instruments that are capable of selecting
and measuring specific noise frequency bands only, although several other
noise frequencies may be present. The frequencies can be selected by means
of a series of filters which are successively inserted in a wideband measuring
instrument, and which make the instrument sensitive to only a certain
frequency band at a time, see Fig. 4. Usually in noise measurement the
audible frequency range is divided into a number of bands of equal relative
bandwidth. Thus, an octave band analyzer divides the audible range into Hl
bands, eac h with the width of one octave; a 1 h octave band analyzer divides
6

~r·es.
l, Microphone
Frequency
Frequency
Noise band Level
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c
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L.E
Frequency
1622.05
Fig. 4. Analysing noise by means of a series of narrow band filters that
can be inserted successively in the amplifier. Only the noise having a
frequency that falls within the range of the inserted filter is passed to the
meter. The meter indication in this way becomes frequency depei..dant.
the range into 30 bands, each
1
h octave wide. An example of such an
analyzer is the B & K Type 2112 mentioned on page 11. With an analyzer
of this type the noise band lev el can be measured at any arbitrary frequency
without any disturbing influence from other (and perhaps "s tronger ") sounds
arriving at the microphone simultaneously. In this way it is possible to
investigate which frequencies are predominant, measure their "strength" and
character and thereby arrive at a method for treatment of the noise problem.
Bands narrower than
1
h octave are not normally used in noise measurements;
however , in the investigation of vibration, an ana lyz er with filters having
a width of less than
1
h octave would often be employed. The B & K Type
2107 is an examp le of such an analyzer.
d) Measurements in Selected Frequency Bands.
Once laboratory investigations have been carried out upon objects from a
production lin e (or on the prototypes) and the noise and vibration generated
by the objects is analysed e.g. by means of an ana lyz er as mentioned above ,
it
can be calculated which of the noise frequencies must be checked in
production. Often, attention may be confined to certain important frequencies
ortly, and other bands ignored. A special instrument which measures these
particular noise frequencies ( see Fig. 5) can then be used to cheek the units
7

from the production lin e. Such an instrument is the Noise Limit Indicator
Type 2211. It measures noise or vibration in a number of pre-selected
frequency bands simultaneous ly. The bandwidth can be chosen to be 1 octave
or
1
h octave, depending on the cond itions.
lr
5
ES.
Microphone Frequency
Filter characteristics
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Filters /
Frequency c
0
rfiDI1 11r: =I
Frequency
16 220 6
Fig. 5. This figure shows the measuring principle of the Noise Limit
Indicator. Several filters are ins erted. The meter is substituted by reel lamps,
so that tl1ere is an indicator for each filter. Thereby the excess of the
noise band limits of several filters can be indicated simultaneously. The
filter attenuation can be adjusted for each filter incliviclually.
The noise frequency bands and the levels set as the maximum limit for each
of the bands sel ected should be chosen as a result of careful · laboratory
investigation of the object to be examined. It may also be desirable to keep
a check on the overall noise level of the object by means of wideband and
weighted measurements. The Noise Limit Indicator is capable of checking a
number of pre-selected frequency band levels as well as the overall noise
level , both wideband and weighted , simultaneously.
CAP ABIT .. ITIES OF THE NOISE LIMIT INDICATOR
The equipment can be used for a wide range of tests, since a number of
measurements can be carried out simultaneously with the Noise Level
Indicator. Some af the most commonly used measurements that can be made
with the instrument are: -
R
1) Simple "go-no go" testing for noise or vihration or both simultaneously
( see Fig. 6a).