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.
BRUEL&KJ~R
N..Hum, D enmark . fE 800500 • ;;> BRUKJA, Copenhagen . Telex: 5316
BB 2211

Noise Limit Indicator
Type 2211
Reprint february 1966

Contents
Introduction to the Instrument ........... . .. .. ................. .. ... 3
Introduction to Noise and Vibl'ation Measurements on products ..... . .. 4
'Videband Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . f)
Weighted Measurements ..................... ..... ................ 5
Frequency Analysis of Noise. . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. 6
Measurements in Sel ected Freq u ency Bands ........................ 7
Capabilities of the Noise Limit Indicator .............. ....... .. . .. .... 8
Which data must be known before the Instrument is used ... . ...... ... . 10
What s hould be measured, Noise or Vibration . . . . ........ ..... . . . . . . . .. 13
Practical arrangements when "selling up" the Instrument . ............. 14
Vibration testing . .. . ............... . ...... .. ........ . .... ....... 15
Noise testing ................... . ...... . . . ........ .. ... .. .... . ... 16
Use of the Noise Limit IndicatOl' .... .... ....... ..... ..... . .......... .. 19
Pre-adjustments ..... . ......... .. .................. . . .. .......... 19
Adjustment for u se with Microphone Type 4 131-32 ....... . ...... 19
Adjus tm e nt with lh" Mic rophone .............................. . . 25
Vibration Measurement .................. . .... . ................ . . 25
Adjustment of the "Sens itivit y Increase" .... .. . ... .. . ............. 28
Operators Instructi on . ... . ... ........... ....... . ......... .. ...... 31
Use of both Input s sim ult aneous ly .. .. . . ...... . . . .. ... ............ 32
Remote Control ... ................ .. ....... ... ........ .. ......... 34
Technical Description .. . .............. . ..... .. . .... ... ...... ........ 36
Input Amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 36
Filters and Output Amplifiers ............. .. . . .... . ............ . . 37
Rectifier and Relay Circuit ................ . ....... .. ... . . . ...... 39
Control Panel ................... . . . ................... . ..... .. .. . 40
Meter Circuit .... ..... ... .. ....... ... ............. .... . . .... . .... 41
Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Specification ..................... . ................... .. .... . .. . . . ... 43

Introduction
The Noise Limit Indicator is an instrument designed to provide a rapid
a nd accurate evalulltion of the quality of products on a production line with
respect to noise and vibration. This is achieved by measuring the nois e
and vibration of every unit leaving the production line and c omparing the
result with the noise and vibration level obtained from the "standard"
unit.
The instrument has be en designed to offer the utmost simplicity in operation.
After setting- up, an unskilled worker ca n easily interpr et the indi ca ting
panel and thenby the acce ptance or rejection of the unit manufactur ed.
Rejections are indicated by red indicati,ng lamps. In this way the possibility
')f confusion or errors from meter readings is completely eliminated .
fhe instrument measur es noise and vibration in several frequency bands (up
to 12
bands ) simultaneously. The operator's job is simplified to sH ch a
de
gree that he only presses a button and notes if any lamp lights up . If
These units ore bought seperat e ty
~rurL ng ..tbf. Jlgig llmjt lrlIIiootor
I .--Cathode FoUoWlr
2613
1
I I
1 Microphone 4131 I
1 I
I I
I I
1
1
1
1 ..-- --- --,
ISet of 33 'Il octave filters
I l~i ~ 5 ~~ C~.5 ~~ C~,5
I 50" 63 .. 80 ..
I 100" 125 ·· 160"
I 200 - ~: :: ~;~: :
I ~~~ : : 1000" 1200··
I 1600 -2000 ·· 2500··
1 3150
.• 400!}· 500!)' I
I 6300 ·· 8000 ·· 10000·· I
IJ: __ .:....._~. __ _ .. ='J
162202
QQQQQQ
QQQQQQ
00 ... "::...,,.,.
• ••••
~ .. ~ ... ::::"'!.. .. - ......
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.
3

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,
Le. the microphone or vibratioll pick-up, need to be near the production
line. The main unit containing thl' 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, together 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 instrument 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 units in frequency
bands . Noise and vibration in most respects act in a sim · ilar manner, thus
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:
1.
a) wideband measurements, Le. 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, Le . with instruments thai
measure noise in certain pre-selected frequency bands only.

a) 'Videband Measurements·
When making wideband measurements of noise levels, an instrument is used
that res ponds equally to noise of all frequencies within the audible rang e,
which is from 20 cis to 20000 cis approximately. This means that the
measuring instrument gives the same indication for all sounds of equal
physical "s trength" , whether the sound is of low, medium or high pitch.
When measuring noise containing several fr e quencies, th e wideband measurin~
instrument will deflect to a value which is proportional to the sum of e nergy
contents in all the different noise frequencies represented. See Fig. 2. This
type of measurement is used where it is desired to measure the overall
sound pressure level at a certain place. (S.P.L. in db is usually with ref e renc~
to the accepted hearing threshold: 0.0002 ,ubar).
1("5.
Frequency
Microphone
Fig. 2. Wideband measurement of noise. The meter will give an indication
which is slightly above the top of th e highest peak noted in the freque ncy
spectrum. Noise of all frequencies passes unattenuated to the meter.
b) "We ighted" Measurements.
We ighted measurements are m eas ur e ments taken with instruments which
have response curves that, to a certain deg ree , follow those of the human
ear. The human ear appears to be most sensitive to me dium frequencie-s and
is therefore not so irritated by low or high pitched noise. The frequen cy
response of "weighted" measuring instruments is then shaped in such a way
as to approximate the sensitivity curves of the human ear. This is normally
done by insertion of one or mor e filters in a wideband amp lifier. Three
differ e nt filter chara;teristics have been int e rnationally standardized for this
pllrpose .
• ) An instrument with a wideband response may also be referred to as one with a
response wbich is linear, overall, or lIat.
5

In the measurement of noise containing several frequencies , the instrument
measures the noise as the 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 level) and is stated in db
SL (= db de. 2 X 10-4 ,ubar), curve A, B or C.
Frequency
Microphone
Frequency Weighted
Level
c
o
:;:;
'-0
QJu
~'O
LE
Frequency
16 220 7
Fig. 3. Weighted measurements. As shown 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 pass unattenuated. That means that the medium
frequencies have a predominant influence on the meter indication.
c) Frequency Analysis of Noise.
Frequency 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 10
bands , each with the width of one octave; a 1 ,6 octave band analyzer divides
6

, Mi c rophone
Filter characteristic
:-"'J"r-
v--
..... (-y .... y-v-.,--
I I I I I II I \
I n 1\ I I 1\ /1 II ~I ~I \
,
,I \ J\ I 1 1I 1\ 1\ II 1I I
/ / \, I I, /I ' ' I I \ 1 \ \
/ I XI
I, 'V \I 1/ I \
/
Frequency
Naise bond Level
/
Filter ~ -- -- - -
I I
I \ §
I \ L.. :g
I \ !! . ~
/ \ OJ "0
L- __ -'- , _----' , _____ .. ::E S
Frequency
f62205
Fig. 4. Analysing noise by means of a series 01 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 deper.dant.
the range into 30 bands, each Ih octave wide. An example of such an
a nalyzer is the B & K Type 2112 mentioned on page 11. With an analyzer
of this typ e th e noise band level can be measured at any arbitrary frequen cy
without any disturbing influence from other (and pe rhaps "stronger ") sounds
ar riving at th e microphon e simultaneously. In this way it is possible to
investigate
which fr e qu encies are predominant, measur e their "strength" and
c haracter and thereb y a rrive at a method for treatment of the noise problem .
Bands narrow er than lh octave are not normally used in nois e measurements;
how ever, in th e inves tigation of vibration, an analyzer with filters having
a
width of less than lh octave would often be employed. The B & K Type
2107 is an example of such an analyzer .
d) Measurements in Seleeted Frequeney Bands.
Once laboratory investigations hav e been carried out upon objects from a
production lin e (or on the prototyp es) and th e noise and vibration generated
by the obj ects is analysed e.g. by means of an analyzer as me ntioned above,
it
can be calculated which of th e nois e frequencies must be checked in
production. Ofte n, atte ntion ma y be confined to certain important frequ encies
only,
and other bands ignor ed. A special instrum e nt which measures these
particular noise frequ encies (see Fig. 5) can then be used to check the units
7

from the production line. Such an instrument is the Noise Limit Indicator
Type 2211. It measures noise or vibration in a number of pre-selected
frequency bands simultaneously. The bandwidth can be chos en to be 1 octave
or lh octave, depending on the conditions.
, Microphone Filter. characteristics
lDJ0J\n.
Frequency c
.2
F ilt ers /
('iill[\ [I[!1
Frequency
162206
Fig. 5. This figure shows the measuring principle of the Noise Limit
Indicator. Several filters are inserted. The meter is substituted by red lamps,
so
that there is an indicator for e a c h filter. Thereby the excess of the
noise band limits
of several filters can be indicated simultaneously. The
;ilter attenuation can be adjusted for each filter individually.
The noise frequency bands and the levels set as the maximum limit for each
of
the bands selected should be chosen as a result of careful l aborato ry
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 capab le of checking a
number of pre-selected frequency band levels as well as the overall noise
level, both wideband and weighted, simultaneously.
CAPABILITIES 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 common ly used measurements that can be made
with the instrument are:-
8
1) Simple "go-no go" testing for noise or vibration or both simultaneously
(see Fig. 6a).

0
a)
0
0
0
Standard
0
b)
0
0
DO
D O
Extra Standard
0
0
c)
0
0
0 0 =
=
0 = 0 =
= =
E xtra Standard
0
00
d)
000
0000
0000
Closs 1 2 3
Noise
Limit
Indicator 0
Rejects
Noise
Limit
Indicator
Noise
Limit
Indicator
Noise
Limit
D
0
Rejects
t622()f
D§
Rejects
Indicator 0
Rejects
(62200
Fig. 6. Different measuring possibilities with the Noise Limit Indicator.
a) Simple testing dividing the objects from a production line in "rejects"
and "standards" with respect to noise and vibration.
b)
Same as a), but additionally dividing the approved objects in two classes,
"standard" and "extra".
c) If only one check of the noise or vibration of a unit is required, the two
inputs
of the instrument may be used to serve two production lines or two
kinds of products on a line, e.g. two types of motors, each with its own
noise frequencies
and limits.
d) When investigating the noise or vibration level of a series of units, the
instrument may be used to divide the units in 3, 4 or 5 classes as regards
noise or vibration.
9