BRUEL & KJAER 2212 User guide
Noise Limit Indicator Type 2212
Type
2212
Noise
Limit
Indicator
is
an
instrument
containing
six
identica
I
input
amp
I
ifiers
and
six
output
amplifiers
and
a
control
panel.
It is
mainly
intended
for
traffic
noise
monitoring,
f.
inst
.
at
airports
or
in
road
traffic
surveys.
BHUEL
&
KJJER
Naerum, Denmark .
~
80
05 00 .
~
BRUKJA,
Copenhagen
.
Telex:
5316
B B
2212
Noise Limit Indicator.
Type 2212
November
1966
Contents
1.
Description
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
General
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Input
Amplifiers
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Filters
and
Output
Amplifiers
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Overall
Frequertcy
Characteristic
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Rectifier
and
Relay
Circuit
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Control
Panel
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Meter
Circuit
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Power
Supply
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.
Identification
of
Control
Knobs,
Terminals,
etc
•.
.
.....
..
...........
10
3.
Operation
of
the
Noise
Limit
Indicator
Type
2212
as
Traffic
Noise
Monitor
.......
.....
................................
.
..........
..
12
General
.
......................................................
. .
12
Preadjustment
of
Noise
Limit
Indicator
Type
2212
..................
13
Connection
between
Noise
Limit
Indicator
Type
2212
and
Outdoor
Microphone
System
Type
4920 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Adjustment
of
the
complete
Measuring
Set-up
. . . . . . . . . . . . . . . . . . . . . . 18
Checking
by
means
of
the
Pistonphone
Type
4220 . . . . . . . . . . . . . . . . . . 20
Adjustment
of
the
Sensitivity
Increase
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
4.
Specifications
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2'2
1.
Description
General.
The
Noise
Limit
Indicator
Type
2212 is a
modified
version
of
the
well-known
Noise
Limit
Indicator
Type
2211
mainly
intended
for
traffic
noise
monitoring.
It
contains
six
identical,
separate
input
amplifiers
and
six
output
amplifiers.
Furthermore
two
"sets"
of
six
microphones
each
(
or
six
vibration
pick-ups)
can
be
successively
switched
to
the
input
amplifiers
by
means
of
a
remotely
controlled
relay
circuit.
It
is
thus
possible
to
quickly
check
12
measuring
positions-and
continuously
monitor
six.
The
input
circuit
of
the
amplifiers
c
ontains
a
transformer
which
allows
con-
nection
to
a
symmetrical
transmi
s
sion
system.
The
input
transformer
has
been
included,
however,
not
only
to
allow
connection
to
a
symmetrical
transmission
system
but
also
to
facilitate
the
remote
control
of
the
calibra-
tion
oscillator
in
a
connected
Outdoor
Microphone
System
Type
4920
over
a
two-wire
system
.
In
the
output
amplifiers
provision
is
made
for
the
insertion
of
filters.
The
Noise
Limit
Indicator
consists
of
the
following
major
parts.
1.
Input
Amplifiers.
2.
Filters
and
Output
Amplifier
s.
3.
Rectifier
and
Relay
circuits.
4.
Control
Panel.
5.
Meter
Circuit.
6.
Power
Supply.
Input Amplifiers.
The
Type
2212
contains
six
input
amplifiers
which
are
identical
and
interchangeable.
Each
of
them
contains
a
four-stage
transistor
amplifier
preceded
by
a 60
dB
attenuator.
The
attenuator
can
be
varied
in
10 dB
steps
and
is
intended
to
be
used
in
conjunction
with
the
48 dB
attenuator
in
the
output
amplifier.
The
first
amplifier
stage
is
designed
as
an
emitter
follower
in
order
to
obtain
a
sufficiently
high
input
impedance.
The
input
impedance
is,
for
the
least
sensitive
position
of
the
attenuator,
approximately
1.5 Mohms.
For
the
next
position
it
is
approximately
o.5
Mohms,
and
for
the
remaining
positions
150
kohms.
The
next
two
stages
are
RC-coupled,
while
the
last
stage
contains
two
transistors
in
a
single-ended
push-pull
arrangement.
The
output
signal
is
fed
via
a
relay
to
the
input
of
the
filters
in
the
output
3
n
n
4.
I
5.
:
6.
1
L
_________
J
4.
5.
I
6.
I
L----------------------
--
-J
When
the
pushbutton marked RELEASE is operated
the
lamps are reset
ond
INPUT
I or
INPUTn
disconnectod.
r
I
I
I
0 0
0 0 0
I I
I Meter
circuit
I
L
________
j
162.?76
Fig. 1.1.
Block
diagram
of
the
Noise
Limit
Indicator.
amplifiers.
The
relay
is
controlled
from
the
INP
UT I
or
INPUT
II
buttons
on
the
Control
Panel
and
serves
to
break
or
connect
the
input
circuits
to
the
filter
inputs
.
See
Fig.
1.1.
To
obtain
a
high
degree
of
stability
and
to
ensure
a
distortion
of
less
than
o.1
%,
a
large
amount
of
negative
feedback
is
introduced
in
the
amplifier.
The
feedback
can
be
altered
with
a
potentio-
meter
to
obtain
fine
adjustment
of
the
sensitivity.
A
second
potentiometer
can
be
switched
into
the
feedback
circuit
by
means
of
a
relay
which
is
controlled
from
the
SENSITIVITY
INCREASE
knob
on
the
control
panel.
This
potentiometer
can
be
set
to
increase
the
sensitivity
by
between
0
and
5 dB,
without
influencing
the
frequency
response
of
the
amplifier.
The
total
amplification
with
increased
sensitivity
is 45 dB.
Filters
and
Output Amplifiers.
Weighting
networks
or
filters
can
be
used
in
conjunction
with
the
Output
Amplifiers.
The
filters
can
be
by-passed
by
a
toggle
switch
on
the
front
plate
of
the
amplifier.
After
filtering,
the
signal
is
fed
to
a 48 dB
attenuator
with
1
dB
steps.
Two
independent
tappings
of
this
attenuator
make
it
possible
to
adjust
the
attenuation
to
two
different
settings,
one
for
each
of
the
two
inputs.
The
pushbutton
switches
on
the
control
panel,
which
are
used
to
select
the
desired
input,
also
select
the
correct
section
of
this
attenuator
(
with
the
aid
of
a
relay),
so
that
INPUT
I
corresponds
to
attenuator
tap
No. 1
and
INPUT
II
with
attenuator
tap
No. 2 (see
Fig.
1.3
and
block
diagram).
4
+1
db
01-"
-1
-2
-3
-4
-51
2 5
10
2 5
100
2 5 1000 2 5 10000 2
C/5
5 100000
Frequency
1'
2289
Fig. 1.2.
Frequency
Response
of
Input
Amplifier
without
input
transformer.
The
first
stage
of
the
amplifier
is
designed
as
an
emitter
follower
in
order
to
obtain
an
input
impedance
high
enough
to
have
no
influence
on
the
attenuator.
The
impedance
loading
the
filter
is
thus
determined
by
the
attenuator
and
is
approximately
146
kohms
which
gives
optimum
performance
of
the
filter.
The
following
stages
are
RC-coupled
amplifier
stages,
stabilized
by
negative
feedback.
Three
feedback
circuits
are
employed,
two
of
which
are
used
to
shape
the
frequency
response
curve
and
to
minimize
the
input
capacity.
The
third
one
can
be
varied
so
as
to
alter
the
amount
of
am-
plification
(
this
is
the
sensitivity
adjustment
on
the
front
plate
of
the
amplifier).
Control Panel
r n
,Q.QOOO
/
>(
'
II
To
Output
Amplifier 1
To
Output
Amplifier 2
~66H4-
Fig. 1.3.
By
depressing
one
of
the
INPUT
buttons,
the
correct
input
and
also
the
correct
tapping
of
the
INDICATOR
LEVEL
attenuators
are chosen
by
means
of
relay
circuits.
5
+
d
1
~
1/
.
2
...
~
I
5
I-I-
-
....
""
2 5
10
5
100
5
1000
2 5
10
K
C/5
5
100
K
162177
Fig. 1.4.
Frequency
Response
of
output
amplifier.
Overall Frequency Characteristic:
The
overall
frequency
response
of
the
instrument
(
without
filters
in
the
output
amplifiers
) is
shown
in
Fig.
1.5
and
is
mainly
determined
by
the
input
transformer.
Also a
loss
in
amplification
of
approximately
1
dB
takes
place
in
this
transformer.
The
curves
shown
in
Fig.
1.5
are
valid
for
various
generator
impedances,
R1.
To
allow
a
clear
picture
of
the
change
in
characteristic
with
generator
im-
pedance
and
voltage,
however,
the
curves
are
drawn
with
a
fictive
distance
between
the
flat
parts
of
2 dB.
l I
Rg=
60..n.
I
600mV
v-
I.
_I
:10mV
60mV
60
6mV
6mV Rg=200.n.
600mV7
~""""""
l
_I
\\
60mV Rg=600.n.
60-
soo~n~
6mV
~
6mV~
6mV-
600mV -;?
60mV I
2!8
Olrmv
r---
6mV i
t
10
20 50
100
200 500 1000 2
000
5 000
10
000 20 000 50000
100
000
Frequency Hz(cfs)
Fig. 1.5.
Frequency
chamcteristic
for
the
entire
instrument.
Rectifier and Relay Circuit.
Following
the
amplifier
is a
quasi-RMS
rectifier
circuit.
It
provides
full-wave
rectification
and
gives
accurate
RMS
indication
for
sinusoidal
signals
as
well
as
for
white
noise
and
other
signals
with
complex
waveforms,
including
asymmetrical
pulses
with
crest
factors
up
to
3.
By
means
of
a
switch
6
'
two
different
damping
characteristics
can
be
introduced
.
"Standard"
or
"low
damping"
is
meant
for
the
measurement
of
steady
signals
with
frequencies
above
20
Hz
while
"high
damping"
is
meant
for
the
measurement
of
fluctuating
signals,
i.e.
frequencies
below
20
Hz
or
measurements
where
fluctuating
background
noise
would
otherwise
disturb
the
meter
reading.
The
signal
is
now
capable
of
energizing
the
relay
which
makes
the
indicator
lamp
light-up.
This
relay
has
two
stable
positions.
However,
as
even
the
best
relays
do
not
always
operate
on
precisely
the
same
amount
of
current-flow,
another
stage
has
been
added
so
that
the
relay
invariably
switches
over
at
a
certain
input
signal
voltage.
This
stage
has
a
characteristic
as
shown
in
Fig. 1.6,
and
as
seen
the
steep
slope
of
the
curve
provides
a
large
current
increase
for
a
slight
voltage
increase,
thus
making
the
energizing
point
much
more
consistent.
To
obtain
a
stable
working
point
for
this
stage
a
zener-diode
is
introduced,
and
also
a 20
kHz
signal
is
presented
to
give
an
independent
bias
voltage.
This
signal
is
derived
from
a 20
kHz
generator
located
in
the
power
supply
unit
and
thus
common
for
all
the
amplifiers.
This
bias
is
so
adjusted
as
to
make
the
relays
operate
at
an
AC
input
voltage
of
2.24
V.
·
when
none
of
the
INPUT
buttons
on
the
Control
Panel
are
depressed,
the
relays
are
held
in
their
passive
position
by
means
of
a
"
holding
voltage"
of
approximately
12 V DC.
Before
\
the
rectifier
circuit
is
an
AC
output
lead
to
a
multisocket
on
the
rear
panel
of
the
instrument.
The
output
impedance
at
the
pins
of
this
I Output
Relay {
Current
Tolerance
2.
24
v
Voltage
tolerance
--j~b
Einput
162212
Fig. 1.6. Ei/1.
characteristic
of
the
current
shaping
stage
just
before
the
relay.
socket
is
approximately
25
ohms
(to
ground).
The
maximum
voltage
to
be
obtained
is
approximately
7
Volts
AC
(RMS). A
voltage
of
2.24 Volts
AC
at
this
point
energizes
the
relay.
7
Control Panel.
The
control
panel
contains
the
five
pushbuttons
intended
to
be
used
by
the
operator,
as
well
as
the
indicating
lamps
for
each
channel.
The
two
input
selectors
bring
the
proper
input
into
circuit
and
also
keep
the
relays
of
the
output
amplifier
in
the
passive
position
when
not
depressed.
The
SENSITIVITY
INCREASE
button
controls
the
relays
which
influence
the
amount
of
feedback
round
the
input
amplifiers,
thereby
increasing
the
sensitivity.
This
button
only
functions
while
kept
depressed.
The
RELEASE
button
releases
the
other
pushbuttons
and
thus
resets
the
"holding"
voltage
used
to
keep
the
relays
of
the
output
amplifiers
in
the
passive
position.
Furthermore,
the
RELEASE
button
serves
to
check
the
proper
functioning
of
the
output
relays
and
the
indicator
lamps,
as
all
the
lamps
are
lit
up
when
the
switch
is
pressed
down.
The
INPUT
I,
INPUT
II
and
RELEASE
buttons
operate
via
a
relay.
The
two
INPUT
buttons
are
furthermore
delayed
in
operation,
so
that
the
"holding
voltage"
used
to
keep
the
output
relays
in
their
passive
position
is
not
switched
off
till
approximately
1
second
after
the
input
amplifiers
are
switched
in.
It
this
way
the
disturbing
effect
of
transients
are
avoided.
A
green
light
indicates
when
the
instrument
is
operating
and
at
which
input
channel.
Parallel
to
the
RELEASE
button
is a
springloaded
RESET
button
which
serves
to
momentarily
reset
the
output
relays
to
their
passive
positions
without
releasing
the
INPUT
or
SENSITIVITY
INCREASE
buttons.
Its
purpose
is
to
recheck
the
lamp
indication
in
case
of
unwanted
noise,
e.g.
footsteps,
doors
slamming
etc.
Each
of
the
red
lamps
is
permanently
connected
to
a 12 V
AC
source
and
is
grounded
through
its
corresponding
output
relay.
In
this
way
the
lamps
cannot
be
lit
when
no
amplifier
is
inserted.
There
is a
relay
in
parallel
with
the
lamps.
The
relay
contacts
change
over
whenever
anyone
of
the
lamps
light-up.
The
switch
so
obtained
is
connected
to
pin
"T"
and
"U"
of
the
remote
control
plug
and
may
be
used
to
remotely
control
buzzers,
alarm
bells,
or
other
auxiliary
equipment.
Meter Circuit.
The
meter
circuit
of
the
apparatus
serves
mainly
as
an
aid
in
the
proper
setting
of
the
attenuators
and
to
check
amplification
by
means
of
the
built
-
in
reference
voltage.
The
meter
can
be
connected
through
a
switch
to
any
of
the
outputs
of
the
amplifiers
so
as
to
read
the
output
level
before
rectification.
The
rectifier
circuit
of
the
meter
is
identical
to
that
of
the
output
amplifiers,
as
is
the
damping
circuit.
To
provide
aural
or
visual
indication
of
the
signal
that
reaches
the
meter
circuit,
two
test
sockets
are
placed
beneath
the
meter.
These
sockets
are
in
parallel
with
the
meter
circuit,
allowing
headphones
,
oscilloscopes
or
other
instruments
to
be
connected
to
them.
8
Power
Supply.
The
power
supply
is
contained
in
one
unit,
the
Power
Unit
ZG
0001.
It
can
be
operated
from
power
lines
with
AC
voltages
of
100-115-127-150-220
or
240
Volts
and
frequencies
from
50
to
400
Hz.
Electrically
the
power
unit
can
be
divided
into
four
main
circuits:
(a)
the
25 V
supply,
(b)
the
20
kHz
supply
voltage,
(c)
the
reference
supply,
and
(d)
the
supply
for
lamps
and
control
panel
relays.
The
25 V
circuit
provides
25
Volts
negative,
for
use
as
the
collector
voltage
throughout
the
apparatus.
This
supply
is
accurately
controlled
by
a
voltage
regulator
circuit
containing
three
transistors,
ensuring
minimum
ripple
and
high
stability.
The
20
kHz
oscillator
produces
a
supply
voltage
for
the
final
stages
of
the
output
amplifiers.
It
is
designed
in
such
a
way
that
it
is
cut-off
when
a
voltage
of
approximately
12
Volts
is
applied
to
the
base
of
one
of
the
transistors.
By
means
of
the
relay
voltage
this
oscillator
is
cut-off
every
time
the
relays
are
set
to
their
passive
positions,
i.e.
when
none
of
the
INPUT
buttons
on
the
control
panel
are
depressed.
The
reference
voltage
is a 10
mV
signal
of
line
frequency
for
checking
the
amplification.
It
is
kept
constant
by
a
zener
diode
and
is
applied
to
the
input
of
the
input
amplifiers,
when
the
input
attenuator
is
set
to
the
"Ref"
position.
The
reference
voltage
varies
by
less
than
o.2 %
for
a 10 %
variation
in
mains
voltage.
9
2.
Identification of Control
Knobs,
Terminals
etc.
Meter Damping
Meter Switch
Normal Sensitivity
2
212
Indication Level
land
n
Filter
-Lin.
..-----Damping
~---Sensitivity
/66/(5
Fig. 2.1.
Front
view
of
Noise
Limit
Indicator.
Front Plate.
METER
DAMPING:
OUTPUT:
10
Four
positions
for
selection
of
meter
indicating
properties.
"Slow"
gives
the
highest
damping
of
the
indicating
meter
deflection.
"Off"
disconnects
the
meter
circuit.
"Fast"
gives
the
smallest
damping.
"Micr.
Ref."
in
connection
with
the
proper
setting
of
the
METER
SWITCH
serves
to
check
the
correct
setting
of
the
"Ampl.
Sens."
of
the
microphone
amplifier.
Output
terminals
from
the
output
amplifier
in-
dicated
by
the
METER
SWITCH.
METER
SWITCH:
INPUT
LEVEL:
SENSITIVITY
INCREASE:
Selection
of
indication
on
the
meter
of
the
output
from
one
of
the
sets
of
built-in
amplifiers.
Input
attenuator
for
adjustment
of
the
input
level
in
steps
of
10 dB.
In
the
position
"Ref."
it
is
pos-
sible
to
check
amplification
by
means
of
the
built-
in
reference
voltage.
Screwdriver
operated
potentiometer,
which
can
be
preset
in
the
range
0
to
5 dB.
SENSITIVITY
IN-
CREASE
is
activated
by pressing
the
corresponding
button
on
the
Control
Panel
ZH
0002.
NORMAL
SENSITIVITY:
Screwdriver
operated
potentiometer
for
adjustment
of
sensitivity.
Normally
adjusted
when
delivered
from
the
factory.
FUSE,
SUPPLY
VOLTAGE:
FUSE:
POWER:
INDICATION
LEVEL
I AND
II:
FILTER,
LIN:
DAMPING:
SENSITIVITY:
Rear
of
Apparatus.
INPUT
1:
INPUT
II:
CONTROL
PANEL:
AC
OUTPUT:
Fuse
in
circuit
with
primary
of
mains
transformer.
Voltage
selector,
for
setting
apparatus
to
various
mains
voltage.
Fuse
in
the
regulated
circuit
for
collector
voltage
and
filament
voltage
supply.
For
switching
the
power
on
and
off.
Step
attenuators,
1 dB
steps,
the
black
knob
for
"
Input
I"
and
the
transparent
knob
for
"Input
II".
For
setting
the
indication
level
in
connection
with
the
INPUT
LEVEL
knob.
Toggle
Switch
for
switching
between
linear
fre-
quency
response
and
interchangeable
filters.
Screwdriver
operated
switch.
Position
"Low"
for
measurement
of
steady
signals
with
frequencies
above
20
Hz.
Position
"High"
for
measurements
of
fluctuating
signals
of
frequencies
below
20
Hz.
Screwdriver
operated
potentiometer
for
adjustment
of
sensitivity.
Normally
adjusted
when
delivered
from
the
factory.
Connections
for
6
microphone-amplifier
systems
.
Connections
for
6
microphone-amplifier
systems.
Note:
Ensure
proper
connection,
see
page
17.
For
connection
to
the
control
panel
by
means
of
the
multicored
cable
supplied
with
the
instrument.
Direct
AC
output
from
the
six
output
amplifiers.
11
3.
Operation of the Noise
Limit
Indicator
Type
2212
as
Traffic
Noise Monitor
General.
The
signal
which
is
fed
to
the
input
circuit
of
the
Noise
Limit
Indicator
Type
22'12,
will
normally
be
delivered
from
a
microphone.
When
using
a
B & K
microphone
cartridge
and
cathode
follower,
it
is
then
necessary
to
employ
a
microphone
power
supply
for
instance
the
Microphone
Power
Supply
Type
2801.
However,
for
field
measurements
(airport
noise,
traffic
noise,
etc.)
it
is
recommended
to
use
the
Outdoor
Microphone
System
Type
4920
instead
of
Type
2801
as
this
equipment
contains
not
only
the
necessary
power
supply,
but
also
a
calibration
oscillator,
a
rain
cover
with
built-in
electro-
static
actuator,
a
microphone
cartridge
with
cathode
follower,
a
windscreen
and
an
amplifier.
The
calibration
oscillator
can
be
switched
in
by
means
of
a
knob
on
the
2212.
Windscreen UA0082
Rain
Cover
UA
0056
/Microphone
Cartridge
4133
Co
thode Follower
10m
'------.
min
.2
conductor
Main
Unit
in the
Control Tower
I
Distance
up
:
to
10
km
cable
2212
Microphone
system
in the field
Noise
Limit
Indicator
ft.W5"
Fig. 3.1.
Measuring
set-up
consisting
of
the
Noise
Limit
Indicator
Type
2212
and
the
Outdoor
Microphone
System
Type
4920.
12
Furthermore,
the
output
from
the
amplifier
in
the
4920,
can
be
connected
to
a
cable
and
transmitted
over
a
distance
of
up
to
10
km
before
connection
is
made
to
the
Noise
Limit
Indicator.
To
obtain
the
best
signal
to
noise
ratio
for
transmission
over
long
distance,
it
will
be
necessary
to
adjust
the
amplification
of
the
signal
in
the
Microphone
System
Type
4920,
in
such
a
way,
that
the
output
voltage
from
4920
will
be
about
1
volt
RMS
for
the
highest
sound
pressure level
limit
,
that
has
been
preset
on
the
Noise
Limit
Indicator
Type
2212.
When
using
a
transmission
cable
which
picks
up
a
minimum
of
noise
and
the
measured
sound
pressure
level
is
in
the
range
from
90
dB
to 120 dB,
the
amplification
can
be
adjusted
so
that
the
90 dB
SPL
from
the
electrostatic
actuator
in
the
rain
cover
,
can
be
read
off
directly
on
the
indicating
meter
of
Type
221'2 *).
Before
making
any
adjustment
to
the
Outdoor
Microphone
System
Type
4:920,
the
Noise
Limit
Indicator
Type
2212
must
be
pre-adjusted,
and
it
is
also
necessary
to
determine
the
noise
levels
to
be
tolerated
at
the
various
measuring
places
and
decide
which
kind
of
filters
or
weighting
networks
are
to
be
used
in
the
output
amplifiers.
When
these
have
been
decided
upon
,
the
instrument
can
be
adjusted.
The
adjustment
should
be
made
by
some-
one
who
has
a
fundamental
idea
of
electrical
circuits
or of
noise
measurements
in
general.
It
should
preferably
be
carried
out
in
accordance
with
the
following
procedure.
Pre-adjustment
of
Noise
Limit
Indicator
Type
2212.
1.
Connect
the
Control
Panel
ZH
0002
to
the
main
chassis
via
the
multicore
cable,
the
power
cable
to
the
power
line
and
switch
on.
2.
The
filters
are
now
chosen
in
accordance
with
the
requirements.
The
following
filters
can
be
supplied:
ZS 0240
WEIGHTING
NETWORKS,
containing
the
"A",
"B"
and
"C"
networks
together
with
a
linear
response
20-
35ooo
Hz.
ZS 0250
FILTER
SET
containing
33
third-octave
filters
with
center
frequencies
of
12.5 -16 -20
......
20ooo
Hz.
The
11
filters
with
center
frequencies
of
16 -31.5
-·
63
......
16ooo
Hz
can
be
switched
to
a
width
of
1/1
octave,
maintaining
their
center
frequencies.
ZS 0251 OCTAVE
FILTER
SET
containing
the
above
mentioned
11
switchable
filters.
ZS 0234 1/3 OCTAVE
FILTER.
Center
frequency
25
kHz.
ZS 029'5 1/3 AND 1/1
OCTAVE
SWITCH
ABLE
FILTER.
Center
frequency
31.5
kHz.
ZS 02'
36
1/3
OCTAVE
FILTER.
Center
frequency
40
kHz
.
*)
If
the
measured
sound
pressure
level is
in
the
range
from
60
dB to
90
dB,
the
amplification
of
the
4920
should
be
increased
by
10 dB
and
that
of
the
2212
decre
a
sed
by 10 dB.
Then
when
the
signal
level is
read
off
directly
on
the
Noise
Limit
Indicator
,
it
must
be
remenbered
that
it
gives a
10
dB
higher
level
than
the
real
signal
level.
13
162283
Fig. 3.2.
An
Output
Amplifier
withdrawn
from
the chassis.
The
screws
intended
for
fastening
the
filter chassis are indicated at
the
rear.
3.
The
filters
are
placed
in
the
six
output
amplifiers
as
described
below:
a)
Loosen
the
output
amplifier
unit
from
the
main
chassis
by
un-
screwing
the
knurled
nut
at
the
bottom
of
each
amplifier
unit
front
plate.
b)
Pull
out
the
amplifier
unit.
c)
Loosen
the
screws
on
the
rear
of
the
amplifier.
(See
Fig
. 3.2).
Fig. 3.3.
The
Output
Amplifier
mounted
with
filter chassis,
ready
to insert. ·
14
!62285'
Insert
Paper-tag
Fig. 3.4.
The
paper tag
from
the
filter is
inserted
in
the
slit
behind
the
window
as
shown.
d)
Remove
the
piece
of
paper
indicating
the
filter
frequency
from
be-
neath
the
filter
and
place
the
filter
on
the
amplifier
as
shown
in
Fig.
3.3.
e)
Re-tighten
the
screws
on
the
rear
in
order
to
fasten
the
filter
to
the
amplifier.
f)
Place
the
complete
unit
in
its
opening
in
the
chassis
and
tighten
the
knurled
nut
on
the
front
plate
.
g)
Place
the
piece
of
paper
indicating
the
filter
frequency
in
the
slit
under
the
window
on
the
front
plate
of
the
amplifier
,
thus
indicating
which
filter
is
inserted
(see
Fig
. 3.4-3.5).
0
Indicator Level
db
J-@-11
r~~:rl
@)
Lin.
Fig. 3.5.
15
4.
The
gain
of
all
the
amplifiers
used
should
now
be
checked
and,
if
necessary,
adjusted
as
follows:
Normally
the
screwdriver
operated
potentiometers
marked
NORMAL
SENSITIVITY
and
SENSITIVITY
on
the
input
and
output
amplifiers
are
adjusted
when
the
instrument
is
delivered
from
the
factory.
How-
ever,
to
check
the
adjustment
proceed
as
follows:
a)
Set
INPUT
LEVEL
knob
on
input
amplifier
1
to
its
"Ref."
position.
b)
Set
the
METER
DAMPING
knob
to
"Fast"
position.
c)
Set
METER
SWITCH
to
position
"1".
d)
Set
the
toggle
switch
on
the
output
amplifier
to
"Lin".
e)
Set
both
of
the
attenuator
knobs
on
the
front
plate
of
the
output
amplifier
1
to
their
0
positions
(fully
clockwise).
f)
Press
the
INPUT
1
button
on
the
Control
Panel.
The
pointer
of
the
indicating
meter
on
the
Noise
Limit
Indicator
Type
2212
should
now
deflect
to
the
red
mark
(0
dB) .
In
cases
of
small
diviations,
the
said
condition
can
be
obtained
by
adjustment
of
the
NORMAL
SENSITIVITY
potentiometer
on
the
input
amplifier
1.
If
the
instrument
is
completely
out
of
adjustment
the
following
must
be
carried
out.
g)
Pull
out
the
output
amplifier
1.
h)
Connect
an
AC
multimeter
between
pin
2
in
the
multisocket
and
chassis.
i)
Adjust
NORMAL
SENSITIVITY
on
input
amplifier
1
until
a
deflection
of
1
volt
AC
on
the
multimeter
is
obtained.
j)
Remove
the
multimeter
and
plug-in
the
output
amplifier
1.
k)
Adjust
the
SENSITIVITY
potentiometer
on
the
output
amplifier
in
such
a
way
that
the
pointer
of
the
indicating
meter
on
the
2212
deflects
to
the
red
mark.
I)
Repeat
items
a
to
k
for
amplifiers
no.
2-3-4
etc.
with
METER
SWITCH
in
position
2-3-4
respectively.
Now
the
Noise
Limit
Indicator
Type
2212 is
pre-adjusted
and
the
transmitting
cable
from
the
Outdoor
Microphone
System
Type
49
·20
can
be
connected
to
the
input
plug
1
on
the
rear
of
the
2212.
Connection
between
Noise
Limit
Indicator
Type
2212
and
Outdoor
Microphone
System
Type
4920.
As
the
input
of
Type
2212 is a
symmetrical
transformer
input
with
grounded
midpoint,
it
is
most
convenient
to
have
the
output
of
Type
4920
floating,
as
this
will
avoid
errors
due
to
ground
currents
and
possible
asymmetry.
See
Fig. 3.6.
It
is
possible
to
connect
twelve
492'0's
to
one
2212
even
though
the
Type
2212
is
only
equipped
with
six
sets
of
amplifiers.
At
the
rear
of
the
2212
there
are
two
inputs,
INPUT
I
and
INPUT
II,
16
4920
I
1--0
1 0Dir. outp.
I
iL
____
0
0sc
.
on
2212
t'66NZ
Fig. 3.6.
Wiring
up
the
connection
between
Type
4920
and
2212.
corresponding
to
the
two
switches
on
the
control
panel
ZH
0002
marked
INPUT
I
and
INPUT
II.
To
each
input
six
4920's
can
be
connected
as
follows:
Channel
1
to
A
and
B
2 » C D
3 » E F
4 » H J
5 » K L
6 » M N
Thus
by
switching
between
the
two
inputs,
each
set
of
six
49·20's is
alter-
nately
connected
to
the
six
amplifiers
in
Type
2212.
In
cases
where
less
than
twelve
4920's
are
required
it
is
possible
to
connect
s
ome
of
them
to
both
inputs.
As
an
example
of
this
application
Fig.
3.7
shows
a
set-up
where
eight
49·20's
are
connected
to
one
Noise
Limit
Indicator.
This
set-up
offers
the
facility
of
continuously
monitoring
the
four
4920's
con-
IB+liB
1
4
Input
I
Input
TI
f661f3
Fig. 3.7.
An
example
of
the
connection
of
eight
Type
4920's to
one
2212.
17
nected
to
both
inputs,
while
the
remaining
four
4920's,
divided
between
INPUT
I
and
INPUT
II,
will
be
monitored
alternately.
Adjustment
of
the
complete
Measuring
Set-up.
When
the
transmitting
cable
between
the
Microphone
System
and
the
Noise
Limit
Indicator
picks
up
a
minimum
of
noise
and
the
measured
signal
is
in
the
range
90-
120
dB
SPL,
the
adjustment
of
the
complete
measuring
set-up
will
be
as
follows:
The
Noise
Limit
Indicator.
1.
Set
METER
DAMPING
to
"Micr.
Ref.".
2.
Set
METER
SWITCH
to
position
"1".
3.
Set
INPUT
LEVEL
on
input
amplifier
1
to
"90".
4.
Set
both
of
the
attenuator
knobs
on
the
front
plate
of
the
output
amplifier
1
to
their
"0"
positions
(fully
clockwise).
5.
Set
the
toggle
switch
on
the
output
amplifier
1
to
"Lin".
6.
Press
the
INPUT
1
button
on
the
Control
Panel.
The
Outdoor
Microphone
System.
Connect
ihe
complete
Outdoor
Microphone
System
Type
4920
to
the
trans-
mission
cable
and
switch
on
the
power.
Because
of
the
90
dB
SPL
produced
by
the
electrostatic
actuator
inside
the
rain
cover
in
the
microphone
system,
the
pointer
of
the
indicating
meter
of
the
Noise
Limit
Indicator
Type
2212
will
deflect.
By
means
of
the
screwdriver
operated
potentiometer
marked
AMPL.
SENS.
on
the
printed
circuit
of
the
4920,
the
amplification
of
the
amplifier
is
adjusted
until
the
pointer
of
the
indicating
meter
of
the
2212
will
deflect
to
0
dB,
equal
to
the
red
mark
on
the
scale.
The
sound
pressure
level
of
90
dB
can
then
be
read
off
directly
on
the
Noise
Limit
Indicator
as
the
sum
of
the
value
on
the
INPUT
LEVEL
knob
plus
the
figure
on
the
INDICATOR
LEVEL
knob
on
the
output
amplifier
plus
the
indicated
level
on
the
meter.
The
complete
set-up
is
now
calibrated
to
measure
the
absolute
sound
pressure
level
of
a
sound,
and
the
next
adjustment
will
be
to
preset
the
levels,
for
the
various
measuring
places,
for
which
the
2212
should
give
indication.
Adjustment
can
be
carried
out
as
shown
in
the
following
example:
Micr.
poss.
Max.
level
dB
1
88
The
Noise
Limit
Indicator.
2
102 3
97
4
79
5
91
6
66
1.
Set
the
INPUT
LEVEL
knobs
on
the
input
amplifiers
to
the
nearest
position
higher
than
the
required
level.
2.
The
output
attenuators
(INDICA
TOR
LEVEL
1,
black
knobs)
are
set
as
to
obtain
the
desired
noise
limit
for
each
microphone
position
as
follows:
Attenuator
setting=
Noise
Limit
-
INPUT
LEVEL
setting.
18
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