EasyManua.ls Logo

BRUEL & KJAER 2204 - Amplifiers; Meter

BRUEL & KJAER 2204
72 pages
Print Icon
To Next Page IconTo Next Page
To Next Page IconTo Next Page
To Previous Page IconTo Previous Page
To Previous Page IconTo Previous Page
Loading...
technical
specification
and
an
individually
obtained
frequency
response
curve
as
shown
in
Fig.
5.1.
The
upper
curve
is
the
free
field
response
which
applies
when
the
microphone
is
used
for
ordinary
sound
level
measurements.
The
lower
curve,
which
is
the
pressure
response
of
the
microphone,
applies
for
measurements
in
small
closed
volumes
with
dimensions
so
small
that
essentially
no
wave
motion
takes
place,
as
for
example
a 6 cm3
coupler
for
earpbone
measurements.
To
ensure
high
operating
stability
under
varying
conditions
of
temperature
and
humidity
the
microphone
diaphragm
and
housing
are
made
of
materials
having
identical
temperature
coefficients
of
expansion,
and
the
back
plate
is insulated
from
the
housing
by
means
of
silicone
treated
quarts,
giving
the
highest
possible leakage resistance
in
areas
of
high
relative
humidity.
The
microphone
as
well
as
the
amplifiers
are
unaffected
by
humidity
as
long
as
no
condensation
takes place
within
the
instrument.
The
change
in
microphone
sensitivity
due
to
variations
in
ambient
pressure
and
temperature
can
be
seen
from
Figs. 5.2
and
5.3.
dB
~~:1==
II
I
I==N
I
1::::=1111:::::!
I !
1:::::11
~
-40
-20
0 20
40
60 80
100
120
140
160°C
-40 - 4 32
68
104 140
176
212 248
284
320°F
1619#1
Fig. 5.3. Variation
of
microphone
sensitivity
with
temperature
at
400 flz.
As
the
amplifier
and
meter
circuit
can
be
checked
by
means
of
an
internal
calibration
signal,
the
important
factor
is
the
stability
of
the
microphone,
and
as
shown
above,
the
microphone
is
almost
unaffected
by
environmental
con·
ditions.
The
Amplifiers.
The
amplifiers
are
insensitive
to
variations
in
temperature.
Within
the
range
15• to 45• C
the
amplification
does
not
vary
noticeably,
and
as
shown
in
Fig.
5.4
the
change
is less
than
± t dB
in
the
range
to•
to
60° C.
The extensive use
of
transistors
requires
that
the
instrument
should
not
be
subjected
to
more
than
75° C
for
long
periods
of
time,
although
it
will
stand
90° C
for
some
200
hours
without
damage
to
anything
but
the
batteries. Below
-:-to•
to
-t5
• C
the
instrument
becomes inoperative.
The
Meter.
The
meter
is
calibrated
at
a
temperature
of
about
20° C
but
may
show
a slight
variation
due
to
the
temperature
characteristic
of
the
diodes
in
the
rectifier
circuit.
This
variation
does
not,
however, exceed o.4 dB
in
the
temperature
range
of
normal
use.
28

Table of Contents

Related product manuals