level)
is
more than
10
dB
lower
than
that
when
the
machine
is
operating,
then no correction for background noise
is
necessary.
When
the
difference between
"total"
noise
level
and background noise
level
is
between
about
10 and 3 dB an approximate correction may be made
by
consulting the chart shown
in
Fig.5.8.
If
the difference between
"total"
and background noise
level
is
less
than
3 dB, it
is
advisable
to
move
the
machine
to
a quieter place.
0>
7
c:
~
~
6
~
B
E 5
.g
N 4
~
.0
iil
3
Q)
..c
! 2
"'0
.....
0
l
\
\
~
\
\
\
'\
2 3
"
........
,
'~
..........
~loo.
-
r-
r--
~
4 5
6
7
8
9
10
dB
Difference between total reading
and
background reading
171139
Fig.
5.
8.
Correction
for
the influence
of
background noise
5.5. TEMPERATURE
The operating temperature range
of
the
microphone
is
-50
to
150°C
though there
is
a permanent sensitivity change when operated
at
high
temperatures for a
long
tim"
.
Fig.5.9. Sensitivity change
of
4145
with
temperature
57
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