BRUEL & KJAER 2206 - Page 9

2208 is used for viQration measure-
ment , the weighting network will
influence the readings making accu-
rate calibration extremely difficult.
Nevertheless, the accuracy is suffi-
cient for quick estimates of vibra-
tion level.
Two attenuator stages are pro-
vided, and these are connected to-
gether so that the 1 0 dB steps in
range are obtained with the best
possible signal to noise ratio. To
simplify readout, the range selected
is displayed in a window on the me-
ter scale . On the 2206 a separate
push-button switch operates in the
first amplifier stage. This can be
used
to increase the measuring
range quickly by 10 dB, regardless
of range setting, to allow for sud-
den high levels. The range control
switch on both instruments can be
locked internally , in any of its ten
positions (30 to 120 dB), to prevent
inadvertent range changes when
the instrument is to be used by in -
experienced personnel . The use of
the "+ 10dB" button is retained
while the range selector is locked.
Type 2206 is equipped with the
A and C-weighting networks and
has, in addition, a linear position.
The 2208, being equipped with a
maximum hold circuit, has only the
widely used A-weighting network.
The network selector switch can
also be locked to prevent accidental
changes which could cause false
readings. The A and C-weighting
characteristics are shown in fig . 3.
The second amplifier stage feeds
the rectifier and an AC output termi-
nal. The output is used with Tape
Recorders
or Level Recorders. (See
Fig.4) .
The rectifier gives correct RMS
values within 5% for signals with
crest factors up to 3 at full scale me-
ter deflection . The internationally
standardized "Fast" and "Slow " me -
ter damping characteristics are pro-
vided. The meter is a DC moving
coil instrument with ribbon suspen-
sion . The angled meter scale is eas-
ily read, with graduations from
-1 0 dB to + 1 0 dB over a 5, 5 em
(2,25 in) scale length .
In
the Type 2208, a special cir-
cuit can hold the maximum meter
deflection that occurs during a
measurement. This feature is partic-
ularly useful for measurements of
rapidly changing levels such as traf -
Bruel & Kj mr Bruel & Kjmr Bru el & Kjaer
oo ooooooooo o ooooooooooooooooooooooooooooooooooooo
ruei&Kjcer Potenti om e te r Rang e: -- dB Re ctif ier: - - Low er Lim Fr e q. :- Hz Wr Sp eed :- mm / s ec Pape rSpeed :- mm / sec.
Cop e nhag en 50 25 10 75
+
dB dB
dB dB
40 20
8 60
M e asur i ng Ob j .: f== f:= C
--- 3015
6 45
- -- 2010
4 30
10 dB
-- - 10
2 15
R ec . No .:
Dat e __ = f:= A
Sign .: __ 0 0
10 20 Hz 50 100
200 500 1 000 2000
Qp 11 24
M ul ti pl y Fre qu en cy Sca le by
Zero Level:
Fig.3. Typical A and C-weighting characteristics
74 0634
Miniature Sound
Level
Meter
2206 or 2208
Level
Recorder 2306
Fig.4. Portable set-up for recording
levels
fie noise. When the METER RESET
button is depressed the meter de-
flection is cleared, and the instru-
ment is ready for the next measure -
ment. In addition , a held level can
be
stored, to prevent loss of the
reading if subsequently a higher lev-
el
occurs . This is achieved by turn-
ing the Function Selector to
"Store", which grounds the incom-
ing signal to prevent it from reach-
ing the meter . The hold circuit can
be by-passed
allowing the Type
2208 to be used as a general pur-
pose sound level meter.
Another version, the Precision
Sound Level Meter Type 5606 is
available on special order for vehi-
cle noise measurements to ISO
R 362 (moving vehicles) and the pro-
posed ISO method for noise meas-
urements on stationary vehicles.
+ 1
dB
0
- 1
c
- 2
0
· ;;
Deflection in
Similar to a Type 2208 with a Con-
denser Microphone, the Type 5606
features a speical max . hold circuit
that can be externally controlled.
This enables a tachometer to trigger
the hold function when a preset en-
gine speed is reached .
The curves in Fig. 5 show the rela-
tive meter deflections to be ex-
pected
on the 2208 in position
"Fast" with MAX. RMS HOLD
switched to "On" and "Off" for dif -
ferent impulse durations. The dot-
ted line indicates that in position
"fast", HOLD "Off'' , the meter de-
flection will return to the real value
for a steady state signal with dura-
tion longer than about 1 second.
The overshoot in position "Fast",
Hold "Off" is as specified by IEC
R 179.
Calibration may be performed
with either the Type 4230 Sound
Level Calibrator (94 dB at 1000Hz).
or with the Type 4220 Pistonphone
( 1 24 dB at 250Hz) . Because the
2208 sound level meter registers
the . weighted sound level, a correc-
tion factor must be applied when
using the Pistonphone with this in -
strument .
------
- ........ ._
~-----
~
~
./
~
- 3
't
-4
pos . " Fast", Hold " on" ,
~
0
Q)
- 5
~
- 6
~
- 7
· ~
-8
Q;
a:
- 9
-10
- 11
- 12
- 13
- 14
~v
//
/A
//
"
//
Ma x. deflection in pos . "Fa st ", Hold "off"
//
//
//
/V
//
ff'
20
50 100
200 500
msec .
1
sec .
171007
Impulse Duration
Fig.5 . The relationship between Impulse Duration and Relative Meter Deflection for the 2208
3