BRUEL & KJAER 2222 - Page 9

nal levels of the amplifier and if an
overload occurs , the display shows
"• ". It disappears only when the in-
strument is reset. For Max. Hold
functions the lower limit of the mea-
suring range is 15 dB higher than for
the Leq range.
Leq Calculation
The Leq is calculated over a maxi-
mum period of 2, 77 hours which is
the limit of the time counter. After
this time, the display shows "*" to
indicate that the Leq value now dis-
played is incorrect. However, the
SEL value is not affected by this time
limitation as it is always calculated
using a time period of 1 second. A
conversion table on the reverse side
of the instrument gives the Leq over
any period from the SEL value and
the elapsed time.
Digital Display
Measurement values are shown on
a 3112 digit display , with a resolution
of 0,1 dB. It is updated every 112 sec-
ond for Leq and SEL measurements,
and every 1 second for Max. Hold
measurement. The following charac-
ters may also be displayed:
"A": A-weighted frequency response
"L": Linear (flat) frequency response
"* ": Maximum Leq measuring time
exceeded
"•": An overload has occured dur-
ing the measuring period
"~": The sound pressure level is un-
der the minimum range level
"BAT": Batteries must be changed.
"00.0": Initial display check
dB
+4
+2
'
.........
" - - - ": Underrange in Max. Hold
measurements and delay after Reset
Power Supply
Power is supplied from 3 alkaline
batteries (IEC R 20) which will pro-
vide approximately 10 hours of con-
tinuous operation .
_. I, .. ,, .. I I*
B~T' Lf 0. -,A
Fig.2. Display of Types 2221 and 2222
~ o l ~ r a~ce: I~C k51
.,..-
--
I I
ty pe 1
I
I
--
Max. Hold Fast/Slow and Max. o
...- .......
F ree -f ie ld response_
--
"'
"""\.
Hold Peak calculation
When Max. Hold is selected the
output signal from the log converter
is fed directly to the Max. Hold cir-
cuit if " Peak " is required, or via an
averaging circuit for Max . Hold
" Fast/Slow" measurements. The
output from the Max. Hold circuit is
fed via the antilog , integrator and
counte r circuits to the microproces-
sor which controls the 1 s updating
and display of the Max. Hold
readings.
Both instruments can be modified
to obtain Max. "Slow " instead of
Max. "Fast " and vice versa.
Pause
The Types 2221 and 2222 have a
" Pause " function which in the "L eq"
and "SEL" modes , interrupts the
measurement without resetting. This
can be used for example when the
instrument is moved from point to
point for spatial averaging of the
no ise from a sound source .
In Max . Hold modes the " Pause "
function freezes the display , but any
higher signal occuring while in
" Pause " will be displayed when com-
ing back to "Run ".
Reset
The instrument is reset either
automatically when changing be-
tween measuring ranges and func-
tions (except between L eq and SEL)
or manually by push button . The new
measurement begins 112 second later
to avoid measuring the switch noise.
"-,
"\
/
'-,
- 2
- 4
'\
10
20
100
200
1 k
2k
10 k
20 k
Frequency (H z)
8 11 3 11
Fig.3. Typical free field frequency response of the complete instrument with 0° incidence
shown as deviation from the standardized A-curve
dB
+4
~
+2
0
I---
- 2
./
- 4
10
.........
"'-
""'""""r-....
-.....,
./.,_v
....,......v
20
100 200
1 k 2 k
Frequency (Hz)
Tolerance: ANSI S 1.4 .- 1971
· -
V1
l Typ e 1A
...,...f.- 1--
I I I I
With Random
...
~ Incidence Ad a pt or
I\ Withou t Ra ndom
r\~
\l~c i den c e Adaptor
"
V\1
I I I
\I I
I I
10 k
20 k
8113 12
Fig.4. Typical diffuse field frequency response of the complete instrument shown as deviation
from the standardized A-curve.
Fig.5. Directional characteristics of the complete instrument
3