BRUEL & KJAER 1617 - Page 8

Description
Both Band Pass Filters are de-
signed to operate on the signals ob-
tained from the External Filter termi-
nals of the Measuring Amplifiers ,
but any input signal of approxi-
mately 1 V RMS with a crest factor
less than 5 can be accepted (the
higher crest factor capability of the
Type 2606 can be used at lower sig-
nal levels). Input and output are via
coaxial B
& K sockets on the front
panel, paralled by BNC terminals on
the rear.
Filter I
Filter II
11 3 Octave
Centre Centre
Bandwidth
Frequency Frequency
at 3.7 dB
Hz
Hz
Hz
Approx .
2
0,46
2.5
0. 50
3. 15
0 . 73
4
0.92
5
1.
16
6.3
1,45
B
1.
83
10 2. 30
12.5
2. 90
16
3. 70
20
4.60
25
5.8
31 .5
7
.3
40
9.2
50
11 .6
63
14 .5
80
18 .3
100 23
125
29
160 37
200
46
250 58
315
73
400 92
500
116
630
145
800
183
1000
230
1250
290
1600 370
2000
460
2500
580
3150
730
4000 920
5000
1160
6300
1450
8000
1830
10000 2300
12500
2900
16000 3700
20000
4600
25000
5800
31500
7300
40000
Additional
9200
50000
1/ 3-octav e
11600
63000
filters
14500
80000
in 1617
18300
100000
23000
125000
29000
160000
37000
Table 2. Filter centre frequencies in pre-
ferred series . Heavy type denotes
preferred series for full-octaves
Input
Warning
Front
P anel'
Controls
Amplifier
Low Pass
F ilter
Output
Amplifi er
Digital . t::=+.;;
Controller t-
Ou tput
761039
Fig.l . Block diagram of the Band Pass Filters Type 1617 and Type 1618
Fig.1 is a block diagram valid for
both versions of Band Pass Filter,
where shaded areas represent fea-
tures found only in the Type 1617 .
Third-Octave Band Pass Filters
The active Filter sections consist
of a matched pair of variable fre-
quency six-pole Butterworth filters
which can be electronically
switched to yield third-octave or full -
octave bandwidths . Between them
the two Filters cover the frequency
range from 2 Hz to 20 kHz centre
frequencies , with each Filter being
switched to alternate third-octave
centre frequencies in the preferred
series (see Table 2).
In the Band Pass Filter Type
1617 there is an additional set of
third-octave Filters with centre fre-
quencies between 25 kHz and
160 kHz, to extend the high fre-
quency range of the instrument.
The filter characteristics of the in-
dividual third-octave Filters used in
these instruments fulfil the require-
ments of IEC 225 - 1966 , DIN
45652, and ANSI S 1. 11-1966
Class III, which are the most rigor-
o
I,
/, 1 ~
/: '.\
/ : 20 \\
/ I 1\
/,' 3 '. \
/ I I \
/ " \
/
" \
/ \ \
/ 50 \ \ IEC
/' I "
I
/
I
/
0.2 0,5
00
~ 60
.g
..
"
~ 70
<
75
2
\ ........
\
\
Typical B & K
1/3 Octave Filter
'. ANSI Class III
.lOIN 45652)
'--
4
Frequency
relative to centre frequency fl fm
110103
Fig.2 . Typical third - octave filter response
3