BRUEL & KJAER 1617 - Page 7

The Third-Octave and Octave
Band Pass Filters Type 1617 and
Type
1618 are key links in any in-
strumentation chain for measure-
ment and recording of the fre-
quency spectra of sound, vibration,
and electro-acoustic signals . Sev-
eral novel
features have been in-
corporated, including electronic fil-
ter switching and digital indication
of the selected filter . The Band Pass
Filter Type 1618 is the basic instru-
ment, while the Type 1617 com-
bines an extended frequency range
with comprehensive control and syn-
chronisation facilities for use with
other instruments.
The Type 1 61 8 has fi Iter band
centre frequencies from 2 Hz to
20 kHz that can be divided into 41
third-octave bands, or 41 overlap-
ping octave bands covering the 14
octave frequency range. It has a
built-in A-weighting network, and
there is indication given when the
level of the signal being analyzed
overloads
the input section. The
Band Pass Filter has provision for fil-
ter scanning controlled by B & K Le-
vel Recorders.
The Type
1617 has filter band
centre frequencies from 2 Hz to
160 kHz that can be divided into 50
third-octave bands. It has 41 over-
lapping octave bands covering 14
octaves from 2 Hz to 20 kHz. In addi-
tion to the A-weighting, it includes
B, C, and D-weighting networks,
and there is also an input overload
indicator lamp. Filter scanning can
be controlled by a Level Recorder,
and
there is a built-in interface to
the proposed IEC Digital Bus Stand-
ard to permit direct control by other
instruments and systems using this
standard. A DC ramp output can
control the X-axis of an X-V Recor-
der, and a control circuit is included
to select averaging time programs
for use by the measuring instru-
ment.
Both Band Pass Filters will gener-
ally be used with one of the Measur-
ing Amplifiers Type 2606, Type
2607, or Type 2608, but other in-
struments such as the Frequency
Analyzers Type 2120 and Type
2121 , or the Heterodyne Analyzer
Type 2010 can be employed . Con-
nected to a B & K Condenser M icro-
phone, these measuring instru-
ments all form a sound measure-
2
ment system that satisfies IEC 179
for precision sound level meters,
while Type 2606, Type 2607, and
Type
2120 satisfy IEC 179 A for Im-
pulse measurement .
sic
system of Type 1618 and Type
2608 is for RMS measurement in
the audio frequency range, with fil-
ter selection by Level Recorder. Opti-
mum utilisation of all measuring
modes and control possibilities is ob-
tained with a combination of Type
1617 and Type 2607, which gives
the ability to measure and analyze
in the frequency range from 2 Hz to
160 kHz, obtaining RMS and Peak
values from all commonly encoun-
tered random, quasi-random, peri-
odic, and complex waveforms . This
combination can be used together
with an X-V Recorder.
All three Measuring Amplifiers
can be employed with either Band
Pass Filter , so that selection of
which Measuring Amplifier to use
will largely depend on the particular
measurement application. Table 1
shows the various combinations
available, together with brief specifi-
cations, and the type of measure-
ment and analysis possible. The ba-
Measuring Amplifiers
Band Pass Filter Type 1618
Band Pass Filter Type 1617
General :
General: General:
Freq. Range: 2 Hz - 200 kHz Freq. Rang e: 1.4 Hz - 22 kHz Freq. Range: 1.4 Hz - 180 kHz
Dyn . Range: 1 OIN - 300V
41 third-oct. bands 50 third-oct. bands
Fast and Slow averaging
41
overlapping octave bands
41
overlapping octave bands
Input overload warning
A-weighting filter
- A, B, C, D-weighting filters
Averaging time programs
Control via built-in IEC interface
• DC ramp for X-V Recorder control
Type 2608 and 2121
RMS measurement
RMS measurement
Crest factors up to 5
20Hz - 22 kHz
20 Hz - 180 kHz
AC output to Level Recorders
(Audio frequencies)
A-weighting network
Manual or remote control of filter scanning
Digital bus control of filter
scanning
Measurements can be made at lower frequen cies if th e
averaging
ability of a Level Recorder 2307 is used
Type 2606 Comprehensive RMS measurement at high crest factors
RMS and Peak
measurement
Impulse and Hold modes
20Hz - 22 kHz 20Hz- 180kHz
Crest factors up to 40 (Audio frequencies)
AC or DC outputs to Recorders
A , B, C, D-weighting networks
Manual or remote control of filter scanning
Range settings shown on
Digital bus control of filt er
meter scale
scanning
Measurement in Peak or Impulse Modes
1.4 Hz - 22 kHz 1.4 Hz - 1 80 kHz
RMS measu
rement s ca n be made at l ower fre quencies if th e
averaging ability of a Level Recorder 2307 is used
Type 2010 (RMS only) ,
Measurement of RMS and Peak values of all commonly encount- I
2607, & 2120
ered random . quasi- random . periodic. and complex waveforms
RMS and Peak measurement
Impulse and Hold modes
1.4 Hz - '22 kHz
1
.4 Hz - 1 80 kHz
Crest factors up to 5
Manual or remote control of filter scanning
AC or DC outputs to Recorders
50 dB logarithmic DC output
Manual control of avo
time fur 2607 , 2120 , m2010
proportional to RMS Level
A , B, C,
D-weighting networks
Digital bus control of filter
Range settings shown on meter
scanning and averaging times
scale
for 2607 and 2120
This combination gives optimum
use of all meas urem e nt and
control facilities , including
X-V recordin!'l (not 2010)
Table 1. Band Pass Filter and Measuring Amplifier Combinations