BRUEL & KJAER 2512 - Page 9

Seat
Accelerometer
Input
z
Input
1
Input
2
Power Supply
External Supply 6 to 15 V DC Indicator
Charge 12 V DC
Internal
Reference Battery &
Oscillator
Power
Supply
Frequency-
Input
Low-Pass
Amplifier Filters
Input
Amplifier
28 V, 2 mA
DC Output
AC
Output
Weighting Filters
Whole-Body
X and Y axes
Whole-Body
Z axis
Hand-
Arm
Mot. Sickness
Red . Comfort
Mot . Sickness
DC Output
Analogue
Meter
IEC
Interface
(Addres-
sable)
IEC
Interface
Bus
Digital
Display
System Control Logic
and Timer, controls the
function of most blocks
i~H .V. Category
Input
Amplifier
Sev. Discomf.
Log Peak :=====-=-=-=--=--=--=--::...-::...
Detector
- H.V. Criterion I
- Display Mode
-Measurement
Start-Stop-A eset
Switch
Setti ngs
on
Front
Pane l
Input
3
791072/ 1
Fig.2. Simplified schematic block diagram of the Human-Response Vibration Meter Type 2512
Description
The various facilities included in
the 251 2 are described in the fol-
lowing sub-sections. Fig.2 is a sim-
plified schematic block diagram
showing the 2512's "black box" lay-
out.
Signal Input and Transducers
Any one of the three input sock-
ets
on the front panel can be se-
lected by
means of the adjacent
slide switch to provide a signal for
measurement. The 6-pin DIN input
socket on the rear panel, which ac-
cepts
the connecting cable for the
Triaxial Seat-Accelerometer Type
4322 , is wired in parallel with the
three sockets on the front panel.
The
X, Y and Z positions on the se-
lector switch cbrrespond with the
three individual measuring direc-
tions of the seat transducer .
The
sens i tivity of the 251 2 is cali-
brated to suit transducers having a
sensitivity of 1 pC/ ms -
2
. Several
B
& K Uni - Gain® transducers are su-
itable . Traixial Seat- Accelerometer
Type 4322 is mainly used for whole -
body
and motion sickness measure-
ments with seated persons, but can
also be
strapped to the chest . Triax -
ial
Accelerometer Type 4321 and
single -axis Accelerometer Types
4371 and 4384 can be mounted
on the handle of tools for general
hand-arm measurements . Miniature
Accelerometers Types 4374 'and
4375 are especially suitable where
a hand - arm measurement handle is
employed . With pneumatic tools ,
which yield very high acceleration
peaks, the High g Accelerometer
Type 8309 should be used; alterna-
tively other accelerometers can be
used
together with the mechanical
filter UA 0559 .
For
very low level and low fre-
quency vibrations, such as in mo-
tion sickness and building vibration
measurements , the single-axis Ac-
celerometer Type 4370 or the very
high sensitivity Accelerometer Type
8306 are recommended .
An appropriate correction factor
must be applied to peak and Leq
readings when using accelerome -
ters having a sensitivity other than
1 pC / ms-
2
. Exposure dose read-
ings are ignored in this case but the
exposure dose can be evaluated us-
ing Fig .7 .
The mi
nimum measurable levels
with the 251 2 are as follows. With
8306
Fig.3. Some accelerometers suitable for use
with the 2512
Accelerometer Types 4321, 4322 ,
4371 and 4384, 0, 1 ms-2; With
Type 4370, 0 ,01 ms- 2 ; and with
Type 8306, 0,001 ms-2 . Acceler-
ometer Type 8306 has a built-in
preamplifier requiring a 28 V, 2 mA
power supply, this is provided from
a socket on the front panel of the
2512 .
Vibration signals recorded on Por-
table Tape Recorder Type 7003
may be input to the 251 2 via a spe-
cial adaptor.
Frequency-Weighting Filters
The frequency weighting filters in-
corporated into the 251 2 are in
agreement with the relevant stand-
ards and recommendations for the
three categories of human vibration
which it measures . Fig.4 shows the
filter characteristics graphically . The
reference levels, 0 dB, for the
curves in Fig .4 are a function of
several factors as specified by the
relevant standards and recommen-
dations . These factors are tabulated
in Fig .5.
Sockets are provided on
the rear
panel (Fig .1) for connecting an exter -
nal
filter which can be used to-
gether with, or instead of, the built-
in weighting filters. The 8 & K Third-
Octave and Octave Filter Set Type
1 61 8
(mains powered) and Tunable
Filter Type 1 621 can thus be cou-
pled directly to the 251 2. Measure-
ments with external filters are of
3