4.2.1. DC Linear Recording
DC Linear recording is easy
to
calibrate and perform, and, because
of
the low frequencies
encountered in human vibration measurements and the reasons given in the above section, is
recommended for use with the 2512 whenever possible. The dynamic range
of
the 2512 is
46
dB, which fits conveniently with the
50
dB potentiometer available
for
the 2306. The
procedure is as follows:
1.
Fit the Level Recorder with the
50
dB potentiometer and a roll
of
suitable recording paper
(QP 0102 is recommended
for
general purposes), and switch the level recorder on by
pressing in the POWER push-button.
2.
Set the RECORDING MODE switch on the level recorder
to
the
"DC
Lin"
position and turn
the SENSITIVITY switch to
"O".
3.
Make sure that there is no connection to the SIGNAL INPUT socket
of
the level recorder,
switch the
PEN
DRIVE on by pressing the push-button in, and adjust the DC LIN.
POSITION control
to
line the pen up with one
of
the thick lines, e.g. the thick line at the
bottom
of
the recording paper. Then set the POLARITY switch on the side
of
the level
recorder to
"+
".
4.
Connect the DC OUTPUT socket on the 2512 to the SIGNAL INPUT socket on the level
recorder using the BNC
to
BNC cable AO 0087.
5.
Using the internal reference source
of
the 2512, i.e. with the CHANNEL SELECTOR
of
the
2512
in
the
"Ref"
position and any
of
the HAND-ARM
or
WHOLE BODY 1 -
80
Hz
pushkeys activated, adjust the SENSITIVITY control on the Level Recorder so that the pen
lies
20
d B above the line chosen in step
3,
i.e. on the third thick line from the bottom
of
the
paper as shown in the example
of
Fig.
4.3.
OODOODOODODOOOOODODOOODODDOOOOODODDDDDODDDDOODODDD
Briiel &
Kjaer
Bru·
1
~~
Kjaer
dB
170_
Internal reference Level
from
2512
=160
(10
ms
-
2)
=160
(100
ms
-
2
)
120 dB
(1
ms
2)
for
Whole Body
150 _
140 dB (10
ms
2)
for
Hand-
Arm
130
120
(1
ms
2)
160 (10
ms
2)::
lower
Limit
of
measurement
100 dB (0, 1
ms
2)
for
whole Body
110
130--------==
120 dB (1,0
ms
2)
for
Hand-
Arm
100
(0
, 1
ms
2)
120
(1
ms
21=
OP
0102
WB H - A
810428
Fig.
4.3.
Calibrating the Level Recorder
As the internal reference voltage
of
the 2512 corresponds to a vibration level
of
1
ms-
2
(120 dB re
10--s
ms-
2
)
in
the WHOLE BODY mode
or
10
ms-
2
(140 dB re
10--s
ms-
2
)
in the
HAND-ARM mode, these lines should be labelled accordingly. The bottom line corre-
sponds
to
0,
1
ms-
2
and the top line corresponds to
30
ms-
2
(100 to
150
dB) in the WHOLE
BODY mode and to 1
ms-
2
to 300
ms-
2
(120
to
170
dB) in the HAND-ARM mode.
The pen deflection will now correspond to the RMS value
of
the vibration level measured
continuously by the Type 2512, with the averaging time corresponding to the mode
selected. It is this value which is displayed on the analogue meter. The digital meter
displays only the equivalent continuous
or
peak levels.
6.
Select a suitable PAPER SPEED setting and set the WRITING SPEED/LF LIMIT control to
"250
mm/s
/
25
Hz".
33
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