32
Fig.
4.2.
The
Portable Level Recorder Type 2306
With AC recording, on the other hand, the AC output signal
of
the 2512 is rectified and
averaged by the rectifier and writing system
of
the recorder. This extracts the RMS level
of
the
measured vibration signal level, and plots it with a logarithmic amplitude (linear dB). However,
the lowest lower limiting frequency available on the level recorder lies within the frequency
range
of
WHOLE BODY measurement and therefore can affect measurements.
In
addition, the
time constant is no longer determined by the Type 2512 but by the level recorder writing
system, and will not in general fulfil the relevant recommendations. It is therefore recommend-
ed that level recordings are made from the DC OUTPUT
of
the 2512 whenever possible, using
the
"DC
Lin." RECORDING MODE
of
the level recorder.
A reference signal
for
setting up and calibrating the level recorder can be obtained from the
Type 2512, i.e. its internal reference signal,
or
directly from the Accelerometer Calibrator Type
4291.
In
practice, however it will generally be found more convenient to use the internal
reference signal of the 2512. This is -because internal compensation is made
for
the effect
of
the frequency weighting filters
on
the
16
Hz
reference signal so that the reference signal
delivered
to
both the meters and
to
the DC OUTPUT socket always corresponds to 1
ms-
2
(120 dB) in the WHOLE BODY mode and to
10
ms-
2
(140 dB) in the HAND-ARM mode, i.e.
20
dB above the lower measurement limit.
The signal from
an
accelerometer vibrated by the Accelerometer Calibrator will be weighted
differently by each
of
the weighting filters in the 2512 giving a different calibration value
for
each mode. Furthermore, the frequency at which the Accelerometer Calibrator operates lies at
one end
of
the WHOLE BODY frequency range.
It is therefore recommended that the internal reference signal
of
the 2512 is used
for
level
recorder calibration purposes whereever possible.
The setting up and calibration procedure
for
recording from the 2512 is similar for both the
Type 2306 and the Type 2309, so in the following procedures specific reference is made only
to
the Type 2306.
To Next Page
Loading...
