Casella CEL CEL-160 - Manual (Page 13)

converts the instrument into a comprehensive
vibration waveform and level recorder. The
results provided are available in terms of either
vibration acceleration, velocity or displace-
ment. The instrument is calibrated to the
accelerometer via the 100 mV reference
voltage provided by the CEL-177 Precision
Calibrator or alternatively the accelerometer
may be mounted on the RS11032 Transducer
Calibration Table.
In addition to the full range of general
purpose measurements the CEL-160 will
prove particularly valuable in providing hard
copy results of vibration signals for use in
machinery preventative maintenance program-
mes; program Level 2 versions are particularly
well suited to shock measurements. An option
schedule provides for an additional +18 V DC
bias to be provided to the preamplifier socket
that will allow direct connection of
accelerometers having integral preamplifiers.
Full details are given in Section 12.
5.3 RMS Level Recording
Recording of signal RMS level may be made
across the full range of paper speeds with any
of the four time constants and in linear or
logarithmic units. In the case of logarithmic
traces the dynamic range may be set as either
10 dB, 20 dB or 50 dB. In order to provide a
continuous trace between the individual points
plotted by the recorder the controlling program
allows for each individual point to be joined by
a continuous line. This means that to go from
minimum to full scale deflection each of the
100 discharge pins will be fired in turn. As it
takes 50 µS to fire each pin, the minimum time
to cross the paper is 5 mS.
Considering that most traditional
electro-mechanical level recorders are limited
to 150 mS to cross their charts it can be seen
that the CEL-160 is some 30 times faster. This
will ensure that the levels are faithfully
recorded without distortion by the writing
system. Further improvements are available by
operating the CEL-160 in the AC or Transient
Capture modes.
For details of level against frequency
recording refer to Section 6 of this manual.
5.4 Waveform Recording
Selecting the AC mode of operation enables
the CEL-160 to operate as a recording
oscillograph. To obtain this function the
digitised AC signal is applied direct to the
writing head control circuits with the centre
line of the trace representing 0 V. Each pin is
fired as it receives a sample and the link line is
not therefore provided. There is therefore no
limiting factor to the writing speed. The pin
discharge rate is 27,750 per second. At the
fastest paper speed the highest individual
frequency that can be resolved is in the order
of 20 Hz but the envelope of frequencies up to
10 kHz can be clearly resolved.
The transient capture facility in the level
2 version will enable detailed examination of
frequencies up to 10 kHz. It should be noted
that in this mode of operation the rate of pin
discharge is very high and in addition high
paper speeds are usually used. These two
factors cause a high power consumption and
can quickly discharge the batteries, and it is
recommended that the CEL-3731 NiCad
Battery pack is used in these measurement
configurations.
In order to ensure that AC signals
remain on scale the sensitivity in this mode is
reduced by 10 dB relative to the RMS modes.
This amount corresponds to the crest factor of
the RMS detector, hence any AC signal that
remains on scale will be correctly processed
by the RMS circuits.
5.5 Recording DC Levels
The CEL-160 may be used as a general
purpose level recorder by applying the input to
the DC input connector and selecting the DC
mode. A recording span from 0 V to levels
between 2 and 7 V FSD will be obtained on
the 50 dB dynamic range setting with any
offset requirements being arranged externally.
The 20 dB and 10 dB dynamic range setting
will provide for the appropriate top part of the
scale to be expanded in order to improve
resolution. Forfurtherdetails refer to section 4.2
6. Operation with
Frequency Analysers
The CEL-160 may be used to produce
recordings of level against frequency by
connecting it to a suitable frequency analyser.
It is primarily intended for operation with the
CEL-196 Automatic Third Octave Filter Set but
may also be coupled to a wide range of other
serial or real time analysers. The various filters
programmed as standard are listed under the
CEL-160 Graphic Recorder - Page 13