Casella CEL CEL-160 - Manual (Page 12)

Full scale deflection sensitivity for the CEL-160
may be set within the range 2.0 to 7.0 V. As
these types of transducer provide signals that
are linear in mV the amplitude scale
annotations will not be correct, and the most
convenient configuration would be to use the
50 dB dynamic range switch and use the D key
to produce a 0 - 50 scale which is then read off
in percent FSD with a scale multiplier of 2.
Remember if the 20 dB or 10 dB dynamic
ranges are selected, only the top portion of the
dynamic span will appear on the readout, with
the remainder dropping off scale.
4.3 AC Inputs
The signal source should be connected via a
screened cable to the direct AC input pin of
the preamplifier connector. See Fig. 1. This has
an input impedance of 220 kΩ and will accept
signals up to 80 V pk-pk . All three gain controls
are in circuit but it must be remembered that
they are arranged to take account of the gain
switching in the preamplifier. The relative gain
provided by the RANGE (dB) switch is,
therefore, as set out in Fig 4.
The nominal sensitivity for auxiliary AC
inputs is 5 V RMS for full scale on the 120 dB
RMS range with the GAIN-CAL control in the
CAL position and the SLM gain control mid
range. Sensitivity in AC mode is -10 dB to
ensure signals within the instrument's crest
factor remain on scale.
Having connected the input signal the
amplifier gain may be trimmed using the
GAIN-CAL and SLM calibration controls. The
CEL-177 Precision Acoustic Calibrator may be
used to calibrate the system by using the
100 mV reference voltage.
It is preferable to use the 'SLM Gain'
control to calibrate the auxiliary AC input as it is
then possible to preserve any previous DC
calibration. Having completed the calibration
the RANGE (dB) control is used to change the
measurement range bearing in mind the
relative gains shown in the table (Fig 4).
Having set the measurement range,
scale annotations should be set using the D
key. Annotations will be preserved between
the 90 dB and 120 dB ranges but will need to
be reset if the measurement sequence moves
into the 40 - 80 dB or 130 -140 dB ranges.
5. Modes of Operation
5.1 Recording Sound Pressure
This represents one of the prime applications
for the CEL-160 and hence it is equipped with
all the necessary features found in a full
specification sound level meter. When fitted
with a CEL-2980 preamplifier and
measurement microphone the instrument
conforms to the International Standard IEC 651
Type 1 (precision) specification.
The recommended measurement
microphone is the CEL-186/2F. This is a
0.5 inch high stability measurement
microphone having a free field response. For
those applications requiring a random pressure
characteristic the CEL-186/2PR should be
specified. These microphones will enable
measurements to be made over the range 23 -
140 dB(A) and it is recommended that they are
used in conjunction with a CEL-2962
windshield. The lower measurement limit may
be improved by specifying the CEL-190
microphone which will give coverage of 13 -
130 dB(A). The microphone-preamplifier
assembly should be mounted in the
measurement location on a CT3 tripod. For
measurement in exposed locations or for
permanent outdoor installations the CEL-194
Outdoor Microphone System and CEL-176/3
Control Amplifier are required. Full details are
available on request.
Calibration is performed by means of
the CEL-177 Precision Acoustic Calibrator full
details on which are published separately.
5.2 Recording Vibration
The addition of the CEL-3025 vibration
attachment to the CEL-2980 preamplifier
Range (dB)
Switch Setting
40 50 60 70 80 90 100 110 120 130 140
Relative Gain (dB) +50 +40 +30 +20 +10 +30 +20 +10 0 +10 0
Figure 3: Time annotation at various paper speeds
Page 12 - CEL-160 Graphic Recorder