Casella CEL CEL-160 - Manual (Page 16)

There are five selectable sample rates
giving a trade off in transient duration and
upper limiting frequency. These are selected
by a number code followed by keying the letter
A, the full details are given in Fig 7. For the full
1800 word store to be replayed will result in
approximately 2 m of paper being consumed.
Many applications are concerned with
events that are considerably shorter than the
maximum provided and in these cases it is
possible to limit the amount of data replayed
and this is achieved by entering the second
number code followed by A after the sample
rate code, full details are given in Fig 8. When
block length 9 is selected the paper will
continue to feed until the signal has dropped
below ±15% deflection.
Sample Rate Key 0 1 2 3 4 A
Sample Rate (µS) 36 108 360 1080 3600 +
Upper Frequency
Limit (Hz) 10 k 3.3 k 1 k 330 100
Max Capture
Duration (mS) 66 194 660 2000 6600
Time Grid (mS) 1 3 10 30 100
Equivalent Paper
Speed (m/S) 29 10 3 1 0.3
Figure 7: Parameters of transient
capture system
The arrangement of the data capture circuits is
such that when the EXP. TRACE-OFFOPTION
switch is in the expanded position and the
recorder is set for AC waveform recording the
paper is stationary. The sample of the
waveform is taken when the signal amplitude
exceeds ± 30% deflection and as soon as it is
completed the waveform is printed at the
30 mm/S speed and the data store reset. The
printout is headed by the real time and the
time grid spacing. The trace takes the form of
128 samples of pre-trigger information
followed by the selected block length. At the
end of the printout the recorder again stops to
await the next trigger.
It is important to understand the method
of transient capture and recording in order to
interpret the results. The recording is produced
by sampling the level of the input signal at
intervals corresponding to the sample rate.
These points are then reproduced on the paper
and joined together with a straight line. When
recording signals which have much lower
frequencies than the sample rate this effect is
not noticeable and a true result appears.
However, at frequencies approaching one fifth
or more of the sample rate the straight lines
Block Length Key 5A 6A 7A 8A 9A
Store Size
(words) 1800 1000 500 128 T'hold
Capture Duration
in mS
35 µS rate
108 µS rate
360 µS rate
1080 µS rate
3600 µS rate
66
194
660
1940
6600 36
100
360
1000
3600 18
50
180
500
1800 5
14
50
140
500 -
-
-
-
-
Figure 8: Selectable store size for
transient capture
Figure 9: Output format in transient capture mode
Page 16 - CEL-160 Graphic Recorder