Casella CEL CEL-160 - Manual (Page 19)

9.1 PSS, Preset Start & Stop Bands
This facility is utilized by the CEL-160/2B RT60
Measurement option which allows the
operator to select appropriate measurement
start and stop frequency bands through the
keyboard. It is only applicable to CEL filter sets
(See CEL-160/2B Operating Instructions for full
details).
9.2 VSD, Variable Settling Delay
In order to ensure the highest accuracy
achievable during automatic frequency analysis
the frequency switching software introduces a
delay between switching bands. The delay is
variable and depends upon the filter set in use,
the paper speed selected at the start of the
sweep, and the bandwidth to be analysed.
The minimum delay time of 250 mS
applies to a paper speed of 3 mm/S, and is
increased according to the table in Figure 12,
as are any longer delays, when other paper
speeds are selected.
Longer delays than the minimum delay are
required at low frequency and when switching
from an "All-Pass" band to the first analysis
band. Each filter set control program contains a
default start delay which for the CEL-296 third
octave mode is 640 mS and for the CEL-288
low frequency modes is 12.5 S. This time is
doubled for the transition from "All-Pass" to the
first analysis band, and it then subsequently
reduces each 1/3 octave such that it halves for
each octave analyzed until the minimum delay
time is reached.
It should be noted that the switching
delay is not related directly to frequency band
dwell times which are controlled by the initial
paper speed set when commencing the
frequency scan. As the frequency increases
the filter dwell-time can be decreased and the
software incorporates reduced filter dwell
times by increasing the paper speed by a 10:1
ratio to a maximum paper speed of 10 mm/S
during a frequency scan (except CEL-288
scans which have a maximum paper speed of
3 mm/S).
Thus for a CEL-296 filter set operated in
third octave mode with an initial paper speed
of 4B - 1 mm/S, the delay between "All-Pass"
and 6.3 Hz will be 2.56 seconds and will have
been subject to the minimum delay at all
bands from 50 Hz upwards.
10. Options and
Modifications Schedule
10.1 Additional Power Supply for
Preamplifier
A hardware option provides an
additional +18 V DC supply (5 mA) to
the spare pin on the pre-amplifier
connector. This supply will enable the
direct connection of accelerometers
having integral preamplifiers as well as
allowing use with the CEL-165/2
preamplifier and CEL-194X outdoor
microphone system.
The power supply is contained on
a printed circuit panel that is mounted
on the main printed panel within the
recorder. It may be specified with new
CEL-160 Address Filter Set Frequency Range
11F B & K 1618 AP, A, 2 Hz to 16 kHz 1/3 oct AFR 43 bands
12F B & K 1621 20 Hz - 20 kHz Narrow Bard Semi AFR
13F B & K 1621 2 Hz - 2 kHz Narrow Bard Semi AFR
14F - 19F Default to 6F
Note: AP = All Pass,(Linear) band.
VSD = Variable settling delay controlled by CEL-160.
AFR = Automatic Frequency band changing.
PSS = Preset start & finish bands possible.
Figure 11 (continued): Validity of analyser systems with software version 09
CEL-160 Paper Speed Delay Multiple eg Minimum Delay
1 - 3B 3.0+ mm/S 1 x default delays 120 mS
4B 1.0 mm/S 2 x default delays 500 mS
5B 0.3 mm/S 4 x default delays 1 S
6B 0.1 mm/S 6 x default delays 1.5 S
7B 0.03 mm/S 8 x default delays 2 S
8B 0.01 mm/S 10 x default
delays 2.5 S
Figure 12: Delay times
CEL-160 Graphic Recorder - Page 19