The major requirement for deterministic signals is that the ripple be reduced to an ac-
ceptable level. Where only a single sinusoidal component is included in the bandwidth
the ripple will be reduced to less than ± 1/4 dB for:
.....
BOO
530
500
400
250.
160
10
0
63
40
25
168
le
.4
1
#
#
2
W
_wry
/ ."
I
11[111
I
l
111111 I I
111111
I 1 111111
3
T —
A f
where f is the frequency of the single component.
(5.13)
If the bandwidth contains several sinusoidal components, which is possible with third-oc-
tave analysis, Equation (5.13) still applies when f is interpreted as the minimum separa-
tion of any two of the components (lowest beat frequency). When a large number of com-
ponents are contained within the bandwidth, as at higher frequencies the signal should
be treated as random.
5.3.2. DC or AC Recording
Generally, it is preferable to use DC recording when possible, but where no DC output is
available from the Measuring Amplifier, or where it has a dynamic range less than
required, AC recording must be employed. Using AC recording it is possible to achieve a
75dB dynamic range with an appropriate potentiometer in the Level Recorder (not Type
2306). Where a choice between DC and AC recording has to be made, the paper speed
obtained for either possibility should be investigated, as AC recording can be just as fast,
and may be preferable, to give averaging times less than 0,1 second for example.
5.3.3. Writing Speed
WRITING
SPEED
mm/sec
50 mm
Writing
Width
0.001 0.01 0.1
Effective Averaging Time (seconds)
Fig.5.2. Effective averaging times as a function of the Level Recorder writing speed
2000
1600
1250
1000
800
500
315
200
125
80
50
31.5
16
4
1.0
10.0
113109
WRITING
SPEED
mm/sec
100 mm
Writing
Width
27
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