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8.1
FILTER PARAMETERS
The digital filters of the 3411 are used to remove undesired noise from the TSC inputs. This noise
could be conducted from electrical sources or mechanical vibrations.
The input of the A/D converter internal to the 3411 has a traditional analog filter that is comprised
of the following characteristics:
•
-3db Point: 3.8 kHz
•
A/D Sample Rate: 7812.5 Hz
•
16 acquired and averaged samples: average applied to filter at a rate of 488.28125 Hz
•
Filter Cutoff Frequencies: 2 Hz, 5 Hz, 10 Hz, 20 Hz, 50 Hz, 100 Hz
•
Filter Output: Equivalent to second order Butterworth analog filter
•
Transposed Direct Form II Architecture: The diagram below shows this architecture.
x(n)
With a digital filter, the 3411 is able to solve the following equations:
y(n)
w1 =
w2 =
The equations are applicable to each channel, occurring every 2.48 milliseconds.
8. Theory
b
0
b
1
b
2
Transposed Direct Form II
Figure 8–1 Transposed Direct Form II Architecture
=
b
* x(n) + w1
0
b
* x(n) - a
* y(n) + w2
1
1
b
* x(n) - a
* y(n)
2
2
+
-1
Z
w1
+
-1
Z
w2
+
39
y(n)
-a
1
-a
2
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