Attenuation Characteristics and Step Response Characteristics
(a) Attenuation characteristics
You can use the moving average filter to significantly attenuate the signals in the specific fre-
quency and the frequencies that are integer multiples of that frequency.
The following calculation formula shows the relationship between the frequency f
N
and the set
value of the moving average count.
Set value of moving average count =
(1 ÷ Digital Filter Processing Period [µs]) × 1,000,000 [Hz]
ƒ
N
[Hz]
For example, to improve the attenuation effect by 1 kHz when the Digital Filter Processing Pe-
riod is 5 µs, the set value of the moving average count can be calculated as follows:
Set value of moving average count = ((1 ÷ 5 µs) × 1,000,000) ÷ 1,000 Hz = 200 times
Digital Filter Processing Period
on page 8 - 19 for information on the Digital Filter
Processing Period.
Set the moving average count based on the above formula.
The figure below shows an example of attenuation characteristics in the following case: only
the moving average filter 1 is used, the moving average count is set to 200 times, and the Digi-
tal Filter Processing Period is 5 μs.
As shown in the attenuation characteristics below, you can significantly attenuate the signals in
the frequencies of 1 kHz and the frequencies that are integer multiples of 1 kHz. Note that the
attenuation characteristics shown in these graphs are based on theoretical values.
0
−
10
−
20
−
30
−
40
−
50
−
60
−
70
−
80
−
90
0
1 k
2 k
3 k
4 k
5 k
6 k
G
a
in
[
d
B]
Frequency [Hz]
(b) Step response characteristics
The figure below shows step response characteristics in the following case: only the moving
average filter 1 is used, the moving average count is set to 200 times, and the Digital Filter
8 Functions
8 - 26
NX-series Analog I/O Units User’s Manual for High-speed Analog Input Units (W592)
