100
90
80
70
60
50
40
30
20
10
0
500
0
1000
1500
Amp
lit
u
d
e
[
%
]
Time [µs]
Step response
time
Step signal
fc = 1 kHz
The step response times for typical cutoff frequencies are shown below.
Cutoff frequency [Hz] Step response time [µs]
10
36,646.8
100
3,664.7
1 k
366.4
10 k
36.2
50 k
4.5
The smaller the cutoff frequency is, the wider range of noise you can remove. This stabilizes the
analog input values, but causes the step response time to increase. When you use the digital low-
pass filter, the analog input values are measured with a delay in response to the input as shown in
the step response characteristics. When the NX bus I/O refreshing is executed in the middle of digi-
tal low-pass filtering, the analog input values in the middle of digital low-pass filtering are sent to
the CPU Unit or communications master. Set the cutoff frequency that is most suitable for the
measurement.
Moving Average Filter
This function calculates the average of the input signals for the set moving average count and uses it
as the analog input value.
You can use the moving average filter to significantly attenuate the signals in the specific frequency
and the frequencies that are integer multiples of that frequency.
To attenuate two frequencies, combine the moving average filter 1 and moving average filter 2.
Description of Operation
The moving average processing of the Unit is shown below using the moving average count of 4 as
an example.
8 Functions
8 - 23
NX-series Analog I/O Units User’s Manual for High-speed Analog Input Units (W592)
8-5 Digital Filtering
8
8-5-2
Details on the Function
