836
FX
3U
/FX
3UC
Series Programmable Controllers
Programming Manual - Basic & Applied Instruction Edition
36 Operation of Special Devices (M8000 -, D8000 -)
36.2 Supplement of Special Devices (M8000 - and D8000 -)
36.2.9
Input filter adjustment [D8020]
The inputs X000 to X017
*1
have a digital filter circuit with a setting range of 0 to 60 ms. The digital filter setting
value is set between 0 to 60 ms (in 1 ms steps) in special data register D8020. After PLC powers ON, D8020
is automatically set to K10 (10 ms).
*1.
X000 to X007 in the FX
3U
-16M
1. Program example for adjusting the input filter
When the program shown below is executed, the filter constant is changed to 0 ms.
Because the C-R filter is provided in the hardware, however, the filter constant is actually a value shown in
the table below when "0" is specified.
*1.
When setting the input filter to "5
µ
s" or when receiving pulses whose response frequency is 50 k to
100 kHz using high speed counters, perform the following:
-
Input wiring length should be 5 m (16' 4") or less.
-
Connect a bleeder resistor (1.5 k
Ω
, 1/2 W) to an input terminal. The load current of the open
collector transistor output in the device on the other end should be 20 mA or more including the
input current of the PLC.
*2.
X000 to X007 in the FX
3U
-16M
• The input filter constant can be changed as many times as need in the user program.
• This input filter adjustment described here is not required when using high speed counter, input interrupt,
or pulse catch (M8170 to M8175) functions.
Input number
Input filter value when "0" is set
X000 to X005
5
µ
s
*1
X006, X007
50
µ
s
X010 to X017
*2
200
µ
s
X000
Input
terminal
0ms
1ms
10ms
60ms
0
1
10
60
Image
memory
X017
*1
Input refresh
Determined by the contents of D8020 (initial value: 10)
Filter
M8000
RUN monitor
FNC 12
MOV
K 0
D8020
