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MELSEC-Q 
2   INPUT MODULE SPECIFICATIONS 
2.21 QX81 DC Input Module (Negative Common Type) 
Type 
Specifications 
DC input module (Negative common type) 
QX81 Appearance 
Number of input points  32 points 
 
Isolation method  Photocoupler 
Rated input voltage  24VDC (+20/-15%, ripple ratio within 5%) 
Rated input current  Approx. 4mA 
Input derating  Refer to the derating chart. 
ON voltage/ON current  19V or higher/3mA or higher 
OFF voltage/OFF current  11V or lower/1.7mA or lower 
Input impedance  Approx. 5.6kΩ 
Response 
time 
OFF to ON 
1ms/5ms/10ms/20ms/70ms or less (configured in PLC parameter)  1  
(Default: 10ms) 
ON to OFF 
1ms/5ms/10ms/20ms/70ms or less (configured in PLC parameter)  1  
(Default: 10ms) 
Dielectric withstand voltage  560VAC rms/3 cycles (altitude 2000m) 
Insulation resistance  10MΩ or more by insulation resistance tester 
Noise immunity 
By noise simulator of 500Vp-p noise voltage, 1 s noise width  
and 25 to 60Hz noise frequency 
First transient noise IEC61000-4-4: 1kV 
Protection degree  IP2X 
Common terminal arrangement  32 points/common (common terminal: 17, 18, 36) 
Number of occupied I/O points  32 points (I/O assignment is set as a 32-point input module.) 
Operation indicator  ON indication (LED) 
External connections  37-pin D-sub connector 
Applicable wire size 
0.088 to 0.3mm
2 
(For A6CON1E) 2 
Applicable connector  A6CON1E, A6CON2E, A6CON3E (optional)  
Applicable connector/terminal block 
converter module 
A6TBX36-E, A6TBX54-E, A6TBX70-E 
Internal current consumption 
(5VDC) 
75mA (TYP. all points ON) 
(0.08A is shown on the rating plate of the module.) 
Weight 0.16kg 
 
Derating chart  Pin-Outs 
Pin 
No. 
Signal 
No. 
Pin 
No. 
Signal 
No. 
 
 
Module front view 
1 X00 9 X10 
20 X01 28 X11 
2 X02 10 X12 
21 X03 29 X13 
3 X04 11 X14 
22 X05 30 X15 
4 X06 12 X16 
23 X07 31 X17 
5 X08 13 X18 
External connection 
24 X09 32 X19 
 
6 X0A 14 X1A 
25 X0B 33 X1B 
7 X0C 15 X1C 
26 X0D 34 X1D 
8 X0E 16 X1E 
27 X0F 35 X1F 
17 COM 37 Vacant 
36 COM 19 Vacant 
18 COM     
 
1
: For the setting method, refer to Section 1.3.1. 
2: When using A6CON2E or A6CON3E, refer to Chapter 7.
 
 
QX81
24VDC
4mA
QX81
01234567
8 9ABCDEF
01234567
8 9ABCDEF
100
90
80
70
60
50
40
0102030405055
ON
ratio
28.8VDC
(%)
(     )
C
Ambient tem
erature
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1