
Digital modules
4.6 Input characteristic curve for digital inputs
S7-400 Automation System Module Data
Reference Manual, Edition 09/2009, A5E00850736-06
105
4.6 Input characteristic curve for digital inputs
IEC 61131, type 1 and type 2
The IEC 61131 standard requires the following for the input current:
● In the case of type 2, an input current of ≥ 2 mA already at + 5 V
● In the case of type 1, an input current of ≥ 0.5 mA already at + 5 V
EN 60947-5-2, 2-wire BEROs
The standard for BEROs (EN 60947-5-2) specifies that there can be a current of ≤ 1.5 mA
for BEROs in the "0" signal state.
The input current of the module in the "0" signal state is decisive for the operation of 2-wire
BEROs. This must be in accordance with BERO requirements.
Input characteristic curve for digital inputs
As long as the current flowing into the module remains ≤ 1.5 mA, the module recognizes this
as a "0" signal.
0,5
1,5
2
6
7
0 5 11 13 15 24 30 L+ (V)
- 30 V
I
E
(mA)
“0” “1”
1
0
L+
M
I < 1,5 mA
Typ. switching threshold(9.5 V)
Resistance characteristic curve
I
min
to IEC 61131; type 2
BERO
standard
I < 1,5 mA
PLC input resistance
--> “0” Signal
2-wire BERO
I
min
to IEC 61131; type 1
Figure 4-1 Input characteristic curve for digital inputs
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