Rockwell Automation 1791-XXXX Discrete I/O AC and DC Block I/O Input and Output Modules - Manual (Page 14)

I/O Interface and System Design
Chapter 2
2-4
Example: You want to use an ac 2–wire Bulletin 871C Proximity Switch
for an input to a block I/O module. To determine if the switch is
compatible with the block, verify the following:
I
block-off
> I
leakage-switch
V
supply
- V
switch-on
> V
block-on
where:
I
blockĆoff
= minimum off-state current of block input
I
leakageĆswitch
= maximum off-state leakage current of proximity switch
V
supply
= minimum value of supply voltage
V
switchĆon
= maximum on-state voltage drop of proximity switch
V
blockĆon
= minimum on-state voltage specification
Simplified schematics of ac and dc input circuits are shown in Figure 2.3
and Figure 2.4.
Figure 2.3
Simplified Schematic of ac Input Circuit
Opto
Isolation
Input
Filter
Input
Indication
LED
(logic)
System
Circuitry
3.16K Ω
27K Ω
27K Ω
33 Ω
33V
0.2 µ F
79-132V ac
Input
Common
L1
L2
Figure 2.4
Simplified Schematic of Sinking dc Input Circuit
Opto
Isolation
Input
Filter
Input
Indication
LED
(logic)
System
Circuitry
+10-30V dc
+
464 Ω
2.8K Ω
DAN212K
Return
Common
-
Input
18555