Rockwell Automation 1715-OF8I Redundant I/O System User Manual - Manual (Page 277)

Rockwell Automation Publication 1715-UM001C-EN-P - March 2014 277
1715-IB16D Digital Input Module Diagnostics Appendix C
Calculate the Voltage for Off/On Conditions for Threshold Values
The following examples calculate the voltage for an ‘off ’ condition with the
switch opened and closed.
Open Switch/Off Condition
With SW1 open, current flows through R1 and R2 (15 + 3.9 k  18.9 k  . We
can calculate the voltage that is present at the input of the input module and by
using a voltage divider circuit, we can calculate the voltage for an ‘off ’ condition.
Figure 75 - Open Switch/Off Condition
Shield
(if used)
Terminal
Blocks
OV
20 Ω
100 Ω
50 mA
4.99k Ω
Termination
Assembly
+24V dc
R1
R2
45678
User-calculated Voltage
5.1K SW1
3.9k
15k
45680