Rockwell Automation 1794-OB16D FLEX I/O Diagnostic Modules User Manual - Manual (Page 31)

Publication 1794-UM061A-EN-P - July 2006
About the FLEX I/O Diagnostic Output Module 29
You must connect dummy resistors to unused sensor power ports to mask the
diagnostic function. If these external resistors are not used, the module’s
sensing circuitry will not detect the intended voltage or current and signal a
module fault. The channel fault indicator and the module’s fault indicator will
light, and the module’s open and error bits are set, thus rendering fault
detection of the remaining channels useless. The recommended value of this
dummy resistor is 10 K
Ω (+10%), 1/8 W (or larger). The resistor is wired
between unused output channels and common. The figure depicts wiring of a
dummy resistor.
Diagnostic Fault Detection
The module monitors current and voltage at each output channel terminal,
and monitors the user supply for reverse supply voltage. The figure below
shows the location of these fault monitors within the 1794-OB16D diagnostic
output module.
User Power
Open Wire
Detect
Current
Shorted
Output
Monitor
Fault Indicator
-
Reverse
Short
Open
Output
V+
Open Wire
Monitor
Reverse
Voltage
Monitor
Output Indicator
Output
Fl
exb
us
In
te
rf
ac
e
+
40117C
Current Limiting
Thermal Prot.
Output FET