Rockwell Automation 1794-OB16D FLEX I/O Diagnostic Modules User Manual - Manual (Page 107)

Publication 1794-UM061A-EN-P - July 2006
Interpret the Indicators
105
For 3-wire sensors:
• an open fault will be detected when an open occurs on either the
sensor-power wire, the sensor (-V) wire, or the high-current portion of
the input sensor field device.
• an open on the input-signal wire or low-current portion of the input
sensor field device will not be detected, and will be seen as an
off/inactive input sensor field device.
• a shorted circuit from the sensor-power wire to sensor common (-V) is
detected as short fault (no voltage at the sensor-power port).
• a shorted circuit from the sensor-power wire to the input-signal wire
cannot be detected. It will appear as an on/active input device.
• a shorted circuit from the input-signal wire to sensor common (-V), with
the input sensor field device in the off-state, cannot be detected. It will
appear as an off/inactive input sensor device.
• a shorted circuit from the input-signal wire to sensor common (-V), with
the input sensor field device in the on-state, is detected as a short fault if
the sensor field device can pass the sensor power short circuit current.
• a shorted 3-wire input sensor device may or may not be detected,
depending on which portion of the input sensor device is shorted.
• a shorted circuit to the DIN rail or chassis ground cannot be detected.
Diagnostic Functions for the 1794-IB16D
Each unused sensor port requires a dummy resistor to mask the channel
diagnostic function.
Open OFF or ON OFF Red Red Open wire
& Module No current in Sensor Power terminal-
Missing sensor, cut Sensor Power or Input Signal wire
Short OFF OFF Red Red Short & Module Shorted Sensor Power/ Common
OFF ON OFF Yellow None Shorted Sensor Power/ Input Signal
OFF OFF OFF OFF None Shorted Input Signal/ Common
ON OFF Red Red Short & Module
Shorted Input Signal/ Common
1
Reverse
User
Power OFF or ON OFF Red OFF Reverse & Module User power supply wiring is reversed
1 If sensor can pass Sensor Power short circuit current
Fault Device/Input State Indicators Error Bit
Status Conditions
Field
Device Input
Status Module
Fault Channel
Fault
Open OFF OFF Red Red Open wire
&
Module No current in Sensor Power terminal-
Missing sensor, cut Sensor Power or
Common wire
OFF or ON OFF OFF OFF None Cut Input Signal wire
Short OFF OFF Red Red Short & Module Shorted Sensor Power/ Common
OFF ON OFF Yellow None Shorted Sensor Power/ Input Signal
OFF OFF OFF OFF None Shorted Input Signal/ Common
ON OFF Red Red Short & Module Shorted Input Signal/ Common 1
Reverse User Power OFF or ON OFF Red OFF Reverse & Module User power supply wiring is reversed
1 If sensor can pass Sensor Power short circuit current