Rockwell Automation 1794-OB16D FLEX I/O Diagnostic Modules User Manual - Manual (Page 106)

Publication 1794-UM061A-EN-P - July 2006
104 Interpret the Indicators
1794-IB16D Diagnostic
Functional Details
The 1794-IB16D input module provides 16 points of 24V dc sinking input
with open wire and short circuit diagnostic features. Each input signal has an a
associated sensor power connection. The module monitors current and
voltage at each input channel sensor power terminal.
Two module indicators and four diagnostic bits report fault conditions:
• the module Fault indicator and the individual faulted channel indicator
also turn red under open and short conditions.
• the module Fault indicator turns red for reverse user power conditions.
• the open bit is set for open sensor and wiring conditions.
• the short bit is set for shorted sensor and wiring conditions.
• the reverse power bit is set for reverse polarity user power conditions.
• the module fault bit is set for any open, short or reverse power
conditions detected.
Diagnostic Capabilities
The module’s diagnostic capability depends on the connected sensor type.
For 2-wire sensors and contact input devices (for example, switches):
• an open fault will be detected when an open occurs on either the
sensor-power wire, the input signal wire, or the input sensor field device.
• a shorted circuit from a sensor-power wire to common fault (-V) is
detected as a 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 appears as an on/active input device.
• a shorted circuit from the input-signal wire to common (-V), with the
input sensor field device in the off-state (field device contacts open),
cannot be detected. It appears as an off/inactive input sensor device.
• a shorted circuit from the input-signal wire to common (-V), with the
input sensor field device in the on-state (field device contacts closed), is
detected as a short fault if the sensor field device can pass the sensor
power short circuit current.
• a shorted 2-wire input sensor field device (contact field device) cannot
be detected. It appears as an on/active input field device.
• a shorted circuit from a sensor-power wire, an input sensor wire, or the
input-sensor field device to the DIN rail or chassis ground cannot be
detected.
A dummy resistor must be placed across the contacts of contact input devices
(for example, switches). Use 20 K
Ω resistors.
Fault Device State Fault Indicators Error Bit
Status Conditions
Field Device Input Status Module Fault Channel
Fault