Rockwell Automation 1738-IB4DM12 ArmorPoint 24V dc 4-channel Digital Input Module with Diagnostics I.I. - Manual (Page 6)

Publication 1738-IN021A-EN-E - January 2007
6 ArmorPoint 24V dc 4-channel Digital Input Module with Diagnostics
Understand Short-circuit
Detection The sensor source voltage (SSV) for each input is protected against short
circuits. For currents above 200 mA, a fault signal is issued and the input LED
indicator is illuminated solid red. A thermally-actuated smart-power device or
PTC is used as the protection means. On a per-input basis, the circuit and
produced data automatically reset and SSV energizes upon removal of the
short circuit. An individual fault signal is issued for each shorted SSV
condition.
The shorted input LED indicator illuminates red to denote short-circuit fault
status.
See the section on interpreting LED indicators for related information.
When the SSV is loaded to the maximum rated current of 50 mA, a voltage
drop of as much as 2.5V dc can exist between the user auxiliary power and the
SSV connection. For example, for a supply of 10V dc to a sensor with power
derived from the SSV, a supply of 12.5V dc is needed at the auxiliary power
connection.
Understand Open-wire
Detection Sensor source voltage (SSV) current for each input is monitored. Monitoring is
accomplished in the SSV leg to accommodate the largest number of sensors
possible. For currents below 0.5 mA, a fault signal is issued and the input's
LED indicator blinks red. On a per-input basis, the circuit and produced data
automatically reset upon removal of the open-wire condition. See the
information about interpreting LED indicators for related information.
By using a configuration tool, you can disable the open- wire diagnostics on an
input-point basis to keep unused input indicators from turning red and
signaling a fault when an input is not in use. Enabling or disabling input-point
level open-wire diagnostics is implemented via the module’s EDS file, GSD
file, or Logix profile and its firmware.
You can also disable all the open-wire diagnostics, using a single entry via the
software user interface. The default configuration has all four input channels’s
open-wire indication enabled.
If a sensor with a dry contact output is used, wire one side of the contact to
the SSV terminal for the corresponding input. Wire the other side of the
contact to the input. Additionally, place a shunt resistor in parallel with the
contact, at the sensor, to cause greater than 0.5 mA to be drawn through the
SSV terminal at all times.