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POINT I/O 24V DC 4-channel Discrete Input Module with Diagnostics
Publication 1734-IN029B-EN-E - July 2018
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 LED indicator of the input 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 EDS file of the module, 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' 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.
