Find and Fix I/O Problems

Diagnostic digital modules detect faults and report back.


System designers and end users want to minimise the time it takes to find and fix field device and power supply problems. Using Rockwell Automation FLEX I/O eliminates long wiring runs and reduces terminations per point. But monitoring the condition of I/O and identifying the source of any system failure can be a challenge. Detecting open wire, short circuit and reverse polarity of external power can be tough if you're not right next to the device.

New FLEX I/O diagnostic digital modules (1794-IB16D and 1794-OB16D) detect such faults and report them back to the controller. Once there, they can be monitored via operator panels or a human machine interface (HMI) located remotely.


The FLEX diagnostic modules detect faults such as open/missing input or output field devices or wiring, shorted output field devices, shorted input or output wiring and reverse polarity of user power supply wiring. While they do not check for the presence of the user-supply voltage, this is most easily done by directly wiring the supply voltage to an input channel.
The diagnostic output module (OB16D) is internally protected against damage from a shorted output field device or shorted output wiring. It is also internally protected against output overloads and automatically resets itself when the shorted or overload condition is removed.


Troubleshooting a faulted system is simple. At the module, a red LED indicates that the module has detected a fault. A red/yellow LED for each channel identifies which channel is experiencing a fault. Further detail of the fault is given in the module's status word. The "module error" bit is set with any fault, and the "short", "open" or "reverse polarity" bit is set in response to the type of fault detected. For correct operation of the fault LEDs and the module's status bits, load resistors must be employed with unused input and output channels. In addition, leakage resistors are needed on input channels that use hard contacts (mechanical switch or relay contacts).


Diagnostic modules can be used with any Rockwell Automation controller product that operates with FLEX I/O. They have 16 channels and are compatible with all of the FLEX I/O adapters. They communicate on EtherNet/IP, ControlNet, DeviceNet, Remote I/O and many other networks. Modular electronic data sheets for these modules are available in RSNetWorx 5 for DeviceNet. The 1794-IB16D module must be used with the 32-point 1794-TB32 or 1794-TB32S terminal base. The 1794-OB16D can use the more standard 1794-TB3 terminal base, as well as the 1794-TB3S and 1794-TB2.