NX I/O Output Under Fault Condition
Written by Daniel Heslewood
Updated at April 6th, 2025
By default, NX-IO and expansion cards are configured to switch the output channels or bits to zero when a watchdog error, or a major fault is detected on the CPU unit / Communications Coupler. There are many scenarios where this behavior is not ideal and can cause disruptions to a particular process.
This article will explain what settings are associated with this behavior, and how to change them in Sysmac Studio.
Load Rejection Output Setting is a function whose purpose is to maintain a set output status, by executing the preset output operation when a unit cannot receive output data due to an error. Below are some examples on how you may change this on different units.
For CPU's with built-in I/O
The settings for built-in I/O can be found under Controller Setup → Built-in I/O Settings, from the Multiview Explorer. With the Built in I/O Settings open, scroll down to the Load Rejection Output Settings.
Outputs can be set to either Turn OFF the output, or Hold the present value under fault conditions.
For NX additional I/O
Here we are referring to I/O that is gained from additional NX Units mounted to the PLC.
The process to change the Load Rejection Output Settings is the same for all units, however, the effect that the load rejection setting has can differ between units. Be sure to refer to the manual for the specific NX Unit for the settings and their meanings.
To access the Load Rejection Output Settings:
Right click on the relevant NX unit under either the CPU/ Expansion rack or the EtherCAT coupler node, and select Edit. This will bring up all parameters for the unit.
Here are some examples of what the load rejection output settings may look like for different NX-IO units. Not all units are covered, information for a specific unit can be found in the user manual for the unit under the Functions section.
Digital Output
Applicable Units:
- All NX digital output units.
The setting method varies between cards, for two and four-point cards, the Load Rejection setting is set as TRUE/ FALSE for the respective bits.
For eight-point cards to 32-point cards, this is set by writing a Hex value to the parameter.
Two-point / 4-point units.
8-point/ 16-point/ 32-point units.
Analog I/O
Applicable Units:
- All NX Analog output units.
The output value of an Analog output unit can be set to any of the following when an error occurs.
Temperature Control
Applicable Units:
- All NX Temperature Control Units
- NX-TC[]
In this case, the Load Rejection Output Settings, refers to the Manipulated variable to output under a fault condition.
This function is only enabled during PID control .
