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Fault Latching

    Last Modified: May 15, 2018

    C Series Functional Safety modules latch detected faults. Fault latch time is a programmable parameter on the Module and Diagram tab of the configuration pane.

    The NI 9350 has a single fault latch timer which resets for any fault.

    The NI 9351 has two fault latch timers. One for digital faults and one for analog faults. The fault latch time parameter applies to both fault timers. Digital faults will not reset the analog fault time and analog faults will not reset the digital fault time.

    Figure 1. Fault Latch Time on Discrepancy Faults

    Latched faults persist until the configured latch time has elapsed. Detected faults will remain latched when the operational mode changes from Verification Mode to Operational Mode or from Operational Mode to Verification Mode. When the User Program restarts, a latched fault from the previous mode can trigger Fail-safe Mode or transition the User Program to a new state.


    To monitor faults through Scan Interface, set the fault latch time larger than the Scan Interface scan rate.

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