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Fault Latching

    Last Modified: September 6, 2017

    C Series Functional Safety modules latch detected faults. Fault latch time is programmable on the Module and Diagram tab of the configuration pane. C Series Functional Safety modules have a single fault latch timer which resets for any fault.

    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 LabVIEW, set the fault latch time larger than the Scan Interface scan rate.


    If the module changes operating modes, test pulse faults, readback faults, and discrepancy faults will clear after the fault latch time expires. If you set these faults to trigger Fail-safe mode, the faults could clear before you can read which fault. To make sure you can read these faults, do the following:

    • Set the fault latch time long enough to read it in your LabVIEW program.
    • Program LabVIEW to latch the data.

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