Table Of Contents

Fault Response Time

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    Last Modified: September 6, 2017

    Fault diagnostics run parallel to and independent of the application processes. Faults used as transition conditions in the state machine diagram require the time necessary for fault processing and application processing to set an output response.

    • User-configurable diagnostics used as transition conditions: Fault response time = Diagnostic response time + Application processing time + Output signal response time

    Fault response time will vary depending on the execution path defined in the User Program. If the fault triggers a state that sets an output, only one iteration of the application processing time will elapse. Otherwise, the application processing time will increase by the number of states and associated transitions through which the User Program cycles to fully react to the fault.

    Figure 1. Response Time for Faults Used in Transitions

    Faults set to Fail-safe and automatic self-diagnostics do not require the application processing time. After the fault response time elapses, the module transitions into Fail-safe Mode.

    • Automatic self-diagnostics: Fault response time = Diagnostic response time + Output signal response time
    • User-configurable diagnostics set to Fail-safe: Fault response time = Diagnostic response time + Output signal response time
    Figure 2. Fail-Safe Response Time

    Refer to the Diagnostic Response Time Specifications to determine the diagnostic response time for your application.


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