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FB MON Bit 2

Monitoring Discrepancy Error - Secure Input Group

Beckhoff · TwinSAFE Logic FB

¿Qué significa FB MON Bit 2 ?

A discrepancy has been detected between the 'Secure1' and 'Secure2' input channels in the FB MON function block. These inputs are used to switch off the evaluation of 'MonIn(x)' inputs. A discrepancy here means the redundant secure inputs are not in agreement, which can lead to unintended disabling of monitoring functions, potentially bypassing safety.

Causas comunes

  • Discrepancy between the 'Secure1' and 'Secure2' enable signals (e.g., from a mode selector switch) due to one signal being active and the other inactive.
  • Faulty external device providing the 'Secure' signals, such as a mode selector switch with worn or damaged redundant contacts.
  • Intermittent connection or wire break on one of the 'Secure' input lines (e.g., terminal X12.1 or X12.2).
  • Incorrect configuration of the 'Secure' input type (e.g., NC vs NO) in the safety controller parameters (e.g., P_SECURE_INPUT_LOGIC).
  • Unintended activation or deactivation of one 'Secure' input due to external wiring fault or component failure.

Pasos de reparación & Lista de verificación

Haga clic en los pasos para seguir su progreso.

  1. 1

    Identify the external source of the 'Secure1' and 'Secure2' signals (e.g., key switch S_MODE) and test its redundant contacts for proper operation using a multimeter.

  2. 2

    Measure the voltage potential on the 'Secure1' and 'Secure2' input terminals of the safety controller in both desired states (e.g., 24VDC when active, 0VDC when inactive).

  3. 3

    Verify continuity of the wiring from the source device's redundant contacts to the safety controller's 'Secure1' and 'Secure2' input terminals.

  4. 4

    Check the safety controller's parameter settings for the 'Secure Input Group' (e.g., P_MON_SECURE_TYPE, P_MON_SECURE_DEBOUNCE) to ensure they match the physical wiring and application.

  5. 5

    Observe the diagnostic status of 'Secure1' and 'Secure2' inputs through the safety controller's software interface to determine which input is causing the discrepancy.

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Datos técnicos verificados. Última actualización: March 2026

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Fuente: Beckhoff TwinSAFE Logic FB