Introduction

The BMXSDI1602 safety digital input module provides the following diagnostics using its T_U_DIS_SIS_IN_16 device DDT elements:

  • input diagnostics

  • internal error detection

  • channel wiring diagnostics

  • overvoltage and undervoltage diagnostics

Input Diagnostics

Each input channel is tested for operational effectiveness at the start of every cycle (or scan). Each channel is forced to the energized state and tested to check that the energized state was achieved. Then the channel is forced to the de-energized state and again is tested to check that the de-energized state was achieved.

If the channel does not successfully toggle between energized and de-energized, the CH_HEALTH bit in the T_U_DIS_SIS_CH_IN DDDT structure is set to 0 indicating it is not operational.

Internal Error Detection

Each cycle, the module performs an input diagnostic sequence. The module processes the input value using two separate, identical circuits. The two values are compared to determine if an internal error exists in the module internal process. If the compared values are different, the IC bit in the T_U_DIS_SIS_CH_IN DDDT structure is set to 1 indicating it is not operational.

Refer to the architecture diagram for the BMXSDI1602 safety digital input module for a visual presentation of this process.

Channel Wiring Diagnostics

The wiring of the sensor to the input channel can be continuously diagnosed for any of the following conditions:

  • cut wire (open circuit)

  • short circuit to 24 Vdc

  • short circuit to 0 Vdc

  • cross circuit between two parallel channels

The availability of these diagnostics depends on the power source employed by the specific wiring design, and on the diagnostic function being enabled in the configuration page of the module.

If one of these conditions is detected, the T_U_DIS_SIS_CH_IN DDDT structure sets the associated bit value to 1, as follows:

  • the OC bit is set to 1 if an open (cut) wire or short circuit to 0 Vdc ground condition is detected.

  • the SC bit is set to 1 if a short circuit to the 24 Vdc source or cross circuit between two channels is detected.

Overvoltage and Undervoltage Diagnostics

The module continuously tests for an overvoltage and an undervoltage condition. The following threshold values apply:

  • Undervoltage threshold = 18.6 Vdc

  • Overvoltage threshold = 33 Vdc

If either condition is detected, the module sets the PP_STS bit in the T_U_DIS_SIS_IN_16 device DDT to 0.