Introduction

The BMXSRA0405 safety digital output relay module provides the following diagnostics using its T_U_DIS_SIS_OUT_4 device DDT elements:

  • output contact diagnostics

  • internal error detection

Output Contact Diagnostics

Depending on the application number that has been configured for the module, the module can automatically test its ability to toggle the output contact states (from ON to OFF, or OFF to ON) for a time too short to cause an actuator response. If the channels does not successfully toggle between energized and de-energized, the CH_HEALTH bit in the T_U_DIS_SIS_CH_ROUT DDDT structure is set to 0, indicating it is not operational.

NOTE: Application numbers 2, 4, 6, and 8 perform this automatic signal test. Application numbers 1, 3, 5, an 7 do not, and therefore require a daily manual transition of the output channel state to confirm its operability.

Output Command Diagnostics (Internal Error Detection)

The relay command is processed using two separate, parallel circuits. The values of the circuits are compared. If the compared values are different, the channel is determined to be non-operational and the IC bit in the T_U_DIS_SIS_CH_ROUT DDDT structure is set to 1.

Refer to the architecture diagram for the BMXSRA0405 safety digital output relay module for a visual presentation of this process.