Functional description

This function block monitors two signals of a connected two-channel sensor or switch for the same signal states (equivalence).

As soon as one of the inputs switches its state, discrepancy time monitoring starts automatically. Both inputs may have different states during the set discrepancy time. After that time, the function block detects this as an error (Error output becomes TRUE, S_EquivalentOut switches to SAFEFALSE as a result).

The result of the signal comparison procedure is shown at the S_EquivalentOut function block output. The S_EquivalentOut output becomes SAFETRUE when the function block is activated (Activate = TRUE), has not detected an error (Error = FALSE) and the S_ChannelA and S_ChannelB inputs both have the state SAFETRUE within the time set at DiscrepancyTime.

The function block supports a safety-related monitoring function but not a safety-related control function.

WARNUNG

Unintended machine operation

Verify that the S_EquivalentOut enable signal does not directly control the safety process.

Validate the overall safety-related function, including the start-up behavior of the process, and thoroughly test the application.

The function block executes stop category 0 at its interface.

Hinweis
The switchover from SAFEFALSE to SAFETRUE is monitored for both inputs, as well as the switchover from SAFETRUE to SAFEFALSE. Therefore, always connect both inputs symmetrically, either to N/C contacts or N/O contacts.

Hinweis
The discrepancy time is exceeded if different states are present at the inputs once the set duration has elapsed. This results in an error message (Error output = TRUE). The S_EquivalentOut output is then SAFEFALSE, irrespective of the states at the inputs. In such cases, the error must be "reset" by setting both inputs to the SAFEFALSE state.

Hinweis
Cross-circuit monitoring is not performed by the function block. It is your responsibility to perform this monitoring function outside of this function block in the safety-related control system.