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• Safety FBs in PLCopen_SF_V2_00 Library
• SF_Antivalent
• Functional description

Functional description

The safety-related SF_Antivalent function block monitors the signals of two safety-related inputs on the Sicherheitssteuerung for different signal states. Typically, these signals come from two-channel sensors or switches such as an emergency-stop control device.

The result of the signal comparison procedure is shown at the S_AntivalentOut function block output. The S_AntivalentOut output becomes SAFETRUE when the function block is activated (Activate = TRUE), has not detected an error (Error = FALSE) and the S_ChannelNC and S_ChannelNO inputs switch as follows within the time set at DiscrepancyTime:
S_ChannelNC from SAFEFALSE to SAFETRUE and
S_ChannelNO from SAFETRUE to SAFEFALSE.

As soon as S_ChannelNC = SAFEFALSE and/or S_ChannelNO = SAFETRUE, the discrepancy time measurement starts automatically. Both inputs may have the same states during the set discrepancy time. After that time, the function block detects this as an error (Error output becomes TRUE and S_AntivalentOut switches to SAFEFALSE as a result).

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

WARNUNG

Unintended machine operation Verify that the S_AntivalentOut 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.

Hinweis Permanent signals (S_ChannelNC = SAFETRUE and S_ChannelNO = SAFEFALSE) at the inputs when the function block is activated (Activate = TRUE) or when the Sicherheitssteuerung is started up switch the enable signal (S_AntivalentOut) to SAFETRUE.

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, you must always connect the two inputs to different contact types (1 x N/C contact, 1 x N/O contact).

Hinweis The discrepancy time is exceeded if the same states are present at the inputs once the set duration has elapsed. This results in an error message (Error output = TRUE). The S_AntivalentOut output is then SAFEFALSE, irrespective of the states at the inputs. In such cases, the error must be "reset" by switching input S_ChannelNC to SAFEFALSE and input S_ChannelNO to SAFETRUE.

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.