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Functional description

The SF_ModeSelector function block evaluates the function of a mode selector switch with up to eight positions. A mechanical mode selector switch can be used to set a specific operating mode (e.g., service mode, setup mode, cleaning mode, etc.). Each operating mode can have a different safety-related function.

The selected operating mode is specified by a SAFETRUE signal at one of the inputs S_Mode0 to S_Mode7. If all the relevant conditions are fulfilled, the function block outputs the selected operating mode via a SAFETRUE signal at the corresponding output (S_Mode0Sel to S_Mode7Sel).

The function block executes stop category 0 at its output.

Automatic/Manual confirmation of operating mode acceptance

AutoSetMode is used to specify whether acceptance of the operating mode set at the inputs (S_Mode0 to S_Mode7) takes place automatically (AutoSetMode = TRUE). Manual confirmation is required (via a SAFEFALSE > SAFETRUE edge at the S_SetMode input) if AutoSetMode is set to FALSE.

Automatic acceptance of the set operating mode (AutoSetMode = TRUE) must only be used if it is certain that starting up the machine/system will not lead to a hazardous situation or that a start-up will be prevented in a suitable manner at another location or using other means.

WARNING
Unintended machine operation
  • Verify the impact of an automatic acceptance of the set operating mode on your machine or process prior to implementation.
  • Observe the regulations given by relevant sector standards regarding the automatic acceptance of the set operating mode.
  • Verify that a suitable start-up inhibit is in place at another location or using other means.

Time slot for switching operation

For mechanical reasons, all contacts are opened simultaneously for a short period during switching of the mode selector switch. ModeMonitorTime is used to specify a time slot within which the switching operation of the mode selector switch must be completed. All inputs can be SAFEFALSE during this time. Afterwards, the function block detects this as an error (output Error = TRUE).

Note
If several inputs S_Mode0 to S_Mode7 are SAFETRUE at the same time during the switching operation, an error message is output immediately (output Error = TRUE and S_Mode0Sel to S_Mode7Sel = SAFEFALSE), independent of the monitoring time set at ModeMonitorTime.

Locking the set operating mode to prevent changes

The S_Unlock input supports locking of the function block to prevent the set operating mode being changed. This involves generating a SAFEFALSE signal (using a key switch, for example). In this case, modifications at inputs S_Mode0 to S_Mode7 do not cause the operating mode to modify. This means that turning the mode selector switch has no effect.

The input signals are only evaluated for permissible signal combinations (only one input SAFETRUE at the same time, not all inputs SAFEFALSE) if the operating mode switchover is not locked with S_Unlock = SAFEFALSE.

WARNING
Non-conformance to safety function requirements
  • Verify the impact of a locked mode selector switching on your machine or process prior to implementation.
  • Make certain that appropriate procedures and measures (according to applicable sector standards) have been established to help avoid hazardous situations when the operating mode switchover is locked by S_Unlock = SAFEFALSE.

The function block outputs a signal combination at its outputs in accordance with the operating mode requested at the inputs. However, the function block itself cannot ensure that the operating mode selected is actually executed by the application. This means you are responsible for ensuring that the signals output by the function block are connected and processed correctly, in accordance with the safety integrity level for the operating mode selected.

WARNING
Unintended machine operation

Make certain that the signals output by the function block are connected and processed correctly according to the safety integrity level for the selected operating mode.