Additional application example

This section describes an additional possible application, where the function block evaluates a three-stage enable switch.

The function block must only be used in an actual application once a risk analysis has been conducted.

Details of the risk category/SIL/PL have not been included here, as clas­sification is always based on the application in which the function block is used.

Evaluating a three-stage enable switch. Confirming the selected operating mode using SF_ModeSelector.

This example describes the evaluation of a three-stage enable switch by the SF_EnableSwitch function block. The enable switch is used to manually confirm an operating mode of a machine. The operating mode is selected by means of a three-stage mode selector switch S1, which is evaluated using the safety-related SF_ModeSelector function block.

In order to operate the controlled machine in operating mode 2 (in the example shown, this is setup mode) or 3 (manual mode), the selected mode must be enabled manually by pressing the enable switch.

Connecting the SF_EnableSwitch function block:

• The function block is perpetually activated by the TRUE constant at the Activate input.

• The enable switch S5 is connected to input terminals I5 and I6 of the safety-related input device SDI 1. The signal of input terminal I5 is assigned to the global I/O variable S5_SwitchCH1_In, which in turn is connected to the function block input S_EnableSwitchCh1. The signal of input terminal I6 is assigned to the global I/O variable S5_SwitchCH2_In, which in turn is connected to the function block input S_EnableSwitchCh2.

• The selected operating mode is confirmed at input S_SafetyActive of the SF_EnableSwitch function block in the form of a feedback signal issued by the speed monitor, see note below.

• A restart inhibit is set via S_AutoReset of the SF_EnableSwitch function block. This inhibit becomes active after a valid signal sequence returns at the function block inputs S_EnableSwitchCh1 and S_EnableSwitchCh2. The Reset button S4 for removing the restart inhibit is connected to input terminal NI0 of the standard input device DI 1. The reset signal is assigned to the global I/O vari­able S4_Reset. The reset button resets error states for both func­tion blocks.

Connecting the SF_ModeSelector function block:

• The constant TRUE at the Activate input also causes the safety-related SF_ModeSelector function block to be permanently activated.

• The mode selector switch S1 to be evaluated is connected to the three input terminals I0, I1 and I2 of the safety-related input device SDI 1. The signals are assigned to the global I/O variables and the function block inputs are connected as follows:

  Terminal	Global I/O variable	Function block input
  I0	S1_State0_In	S_Mode0
  I1	S1_State1_In	S_Mode1
  I2	S1_State2_In	S_Mode2

• A key switch S2 is connected to input terminal I3 of the safety-related input device SDI 1. The signal is assigned to the global I/O variable S2_LockMode_In, which in turn is connected to the S_Unlock input of the SF_ModeSelector function block. Locking the key switch (S_Unlock = SAFEFALSE) locks the oper­ating mode that has been set.

• The AutoSetMode input is switched to FALSE, which means that manual confirmation of the set operating mode is required at the S_SetMode input. A button S3 is connected to the input terminal I4 of the safety-related input device SDI 1 for this purpose. The signal is assigned to the global I/O variable S3_SetMode_In, which in turn is connected to the function block input S_SetMode.

• The signal of reset button S4 connected to input terminal NI0 of the standard input device DI1 is used for resetting error messages and removing the active restart inhibit (positive signal edge at the Reset function block input). The global I/O variable S4_Reset is assigned to the function blocks SF_EnableSwitch and SF_ModeSelector.