SF_ModeSelector

Help version 2.0 / Issue date: 2024.03
The following description is valid for the function block SF_ModeSelector_V2_0z, Version 2.0z (where z = 0 to 9).

Short Description The safety-related SF_ModeSelector function block evaluates the states 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.

Block Icon

Inputs Activate

Short description Value

State-controlled input for activating the function block.
Data type: BOOL
Initial value: FALSE

FALSE: Function block inactive.

TRUE: Function block activated.

Refer to the topic "Activate" for details.

S_Mode0 to S_Mode7

Short description Value

State-controlled inputs for the status of the connected mode selector switch. There must only ever be one SAFETRUE signal at one of the inputs.
Data type: SAFEBOOL
Initial value: SAFEFALSE
If more than one operating mode is detected at the mode selector switch, this behavior immediately leads to an error. If no operating mode is selected (S_Mode0 to S_Mode7 = SAFEFALSE), this leads to an error after the time set at ModeMonitorTime has elapsed.

Note
If the set operating mode is locked by S_Unlock = SAFEFALSE, the signal combination at the inputs (S_Mode0 to S_Mode7) is not evaluated.

SAFEFALSE: Operating mode not selected

SAFETRUE: Operating mode selected

Refer to the topic "S_Mode0 to S_Mode7" for details.

S_Unlock

Short description Value

State-controlled input for locking/unlocking mode selector switching (S_Mode0 to S_Mode7) with, for example, a key switch.
Data type: SAFEBOOL
Initial value: SAFEFALSE

SAFEFALSE: Operating mode switchover disabled

SAFETRUE: Operating mode switchover possible

Refer to the topic "S_Unlock" for details.

S_SetMode

Short description Value

Edge-triggered input for confirming or enabling the operating mode set at S_Mode0 to S_Mode7.
Data type: SAFEBOOL
Initial value: SAFEFALSE
Manual confirmation is required (via a SAFEFALSE > SAFETRUE edge at the S_SetMode input) if AutoSetMode is set to FALSE.

SAFEFALSE: Manual enabling of the set operating mode not requested

Edge SAFEFALSE > SAFETRUE: Manual enabling of the operating mode set at S_Mode0 to S_Mode7

Refer to the topic "S_SetMode" for details.

AutoSetMode

Short description Value

State-controlled input for specifying the automatic acceptance of the operating mode set at inputs S_Mode0 to S_Mode7.
Data type: BOOL
Initial value: FALSE

Note
If the set operating mode is locked by S_Unlock = SAFEFALSE, no switchover to another operating mode is performed.

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.

FALSE: The set operating mode is not accepted automatically. Manual confirmation is required via a positive edge at the S_SetMode input.

TRUE: The set operating mode is accepted automatically. This assumes that

the function block is activated (Activate = TRUE)

and no error is reported (Error = FALSE)

and mode selector switching not being locked (S_Unlock = SAFETRUE).

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.

Refer to the topic "AutoSetMode" for details.

ModeMonitorTime

Short description Value

Input for specifying the maximum permissible switchover time for switching the operating mode.
Data type: TIME
Initial value: #0ms
All inputs may show a SAFEFALSE signal simultaneously during the time set at ModeMonitorTime. After this, a simultaneous SAFEFALSE signal at S_Mode0 to S_Mode7 leads to an error (Error = TRUE).
If more than one operating mode is detected at the mode selector switch, this behavior immediately leads to an error. Enter a time value according to your risk analysis.

WARNING

Non-conformance to safety function requirements

Verify that the time value set at ModeMonitorTime corresponds to your risk analysis.

Be sure that your risk analysis includes an evaluation for incorrectly setting the time value for the ModeMonitorTime parameter.

Validate the overall safety-related function with regard to the set ModeMonitorTime value and thoroughly test the application.

Refer to the topic "ModeMonitorTime" for details.

Reset

Short description Value

Edge-triggered input for the reset signal:
Resetting error messages when the cause of the error is no longer present.
Resetting an error by means of a positive signal edge at the Reset input can cause the S_Mode0Sel to S_Mode7Sel output to switch to SAFETRUE immediately (depending on the status of the other inputs).
Refer to the warning below this table.
Data type: BOOL
Initial value: FALSE

Note
Resetting does not occur with a negative (falling) edge, as specified by standard EN ISO 13849-1, but with a positive (rising) edge.
To implement the reset with a falling edge (with regard to the mandatory acceptance procedure), use the safety-related function block SF_Reset.

FALSE: Reset is not requested

Edge FALSE > TRUE: Reset is requested

WARNING

Unintended start-up

Include in your risk analysis the impact of the reset by means of a positive signal edge at the Reset input.

Make certain that appropriate procedures and measures (according to applicable sector standards) have been established to help avoid hazardous situations when resetting.

Do not enter the zone of operation when resetting.

Ensure that no other persons can access the zone of operation when resetting.

Use appropriate safety interlocks where personnel and/or equipment hazards exist.

Refer to the topic "Reset" for details.

Outputs Ready

Short description Value

Output for signaling "Function block activated/not activated".
Data type: BOOL

FALSE: Function block is not activated (Activate = FALSE) and all outputs of the function block are switched to FALSE/SAFEFALSE.

TRUE: Function block is activated (Activate = TRUE) and the output parameters represent the state of the safety-related function.

Refer to the topic "Ready" for details.

S_Mode0Sel to S_Mode7Sel

Short description Value

Outputs for signaling the set operating mode.
There can only ever be one output showing a SAFETRUE signal at any one time.
Data type: SAFEBOOL

SAFEFALSE

One of the S_ModeXSel outputs = SAFEFALSE: The corresponding operating mode is not active.

All outputs (S_Mode0Sel to S_Mode7Sel) = SAFEFALSE: No operating mode is active

or the function block is not activated

or the error message is present.

SAFETRUE
One of the S_ModeXSel outputs = SAFETRUE:
The corresponding operating mode is active

and the function block is activated

and no error message is present.

Refer to the topic "S_Mode0Sel to S_Mode7Sel" for details.

S_AnyModeSel

Short description Value

Output for signaling whether a signal combination is output at the S_Mode0Sel to S_Mode7Sel outputs.

SAFEFALSE: Only SAFEFALSE signals are output at the S_Mode0Sel to S_Mode7Sel outputs.

SAFETRUE: A SAFETRUE signal is output at one of the S_Mode0Sel to S_Mode7Sel outputs to control a specific operating mode in the subsequent application.

Refer to the topic S_AnyModeSel for details.

SafetyDemand

Short description Value

Output for signaling "safety-related function requested".
This output displays whether the safety chain is interrupted and as a result, the attention of the operator is required.
Data type: BOOL

FALSE: Safety-related function is not requested.

TRUE: The safety-related function is requested.

Refer to the topic "SafetyDemand" for details.

ResetRequest

Short description Value

Output for signaling "reset is required".
This output indicates whether a reset by the operator is required.
Data type: BOOL

FALSE: No reset required.

TRUE: A reset is required:

to remove an active start-up or restart inhibit (if available for this function block)

or to reset an error.

Refer to the topic "ResetRequest" for details.

Error

Short description Value

Output for error message.
Data type: BOOL

FALSE: No error is present.

TRUE: The function block has detected an error. The S_ModeXSel output switches to SAFEFALSE as a result.

Refer to the topic "Error" for details.

DiagCode

Short description Value

Output for diagnostic message.
Data type: WORD Diagnostic message of the function block.
The possible values are listed and described in the topic "Diagnostic codes".

Refer to the topic "DiagCode" for details.

Detailed information Signal sequence diagram

The diagram shows the signal sequence for a valid operating mode switchover within the monitoring time set at ModeMonitorTime.

AutoSetMode = FALSE: Acceptance of the set operating mode requires manual confirmation via a positive edge at the S_SetMode input.

S_Unlock = SAFETRUE: Operating mode switchover is possible.

Note
The other signal sequence diagram can be taken into account.

0 The function block is not yet activated (Activate = FALSE).
As a result, all outputs are FALSE or SAFEFALSE.

1 The function block is activated (Activate = TRUE); the inputs are now evaluated.
The specification for operating mode 0 is present at the inputs (input S_Mode0 is SAFETRUE). However, as no manual confirmation for the operating mode switchover is detected at the S_SetMode input (this is necessary since AutoSetMode = FALSE), the S_Mode0Sel output remains SAFEFALSE in spite of the specification (S_Mode0 = SAFETRUE).

2 The mode selector switch is actuated, there is a request to switch to operating mode 7.
Input S_Mode0 becomes SAFEFALSE; this switch initiates measurement of the monitoring time.
S_Mode7 switches to SAFETRUE before the time set at ModeMonitorTime has elapsed. Although operating mode 7 has now been set as the new mode, it is not yet active, as a manual acceptance was specified with AutoSetMode = FALSE.
A positive edge is required at S_SetMode to activate the operating mode at the S_Mode7Sel output.

3 The positive signal edge at the S_SetMode input enables the set operating mode 7, and the S_Mode7Sel output becomes SAFETRUE.

Application example

This example uses a five-stage mode selector switch S1 to show how operating modes are selected.

The signals of the five N/O contacts of the mode selector switch are connected to the five input terminals 1.1 to 5.1 of safety-related input device PSDI 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

1.1 S1_M0_In S_Mode0

2.1 S1_M1_In S_Mode1

3.1 S1_M2_In S_Mode2

4.1 S1_M3_In S_Mode3

5.1 S1_M4_In S_Mode4

As a five-stage mode selector switch is evaluated, the function block inputs S_Mode5 to S_Mode7 remain unconnected.

A key switch S2 is connected to input terminal 6.1 of the safety-related input device PSDI 1. The input signal is assigned to the global I/O variable S2_Ulck_In, which in turn is connected to the S_Unlock input of the function block. Closing the key switch (S_Unlock = SAFEFALSE) locks the operating mode that has been set.

A FALSE constant is connected to the AutoSetMode input, which means that a manual confirmation of the set operating mode is required at the S_SetMode input. Button S3 is connected to input terminal 7.1 of the safety-related input device PSDI 1 for this purpose. Its input signal is assigned to the global I/O variable S3_SetM_In, which in turn is connected to the S_SetMode input of the function block.

A reset button S4, which is connected to input terminal 1.1 of the standard input device DI 1 is used for resetting error messages (positive signal edge at the Reset input of the function block). Its signal is assigned to the global I/O variable S4_Reset_MS, which in turn is connected to the Reset input of the function block.

Note
The S_Mode0Sel to S_Mode4Sel enable outputs of the SF_ModeSelector function block are connected to the inputs of other safety-related functions/function blocks. As a five-stage mode selector switch is evaluated, the function block outputs S_Mode5Sel to S_Mode7Sel are not relevant and can remain unconnected.

S1 Mode selector switch with 5 switch positions

S2 Key switch (blocking the mode selection)

S3 Confirmation

S4 Reset

See note above the illustration.

Further Info
The second application example and the accompanying notes can be taken into account.

Function block instantiation

The IEC 61131-3 standard defines function block instantiation. Instantiation means, a function block is defined once and can be used (instantiated) several times. This applies to all standard and safety-related FBs (local POUs as well as firmware and user library FBs).

Why instantiation?
A function block has an internal memory where it stores its own processing data (local variables). As a consequence, the output values calculated by the FB depend on the internally stored values. The same input values applied to an FB instance do not necessarily deliver the same results in another FB instance.
Therefore, it is necessary to store the internal data of the FB to a separated memory area each time the function block is processed, i.e., for each FB instance. To uniquely identify each FB instance and to clearly separate its memory area, instance names are used. The instance name of a function block has to be declared in the 'Variables' table of the POU where the FB is going to be used.

The following applies:

Function blocks can be instantiated in other function blocks or in program POUs. Calling FBs in function POUs is not possible.

Functions are called without instantiation because they do not have an internal memory.

Safety-related and standard (non-safety-related) code is strictly distinguished in PLCnext Engineer. If a Safety PLC is included in your project, the following applies:

Safety-related FBs can only be instantiated in safety-related POUs but not in standard (non-safety-related) POUs.

User-defined standard FBs can only be instantiated in standard POUs. They cannot be called in safety-related POUs.

Particular standard firmware FBs can be instantiated in both safety-related and standard POUs.

Note
When inserting a standard FB into a safety-related SNOLD network, the rules for implicit type conversion (safety-related to standard) apply.

Example for the instantiation of a safety-related PLCopen function block

The safety-related PLCopen function block 'SF_EmergencyStop_V2_00' was inserted into the project via a library. It is then available in the 'Programming' category of the COMPONENTS area. There is a folder with the same name as the library that provides the FBs for insertion into the safety-related code.
The FB is to be called twice in the code of the safety-related program 'S_Main' to evaluate the status of two safety-related emergency stop command devices. For each FB instance, an instance name is declared in the 'Variables' table of the calling program: EStop_M1 and EStop_M2. The FB instances have been inserted into the code worksheet, each instance with different variables connected to its input and output formal parameters.

Additional information is available in the following sections:

Functional description

Details of the application example

Fault avoidance

Implementation of safety requirements from applicable standards