SF_Equivalent

Tip

The version of the function block as described here corresponds to the latest version of the function block in Version list of function blocks.

Applicable safety standards

SF_Equivalent is a certified PLCopen function block. For detailed information about applied standards, see "PLCopen – Technical Committee 5 – Safety Software".

Important

The requirements listed in the standards must be fulfilled by the user.

Interface description

This function block links two equivalent SAFEBOOL inputs (both NO or NC) to a SAFEBOOL output under discrepancy time monitoring. This FB should not be used stand-alone since it has no restart interlock. It is required to connect the output to other safety related functionalities.

Table 14. VAR_INPUT

Name	Data Type	Initial Value	Description, parameter values
`Activate`	`BOOL`	`FALSE`	General input parameters
`S_ChannelA`	`SAFEBOOL`	`FALSE`	Variable Input `A` for logical connection `FALSE`: Contact `A` open `TRUE`: Contact `A` closed
`S_ChannelB`	`SAFEBOOL`	`FALSE`	Variable Input `B` for logical connection `FALSE`: Contact `B` open `TRUE`: Contact `B` closed
`DiscrepancyTime`	`TIME`	`T#0ms`	Constant Maximum monitoring time for discrepancy state of both inputs The `DiscrepancyTime` caution note must be observed.

DiscrepancyTime

For developers in Extended Level: The DiscrepancyTime input has to be set to a constant value. This means that the value must not be changed for the calls.

Table 15. VAR_OUTPUT

Name	Data Type	Initial Value	Description, parameter values
`Ready`	`BOOL`	`FALSE`	General output parameters
`S_EquivalentOut`	`SAFEBOOL`	`FALSE`	Safety-related output `FALSE`: At least one input signal = "`FALSE`" or status change outside of the watchdog time. `TRUE`: Both input signals are "active" and status change within watchdog time
`Error`	`BOOL`	`FALSE`	General output parameters

Figure 51. Function block: SF_Equivalent

Functional description

This function block links two equivalent SAFEBOOL inputs (both NO or NC) to a SAFEBOOL output under discrepancy time monitoring. The two A and B channels are interdependent. The output of the function block shows the evaluation result of both channels.

If the channel signal changes from TRUE to FALSE, the output immediately switches off (FALSE) for safety reasons.

Discrepancy time monitoring: The discrepancy time is the maximum period during which both inputs may have different states without the function block detecting an error. Discrepancy time monitoring starts when the status of an input changes. The function block detects an error when both inputs have different states once the discrepancy time has elapsed.

Both inputs must be switched symmetrically. This means that monitoring is performed for both inputs for switching from TRUE to FALSE as well as for switching from FALSE to TRUE.

Table 16. Logic table of inputs/outputs

Inputs				Outputs
`Activate`	`S_ChannelNCS`	`S_ChannelNO`	`DiscrepancyTime`	`Ready`	`S_EquivalentOut`	`Error`	`DiagCode`
`FALSE`	`FALSE`	`TRUE`	Not started	`FALSE`	`FALSE`	`FALSE`	`0000`
`TRUE`	`FALSE`	`FALSE`	Not started	`TRUE`	`FALSE`	`FALSE`	`8001`
`TRUE`	`TRUE`	`FALSE`	Started	`TRUE`	`FALSE`	`FALSE`	`8004`
`TRUE`	`TRUE`	`FALSE -> TRUE`	Started	`TRUE`	`TRUE`	`FALSE`	`8000`
`TRUE`	`TRUE`	`TRUE`	Not started	`TRUE`	`TRUE`	`FALSE`	`8000`
`TRUE`	`TRUE`	`TRUE -> FALSE`	Started	`TRUE`	`FALSE`	`FALSE`	`8005`
`TRUE`	`TRUE -> FALSE`	`FALSE`	Started	`TRUE`	`FALSE`	`FALSE`	`8001`
`TRUE`	`FALSE`	`FALSE -> TRUE`	Started	`TRUE`	`FALSE`	`FALSE`	`8014`
`TRUE`	`FALSE -> TRUE`	`TRUE`	Started	`TRUE`	`TRUE`	`FALSE`	`8000`

Tip

In the logic table, an arrow (->) stands for a transition. TRUE -> FALSE means that the value of the variable has changed from TRUE to FALSE.

Status diagram

Figure 52. Status diagram: SF_Equivalent

Tip

Note: The transition from any state to the Idle state, initiated by Activate = FALSE, is not shown. In every case, these transitions have the highest priority.

Figure 53. Timing diagram 1: SF_Equivalent

Error detection

The function block monitors the discrepancy time between channel Channel A and channel Channel B, when switching to TRUE as well as switching to FALSE.

Error behavior

S_EquivalentOut is set to FALSE. Error is set to TRUE. DiagCode displays the error status. There is no Reset defined as an input coupled with the reset of an error. As soon as a Set of input values with the correct S_EquivalentOut is present, Error is FALSE again.

FB-Specific Error and Status Codes

Table 17. FB-specific error codes

`DiagCode`	Statue Name	Status description and output setting
`16#C001`	`Error 1`	Discrepancy time expired in status `8004` `Ready = TRUE` `S_EquivalentOut = FALSE` `Error = TRUE`
`16#C002`	`Error 2`	Discrepancy time expired in status `8014` `Ready = TRUE` `S_EquivalentOut = FALSE` `Error = TRUE`
`16#C003`	`Error 3`	Discrepancy time expired in status `8005` `Ready = TRUE` `S_EquivalentOut = FALSE` `Error = TRUE`

DiagCode

Statue Name

Status description and output setting

16#C001

Error 1

Discrepancy time expired in status 8004

Ready = TRUE

S_EquivalentOut = FALSE

Error = TRUE

16#C002

Error 2

Discrepancy time expired in status 8014

Ready = TRUE

S_EquivalentOut = FALSE

Error = TRUE

16#C003

Error 3

Discrepancy time expired in status 8005

Ready = TRUE

S_EquivalentOut = FALSE

Error = TRUE

Table 18. FB-specific status codes

`DiagCode`	Statue Name	Status description and output setting
`16#0000`	`Idle`	The function block is not active (basic state). `Ready = FALSE` `S_EquivalentOut =FALSE` `Error = FALSE`
`16#8001`	`Init`	The block has been activated. `Ready = TRUE` `S_EquivalentOut = FALSE` `Error = FALSE`
`16#8000`	`Safety Output Enabled`	The inputs are switched to `TRUE` in the equivalent mode `Ready = TRUE` `S_EquivalentOut = TRUE` `Error = FALSE`
`16#8004`	`Wait for Channel B`	Channel `A` has been switched to `TRUE`; wait for channel `B`; discrepancy timer started. `Ready = TRUE` `S_EquivalentOut = FALSE` `Error = FALSE`
`16#8014`	`Wait for Channel A`	Channel `B` has been switched to `TRUE`; wait for channel `A`; discrepancy timer started. `Ready = TRUE` `S_EquivalentOut = FALSE` `Error = FALSE`
`16#8005`	`From Active Wait`	One channel has been switched to `FALSE`; wait for the other channel to be switched to `FALSE`, discrepancy timer started. `Ready = TRUE` `S_EquivalentOut = FALSE` `Error = FALSE`