SF_Antivalent

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_Antivalent 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 antivalent SAFEBOOL inputs (NO/NC pair) 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 19. VAR_INPUT

Name	Data Type	Initial Value	Description, parameter values
`Activate`	`BOOL`	`FALSE`	See General Rules for Safety-Related Function Blocks
`S_ChannelNC`	`SAFEBOOL`	`FALSE`	Variable `NC` means `Normally Closed`. Input for `NC` connection `FALSE`: Contact `NC` open `TRUE`: Contact `NC` closed
`S_ChannelNO`	`SAFEBOOL`	`TRUE`	Variable `NO` means `Normally Open`. Input for `NO` connection `FALSE`: Contact `NO` open `TRUE`: Contact `NO` 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 20. VAR_OUTPUT

Name	Data Type	Initial Value	Description, parameter values
`Ready`	`BOOL`	`FALSE`	General output parameters
`S_AntivalentOut`	`SAFEBOOL`	`FALSE`	Safety-related output `FALSE`: At least one input signal is "not active" 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
`DiagCode`	`WORD`	`16#0000`	Diagnostic codes

Tip

"Antivalent" means that during normal operation, the two inputs are in opposite states at the same time. This is sometimes called "complementary" or "non-equivalent".

Figure 54. Function block: SF_Antivalent

Functional description

This function block processes two antivalent SAFEBOOL inputs to a SAFEBOOL output under discrepancy time monitoring. Both inputs are interdependent. The output of the function block shows the evaluation result of both channels.

If S_AntivalentOut = TRUE and one of the safety-oriented inputs changes, then the output immediately switches to FALSE.

Discrepancy time monitoring: The discrepancy time is the maximum time span in which both inputs may have the same state (this means that either both inputs are TRUE or both are FALSE) without the FB detecting an error. Discrepancy time monitoring starts when the status of an input changes. The function block detects an error when both inputs have the same values once the discrepancy time has elapsed.

The inputs must be switched symmetrically. This means that monitoring is performed both for switching the inputs to TRUE and FALSE.

Table 21. Logic table of inputs/outputs

Inputs				Outputs
`Activate`	`S_ChannelNC`	`S_ChannelNO`	`DiscrepancyTime`	`Ready`	`S_AntivalentOut`	`Error`	`DiagCode`
`FALSE`	`FALSE`	`TRUE`	Not started	`FALSE`	`FALSE`	`FALSE`	`16#0000`
`TRUE`	`FALSE`	`TRUE`	Not started	`TRUE`	`FALSE`	`FALSE`	`16#8001`
`TRUE`	`FALSE -> TRUE`	`TRUE`	Started	`TRUE`	`FALSE`	`FALSE`	`16#8004`
`TRUE`	`TRUE`	`TRUE -> FALSE`	Started	`TRUE`	`TRUE`	`FALSE`	`16#8000`
`TRUE`	`TRUE`	`FALSE`	Not started	`TRUE`	`TRUE`	`FALSE`	`16#8000`
`TRUE`	`TRUE`	`FALSE -> TRUE`	Started	`TRUE`	`FALSE`	`FALSE`	`16#800165`
`TRUE`	`TRUE -> FALSE`	`TRUE`	Started	`TRUE`	`FALSE`	`FALSE`	`16#8001`
`TRUE`	`FALSE`	`TRUE`	Not started	`TRUE`	`FALSE`	`FALSE`	`16#8001`
`TRUE`	`FALSE`	`TRUE -> FALSE`	Started	`TRUE`	`FALSE`	`FALSE`	`16#8014`
`TRUE`	`FALSE -> TRUE`	`FALSE`	Started	`TRUE`	`TRUE`	`FALSE`	`16#8000`
`TRUE`	`TRUE -> FALSE`	`FALSE`	Started	`TRUE`	`FALSE`	`FALSE`	`16#8005`
`TRUE`	`FALSE`	`FALSE -> TRUE`	Started	`TRUE`	`FALSE`	`FALSE`	`16#8001`

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 55. Status diagram: SF_Antivalent

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.

Typical timing diagrams

Figure 56. Time chart 1: SF_Antivalent.png

Figure 57. Time chart 2: SF_Antivalent.png

Error detection

The function block monitors the discrepancy time between Channel NO and Channel NC.

Error behavior

The S_AntivalentOut output is set to FALSE. Error is set to TRUE. DiagCode displays the error states. 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_AntivalentOut is present, Error is FALSE again.

FB-Specific Error and Status Codes

Table 22. FB-specific error codes

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

DiagCode

Statue Name

Status description and output setting

16#C001

Error 1

Discrepancy time expired in status 16#8004

Ready = TRUE

S_AntivalentOut = FALSE

Error = TRUE

16#C002

Error 2

Discrepancy time expired in status 16#8014

Ready = TRUE

S_AntivalentOut = FALSE

Error = TRUE

16#C003

Error 3

Discrepancy time expired in status 16#8005

Ready = TRUE

S_AntivalentOut = FALSE

Error = TRUE

Table 23. 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_AntivalentOut =FALSE` `Error = FALSE`
`16#8001`	`Init`	An activation has been detected by the block and the block is now activated. `Ready = TRUE` `S_AntivalentOut = FALSE` `Error = FALSE`
`16#8000`	`Safety Output Enabled`	The inputs are switched to active in the antivalent mode. `Ready = TRUE` `S_AntivalentOut = TRUE` `Error = FALSE`
`16#8004`	`Wait for NO`	`ChannelNC` has been switched to `TRUE`; wait until `ChannelNO` is switched to `FALSE`; discrepancy timer started. `Ready = TRUE` `S_AntivalentOut = FALSE` `Error = FALSE`
`16#8014`	`Wait for NC`	`ChannelNO` has been switched to `FALSE`; wait until `ChannelNC` is switched to `TRUE`; discrepancy timer started. `Ready = TRUE` `S_AntivalentOut = FALSE` `Error = FALSE`
`16#8005`	`From Active Wait`	One channel has been switched to inactive; wait for the second channel to be switched to inactive as well. `Ready = TRUE` `S_AntivalentOut = FALSE` `Error = FALSE`