SF_GuardMonitoring

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_GuardMonitoring 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 FB monitors the relevant safety guard with a two-stage interlock. It is used to support the "guard without interlocking" function (guard door monitoring) in an application. There are two independent input parameters for two switches of the safety guard. These two independent input parameters are coupled with the time difference (MonitoringTime) to close the guard.

Table 33. VAR_INPUT

Name	Data Type	Initial Value	Description, parameter values
`Activate`	`BOOL`	`FALSE`	General input parameters
`S_GuardSwitch1`	`SAFEBOOL`	`FALSE`	Variable. Guard switch 1 input. `FALSE`: Guard open `TRUE`: Guard closed.
`S_GuardSwitch2`	`SAFEBOOL`	`FALSE`	Variable. Guard switch 2 input. `FALSE`: Guard open `TRUE`: Guard closed.
`DiscrepancyTime`	`TIME`	`T#0ms`	Constant. Sets the monitored synchronous time between `S_GuardSwitch1` and `S_GuradSwitch2`. The `DiscrepancyTime` caution note must be observed.
`S_StartReset`	`SAFEBOOL`	`FALSE`	General input parameters
`S_AutoReset`	`SAFEBOOL`	`FALSE`	General input parameters
`Reset`	`BOOL`	`FALSE`	General input parameters

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 34. VAR_OUTPUT

Name	Data Type	Initial Value	Description, parameter values
`Ready`	`BOOL`	`FALSE`	General output parameters
`S_GuardMonitoring`	`SAFEBOOL`	`FALSE`	Output, for status indication of the guard. `FALSE`: The guard is not active. `TRUE`: `S_GuardSwitch1` and `S_GuardSwitch2` are `TRUE` and no error, and confirmation. The guard is active.
`Error`	`BOOL`	`FALSE`	General output parameters
`DiagCode`	`WORD`	`16#0000`	Diagnostic codes

Figure 69. Function block: SF_GuardMonitoring

Functional description: SF_GuardMonitoring

This function block requires two inputs which map the position of the safety guard with two switches: a discrepancy time input and a Reset input. If the safety guard has only one switch, then the S_GuardSwitch1 and S_GuardSwitch2 inputs can be bridged. The watchdog time is the maximum time within which the two switches must be closed for the safety guard to close. The Reset, S_StartReset and S_AutoReset inputs define how the function block is reset after the safety guard has been opened.

When the safety guard is opened, the two inputs S_GuardSwitch1 and S_GuardSwitch2 should switch to FALSE. The S_GuardMonitoring output switches to FALSE as soon as one of the two inputs S_GuardSwitch1 or S_GuardSwitch2 is set to FALSE. To close the safety guard, both inputs S_GuardSwitch1 and S_GuardSwitch2 have to switch to TRUE.

SF_GuardMonitoring monitors the symmetry of the switching process. The S_GuardMonitoring output remains FALSE if only one of the contacts has completed the open/close process.

The behavior of the S_GuardMonitoring output depends on the time difference of both switching inputs. The discrepancy time is monitored as soon as the value of the two inputs S_GuardSwitch1/S_GuardSwitch2 differs. If the discrepancy time has been exceeded but both inputs still differ, then the S_GuardMonitoring output remains FALSE. If the second respective S_GuardSwitch1/S_GuardSwitch2 input switches to TRUE within the discrepancy time, then the S_GuardMonitoring output is set to TRUE, with subsequent confirmation.

Caution

The S_StartReset and S_AutoReset inputs shall only be activated if it is ensured that no hazardous situation can arise when the S-PLC is started.

Status diagram

Figure 70. Status diagram: SF_GuardMonitoring

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 71. Timing diagram 1: GuardMonitoring

Figure 72. Timing diagram 2: SF_GuardMonitoring

Error detection

External signals: SAFEBOOL inputs provide their own error detection. Mechanical setup combines that of an open and closed switch according to the EN 954 standard. Discrepancy time monitoring for the time delay between both mechanical switch reactions, according to the EN 954 standard.

An error is detected when the time delay between the first and the second S_GuardSwitch1/S_GuardSwitch2 input is greater than the value of the DiscrepancyTime input. The error output is set to TRUE.

The POU detects a static TRUE signal at the Reset input.

Error and reset behavior

The S_GuardMonitoring output is set to FALSE. If the two inputs S_GuardSwitch1 and S_GuardSwitch2 are bridged, then no error is detected. To exit the reset state, the Reset input has to be set to FALSE. To exit the discrepancy time error, both inputs S_GuardSwitch1 and S_GuardSwitch2 have to be set to FALSE.

FB-Specific Error and Status Codes

Table 35. FB-specific error codes

`DiagCode`	Statue Name	Status description and output setting
`16#C001`	`Reset Error`	Static reset detected in state `8003`. `Ready = TRUE` `S_GuardMonitoring = FALSE` `Error = TRUE`
`16#C011`	`Discrepancytime Error 1`	Discrepancy time expired in state `8004` `Ready = TRUE` `S_GuardMonitoring = FALSE` `Error = TRUE`
`16#C012`	`Discrepancytime Error 1`	Discrepancy time expired in state `8014` `Ready = TRUE` `S_GuardMonitoring = FALSE` `Error = TRUE`

DiagCode

Statue Name

Status description and output setting

16#C001

Reset Error

Static reset detected in state 8003.

Ready = TRUE

S_GuardMonitoring = FALSE

Error = TRUE

16#C011

Discrepancytime Error 1

Discrepancy time expired in state 8004

Ready = TRUE

S_GuardMonitoring = FALSE

Error = TRUE

16#C012

Discrepancytime Error 1

Discrepancy time expired in state 8014

Ready = TRUE

S_GuardMonitoring = FALSE

Error = TRUE

Table 36. FB-specific status codes (no error)

`DiagCode`	Statue Name	Status description and output setting
`16#0000`	`Idle`	The function block is not active (basic state). `Ready = FALSE` `S_GuardMonitoring = FALSE` `Error = FALSE`
`16#8000`	`Normal`	Safety guard closed and safety status confirmed. `Ready = TRUE` `S_GuardMonitoring = TRUE` `Error = FALSE`
`16#8001`	`Init`	The block has been activated. `Ready = TRUE` `S_GuardMonitoring = FALSE` `Error = FALSE`
`16#8002`	`Open Guard Request`	Complete switching sequence required. `Ready = TRUE` `S_GuardMonitoring = FALSE` `Error = FALSE`
`16#8003`	`Wait for Reset`	Wait for rising trigger edge to Reset. `Ready = TRUE` `S_GuardMonitoring = FALSE` `Error = FALSE`
`16#8012`	`Guard opened`	The guard is completely open. `Ready = TRUE` `S_GuardMonitoring = FALSE` `Error = FALSE`
`16#8004`	`Wait for GuardSwitch 2`	`S_GuardSwitch1` was switched to `TRUE`; wait for `S_GuardSwitch2`; discrepancy timer started. `Ready = TRUE` `S_GuardMonitoring = FALSE` `Error = FALSE`
`16#8014`	`Wait for GuardSwitch 1`	`S_GuardSwitch2` was switched to `TRUE`; wait for `S_GuardSwitch2`; discrepancy timer started. `Ready = TRUE` `S_GuardMonitoring = FALSE` `Error = FALSE`
`16#8005`	`Guard Closed`	The guard is closed. Wait for `Reset` if `S_AutoReset = FALSE`. `Ready = TRUE` `S_GuardMonitoring = FALSE` `Error = FALSE`