SF_GuardMonitoring

Help version 1.1 / Issue date: 2018.03
The following description is valid for the function block SF_GuardMonitoring_V2_0z, Version 2.0z (where z = 0 to 9).

Short Description The safety-related SF_GuardMonitoring function block monitors a guard (e.g., door) with two-stage interlocking according to the DIN EN ISO 14120 standard.
S_StartReset can be used to specify a start-up inhibit and S_AutoReset can be used to specify a restart inhibit.

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_GuardSwitch1 and S_GuardSwitch2

Short description Value

State-controlled inputs for the connected position switches of the door.
For the S_GuardMonitoring output to switch to SAFETRUE, both inputs S_GuardSwitch1 and S_GuardSwitch2 must switch to SAFETRUE within the time set at DiscrepancyTime.
Data type: SAFEBOOL
Initial value: SAFEFALSE

Note
If only one signal reports the status of the door (one position switch only), this must be connected in parallel to both inputs S_GuardSwitch1 and S_GuardSwitch2. Where this is the case, a time of 0 seconds must be set at DiscrepancyTime.

SAFEFALSE: Position switch reports open state

SAFETRUE: Position switch reports closed state

Refer to the topic "S_GuardSwitch1 and S_GuardSwitch2" for details.

DiscrepancyTime

Short description Value

Input for specifying the maximum permissible discrepancy time for the closing operation of the safety equipment.
Data type: TIME
Initial value: #0ms
If S_GuardSwitch1 or S_GuardSwitch2 switches to SAFETRUE, the respective other input (S_GuardSwitch1 or S_GuardSwitch2) must also switch to SAFETRUE within the time set at DiscrepancyTime for the switching operation to be considered as valid.
If not both inputs have switched to SAFETRUE after the time set at DiscrepancyTime has elapsed, an error message is generated (Error = TRUE) and the S_GuardMonitoring output remains in the defined safe state SAFEFALSE. Enter a time value according to your risk analysis.

WARNING

Non-conformance to safety function requirements

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

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

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

Refer to the topic "DiscrepancyTime" for details.

S_StartReset

Short description Value

State-controlled input for specifying the start-up inhibit after the Safety PLC has been started up or the function block has been activated.
An active start-up inhibit must be removed manually by means of a positive signal edge at the Reset input. A deactivated start-up inhibit causes the S_GuardMonitoring output to switch to SAFETRUE automatically when the function block is activated and the safety-related function is not requested.
Data type: SAFEBOOL
Initial value: SAFEFALSE

SAFEFALSE: With start-up inhibit

SAFETRUE: Without start-up inhibit

WARNING

Non-conformance to safety function requirements

Verify the impact of a deactivated start-up inhibit (S_StartReset = SAFETRUE) and/or restart inhibit (S_AutoReset = SAFETRUE) on your machine or process prior to implementation.

Observe the regulations given by relevant sector standards regarding the start-up/restart inhibit.

Verify that a suitable start-up inhibit is in place at another location or using other means.

Refer to the topic "S_StartReset" for details.

S_AutoReset

Short description Value

State-controlled input for specifying the restart inhibit after the previously opened safety equipment has been closed (in other words, after the SAFETRUE signal has returned at inputs S_GuardSwitch1 and S_GuardSwitch2).
Data type: SAFEBOOL
Initial value: SAFEFALSE
An active restart inhibit must be removed manually by a positive signal edge at the Reset input. A deactivated restart inhibit causes the S_GuardMonitoring output to switch to SAFETRUE automatically when the function block is activated and the safety-related function is no longer requested.

SAFEFALSE: With restart inhibit

SAFETRUE: Without restart inhibit

WARNING

Non-conformance to safety function requirements

Verify the impact of a deactivated start-up inhibit (S_StartReset = SAFETRUE) and/or restart inhibit (S_AutoReset = SAFETRUE) on your machine or process prior to implementation.

Observe the regulations given by relevant sector standards regarding the start-up/restart inhibit.

Verify that a suitable start-up inhibit is in place at another location or using other means.

Refer to the topic "S_AutoReset" 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.

Manual resetting of an active start-up/restart inhibit (depending on which type(s) of inhibit the function block provides).

Data type: BOOL
Initial value: FALSE

FALSE: Reset is not requested

Edge FALSE > TRUE: Reset is requested

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 function block SF_Reset.

Resetting the function block by means of a positive signal edge at the Reset input can cause the S_GuardMonitoring output to switch to SAFETRUE immediately (depending on the status of the other inputs).

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_GuardMonitoring

Short description Value

Output for enable signal of the function block.
Data type: SAFEBOOL

SAFEFALSE:

The guard is not closed (S_GuardSwitch1 and/or S_GuardSwitch2 = SAFEFALSE)

or the function block is not activated

or the start-up/restart inhibit is active

or an error message is present.

SAFETRUE:

Guard closed (S_GuardSwitch1 and S_GuardSwitch2 = SAFETRUE)

and the function block is activated

and the start-up/restart inhibit is not active

and no error message is present.

Refer to the topic "S_GuardMonitoring" 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_GuardMonitoring 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

This diagram is based on typical monitoring of a guard with two-stage interlocking, where both position switches connected to inputs S_GuardSwitch1 and S_GuardSwitch2 switch within the time set at DiscrepancyTime.
Additional assumptions:

S_StartReset = SAFEFALSE: Start-up inhibit after the function block has been activated and the Safety PLC has started up

S_AutoReset = SAFEFALSE: Restart inhibit after the previously opened safety equipment has been closed (i.e., after the SAFETRUE signals have returned at inputs S_GuardSwitch1 and S_GuardSwitch2).

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 Both inputs S_GuardSwitch1 and S_GuardSwitch2 are SAFETRUE. However, the S_GuardMonitoring output is still SAFEFALSE, since a start-up inhibit is specified after the Safety PLC has been started up by S_StartReset = SAFEFALSE.

2 A positive edge at the Reset input resets the start-up inhibit and the S_GuardMonitoring output switches to SAFETRUE.

3 The safety equipment is opened. S_GuardSwitch2 and S_GuardSwitch1 switch to SAFEFALSE one after the other, and the S_GuardMonitoring output becomes SAFEFALSE.

4 The safety equipment is closed. Measurement of the discrepancy time begins with the switch from SAFEFALSE to SAFETRUE at S_GuardSwitch2. The second input S_GuardSwitch1 also switches to SAFETRUE during the time set at DiscrepancyTime.
As a restart inhibit is specified by S_AutoReset = SAFEFALSE after the safety equipment has been closed (S_GuardSwitch1 and S_GuardSwitch2 = SAFETRUE), the S_GuardMonitoring output only becomes SAFETRUE once the restart inhibit has been removed by a positive edge at the Reset input.

5 The safety equipment is opened. S_GuardSwitch1 and S_GuardSwitch2 switch to SAFEFALSE one after the other, and the S_GuardMonitoring output becomes SAFEFALSE.

6 The safety equipment is closed. Both inputs S_GuardSwitch1 and S_GuardSwitch2 become SAFETRUE at the same time. The function block detects the permanent TRUE signal at the Reset input as an error. Output Error becomes TRUE and output S_GuardMonitoring remains SAFEFALSE.

7 The Reset input becomes FALSE; this causes the error message to be reset.

Application example: Door monitoring using a mechanical position switch, start-up inhibits activated

This example describes how a mechanically activated position switch with 2 N/C contacts is evaluated using the safety-related SF_GuardMonitoring function block. Position switch B1 is connected to input terminals 1.1 and 2.1 of safety-related input device PSDI 1.

The signals from position switch B1 are evaluated, based on two channels, for equivalence in the safety-related input device, which has been parameterized accordingly. The resulting signal is assigned to the global I/O variable B1_GMControl_In. This variable is connected to the inputs S_GuardSwitch1 and S_GuardSwitch2 of the safety-related SF_GuardMonitoring function block for evaluation.
B1_GMControl_In is SAFETRUE if both inputs of the safety-related input device PSDI 1 are SAFETRUE at the same time (safety equipment closed) and the safety-related input device PSDI 1 does not report any errors as regards exceeding the time set at DiscrepancyTime.

Note
Since only one signal reports the status of the door in this example (one position switch), this is connected in parallel to both inputs S_GuardSwitch1 and S_GuardSwitch2. In this case, a value of 0 seconds is set at input DiscrepancyTime.

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

S_StartReset = SAFEFALSE specifies a start-up inhibit after the Safety PLC has been started up or the function block has been activated. Furthermore, S_AutoReset = SAFEFALSE specifies a restart inhibit for the function block after the door has been closed. Both inhibits are only removed when there is a positive signal edge at the Reset input.
To this end, the S1 reset button is connected to input terminal 1.1 of the standard input device DI 1. The terminal is assigned to the global I/O variable S1_Reset_GM, which in turn is connected to the function block input Reset.

Note
The enable signal at the S_GuardMonitoring output of the SF_GuardMonitoring function block is connected to additional safety-related function blocks or functions and controls the application accordingly.

S1 Reset

B1 Door switch with two positively driven N/C contacts for positive opening operation (SAFETRUE, if safety equipment closed).

(*1) Door: open

(*2) Door: closed

See note above the illustration.

Further Info
The other application examples 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 FBs (user-defined POUs as well as library FBs, such as IEC standard FBs, firmware FBs, 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 the 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 user-defined function block

The user-defined function block 'TLC' ("Two Level Controller") is added to the 'Functions & Function Blocks' category (COMPONENTS area). It shall be called twice in the program POU 'Container' to control the filling level and the temperature of a boiler.

For both FB instances, an instance name declaration is added to the 'Variables' table of the calling program POU 'Container': TLCTemperature and TLCLevel. Thus the 'TLC' function block can be called twice in the code worksheet of the calling POU by means of these instance names.
Both FB instances have been inserted into the 'Container' code worksheet, each instance with different variables connected to its input and output formal parameters ('Level...' and 'Temperature...').

Additional information is available in the following sections:

Functional description

Additional signal sequence diagrams

Additional application examples

Fault avoidance

Implementation of safety requirements from applicable standards