7.4 SafetyConsumer interfaces

Figure 13 shows an overview of the SafetyConsumer interfaces. The Safety Application Program Interface (SAPI) is specified in Clause 7.4.1, the Safety Parameter Interface (SPI) is specified in Clause 7.4.3.

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Figure 13 – SafetyConsumer interfaces

7.4.1 SAPI of SafetyConsumer

The SAPI of the SafetyConsumer represents the safety communication layer services of the SafetyConsumer. Table 26 lists all inputs and outputs of the SAPI of the SafetyConsumer.

[RQ7.4] Each SafetyConsumer shall implement the SAPI as shown in Table 26, however, the details are vendor-specific.

Table 26 – SAPI of the SafetyConsumer

SAPI Term

Type

I/O

Definition

SafetyData

Structure

O

This output either delivers the process values received from the SafetyProvider in the SPDU field SafetyData, or FSV.

NonSafetyData

Structure

O

This output delivers the non-safety process values (e.g. diagnostic information) which were sent together with safe data, see Clause 8.2.1.10

Enable

Boolean

I

By changing this input to “0” the SafetyConsumer will change each and every variable of the SafetyData to “0”1 and stop sending requests to the SafetyProvider. When changing Enable to “1” the SafetyConsumer will restart safe communication. The variable can be used to delay the start of the OPC UA Safety communication, after power on until “OPC UA connection ready” is set. The delay time is not monitored while enable is set to “0”.

FSV_Activated

Boolean

O

This output indicates via “1”, that on the output SafetyData FSV (all binary “0”) are provided.

NOTE: If the ResponseSPDU is checked with error: ActivateFSV is set.

OperatorAckConsumer

Boolean

I

For motivation, see Clause 7.4.2.

After an indication of OperatorAckRequested this input can be used to signal an operator acknowledgment. By changing this input from “0” to “1” (rising edge) the SafetyConsumer is instructed to switch SafetyData from FSV to PV. OperatorAckConsumer is processed only if this rising edge arrives after OperatorAckRequested was set to “1”, see Figure 20.

If a rising edge of OperatorAckConsumer arrives before OperatorAckRequested becomes 1, this rising edge is ignored.

OperatorAckRequested

Boolean

O

This output indicates the request for operator acknowledgment. The bit is set to “1” by the SafetyConsumer, when three conditions are met:

  1. Too many communication errors were detected in the past, so the SafetyConsumer decided to switch to fail-safe substitute values.
  2. Currently, no communication errors occur, and hence operator acknowledgment is possible.
  3. Operator acknowledgment (rising edge at input OperatorAckConsumer) has not yet occurred.

The bit is reset to “0” when a rising edge at OperatorAckConsumer is detected.

OperatorAckProvider

Boolean

O

This output indicates that an operator acknowledgment has taken place on the SafetyProvider. If operator acknowledgment at the SafetyProvider should be allowed, this output is connected to OperatorAckConsumer, see Annex B.2.4 and B.2.5.

NOTE: If the ResponseSPDU is checked with error, this output remains at its last good value.

TestModeActivated

Boolean

O

The safety application program is expected to evaluate this output for determining whether the communication partner is in test mode or not. A value of “1” indicates that the communication partner (source of data) is in test mode, e.g., during commissioning. Data coming from a device in test mode may be used for testing but is not intended to be used to control safety-critical processes. A value of “0” represents the “normal” safety-related mode.

Motivation: Test mode enables the programmer and commissioner to validate the safety application using test data.NOTE: If the ResponseSPDU check results in an error and the SafetyErrorIntervalTimer (see Clause 7.4.3) is also not expired, TestModeActivated is reset.

SafetyProviderID

UInt32

I

For dynamic systems, this input can be set to a non-zero value. In this case, the SafetyConsumer uses this variable instead of the SPI-Parameter SafetyProviderIDConfigured. This input is only read in the first cycle, or when a rising edge occurs at the input Enable. See also Table 27. If it is changed to “0”, the value of SPI parameter SafetyProviderIDConfigured will be used (again).

For static systems, this input is usually always kept at value “0”.

SafetyBaseID

GUID

I

For dynamic systems, this input can be set to a non-zero value. In this case, the SafetyConsumer uses this variable instead of the SPI-Parameter SafetyBaseIDConfigured. This input is only read in the first cycle, or when a rising edge occurs at the input Enable. See also Table 27. If it is changed to “0”, the SPI-parameter SafetyBaseIDConfigured will become activated.

For static systems, this input is usually always kept at value “0”.

SafetyConsumerID

UInt32

I

For dynamic systems, this input can be set to a non-zero value. In this case, the SafetyConsumer uses this variable instead of the SPI-Parameter SafetyConsumerID. This input is only read in the first cycle, or when a rising edge occurs at the input Enable. See also Table 27. If it is changed to “0”, the SPI-parameter SafetyConsumerID will become activated.

For static systems, this input is usually always kept at value “0”.

7.4.2 Motivation for SAPI Operator Acknowledge (OperatorAckConsumer)

The safety argumentation assumes that random errors in the underlying OPC UA stack including its communication links are not too frequent, i.e., that its failure rate is lower than a given threshold, depending on the desired SIL (see Clause 11.3.1).

Whenever the SafetyConsumer detects a faulty message, it checks whether the assumption is still valid, and switches to fail-safe substitute values otherwise. Returning to process values then requires an operator acknowledgment.

Operator Acknowledge is expected to be initiated by a human operator who is responsible to check the installation, see Table 40, row “Operator Acknowledge”. For this reason, the parameter OperatorAckRequested is delivered by the SafetyConsumer to the safety application. See Clause B.2 for details on operator acknowledgment scenarios.

Timeout errors do only require an operator acknowledgment if operator acknowledgment is required by the safety function itself. In this case, SafetyOperatorAckNecessary is set to indicate that operator acknowledgments are required.

7.4.3 SPI of the SafetyConsumer

[RQ7.5] Each SafetyConsumer shall implement the parameters and constants [RQ7.5b] as shown in Table 27. The parameters (R/W in column “Access”) can be set via the SPI, whereas the constants (R in column “Access”) are read-only. The mechanisms for setting these parameters are vendor-specific. The attempt of setting a parameter to a value outside its range, or of the setting of a read-only parameter, shall not become effective, and a diagnostic message should be shown when appropriate. The SPI of the SafetyConsumer represents the parameters of the safety communication layer management of the SafetyConsumer. The values of the constants depend on the way the SafetyConsumer is implemented. They never change and are therefore not writable via any of the interfaces.

Table 27 – SPI of the SafetyConsumer

Identifier

Type

Valid range

Initial Value

(before configuration)

Access

Note

SafetyProviderIDConfigured

UInt32

0x0 - 0xFFFFFFFF

0x0

R/W

The SafetyProviderID of the SafetyProvider this SafetyConsumer normally connects to, see Figure 11 and Clause 3.2.

For dynamic systems, the safety application program can overwrite this ID by providing a non-zero value at the input SafetyProviderID of the safety Consumer’s SAPI. This runtime value can be queried using the SafetyProviderIDActive parameter. See note on configured and active values at Table 14.

SafetyBaseIDConfigured

GUID

any value which can be represented with sixteen bytes.

All sixteen bytes are 0x00

R/W

The default SafetyBaseID of the SafetyProvider this SafetyConsumer uses to make a connection, see Clause 3.2.

For dynamic systems, the safety application program can overwrite this ID by providing a non-zero value at the input SafetyBaseID of the SafetyConsumer’ s SAPI. This runtime value can be queried using the SafetyBaseIDActive parameter. See note on configured and active values at Table 14.

See Clause 11.1.1 for more information on GUID.

SafetyConsumerIDConfigured

UInt32

0x0 - 0xFFFFFFFF

0x0

R/W

ID of the SafetyConsumer, see Clause 11.1.2.

For dynamic systems, the safety application program can overwrite this ID by providing a non-zero value at the input SafetyConsumerID of the SafetyConsumer’s SAPI. This runtime value can be queried using the SafetyConsumerIDActive parameter. See note on configured and active values at Table 14.

SafetyProviderLevel

Byte

0x01 - 0x04

0x04

R/W

SafetyConsumer’s expectation on the SIL the SafetyProvider implementation (hardware & software) is capable of. See Clause 3.2, Clause 8.2.3.3, and Figure 12.

SafetyStructureSignature

UInt32

0x0 – 0xFFFFFFFF

0x0

R/W

Signature over the SafetyData structure, see Clause 8.2.3.4

SafetyStructureSignatureVersion

UInt16

0x1

0x1

R/W

Version used to calculate SafetyStructureSignature, see Clause 8.2.3.4

For the SafetyConsumer, this parameter is optional.

SafetyStructureIdentifier

String

“”

R/W

Identifier describing the data type of the safety data, see Clause 8.2.3.4.

For the SafetyConsumer, this parameter is optional.

SafetyConsumerTimeOut

UInt32

0x0 – 0xFFFFFFFF

0x0

R/W

Watchdog-time in microseconds (µs).

Whenever the SafetyConsumer sends a request to a SafetyProvider, its watchdog timer is set to this value. The expiration of this timer prior to receiving an error-free reply by the SafetyProvider indicates an unacceptable delay.

See Clause 10.1

SafetyOperatorAckNecessary

Boolean

0x0 / 0x1

0x1

R/W

This parameter controls whether an operator acknowledgment (OA) is necessary in case of errors of type “unacceptable delay” or “loss”, or when the SafetyProvider has activated FSV (ActivateFSV). 1: FSV are provided at the output SafetyData of the SAPI until OA. 0: PV are provided at SafetyData of the SAPI as soon as the communication is free of errors. In case of ActivateFSV the values change from FSV to PV as soon as ActivateFSV returns to “0”.

NOTE: This parameter does not have an influence on the behavior of the SafetyConsumer following the detection of other types of communication errors, such as data corruption or an error detected by the SPDU_ID. For these types of errors, OA is mandatory, see Clause 7.4.2.

SafetyErrorIntervalLimit

UInt16

6, 60, 600

600

R/W

Value in minutes.

The parameter SafetyErrorIntervalLimit determines the minimal time interval between two consecutive communication errors so that they do not trigger a switch to FSV in the SafetyConsumer, see Clause 7.4.2.

It affects the availability and the PFH/PFDavg of this OPC UA Safety communication link, see Clause 11.4.

SafetyClientImplemented

Boolean

0x0 / 0x1

n.a.

R

This read-only parameter indicates whether the SafetyConsumer has implemented the client part of OPC UA Client/Server communication (see Clause 4.3):

1: Client for OPC UA Client/Server communication is implemented.

0: Client for OPC UA Client/Server communication is not implemented.

SafetyPubSubImplemented

Boolean

0x0 / 0x1

n.a.

R

This read-only parameter indicates whether the SafetyConsumer has implemented the necessary publishers and subscribers for OPC UA PubSub communication (see Clause 4.3):

1: OPC UA PubSub communication is implemented.

0: OPC UA PubSub communication is not implemented.

7.4.4 Motivation for SPI SafetyOperatorAckNecessary

This parameter determines whether automatic restart (i.e., automatically switching back from fail-safe values to process values) is possible for the safety function or not. It is expected to be set to 1 for safety functions where automatic restart is not allowed and restart always requires human interaction.

If automatic restart of the safety function is safe, the parameter can be set to 0.