UA Part 15: Safety - 7.4 SafetyConsumer interfaces

7.4 SafetyConsumer interfaces

The Figure 12 shows an overview of the SafetyConsumer interfaces. The SAPI is specified in Clause 7.4.1, the SPI is specified in Clause 7.4.3.

Figure 12 – SafetyConsumer interfaces

7.4.1 SAPI of SafetyConsumer

The SAPI of the SafetyConsumer represents the Safety communication layer services of the SafetyConsumer. Table 16 lists all inputs and outputs of the SAPI of the SafetyConsumer. [RQ7.4] Each SafetyConsumer shall implement the SAPI as shown in Table 16, however, the details are vendor specific.

Table 16 – SAPI of the SafetyConsumer

SAPI Term	Type	Definition
*SafetyData*	Structure	This output either delivers the process values received from the SafetyProvider in the SPDU field SafetyData, or FSV.
*NonSafetyData*	Structure	Used to consistently transmit non-safety data values (e.g. diagnostic information) together with safe data, see Clause 8.1.1.10
*Enable*	Boolean	By changing this input to "0" the SafetyConsumer will change each and every variable of the SafetyData to "0" 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	This output indicates via "1", that on the output SafetyData FSV (all binary "0") are provided. NOTE: If an application needs different FSV than “all binary 0”, it is expected to use appropriate constants and ignore the output of SafetyData whenever FSV_Activated is set. NOTE: If the ResponseSPDU is checked with error: ActivateFSV is set.
OperatorAckConsumer	Boolean	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 18. If a rising edge of OperatorAckConsumer arrives before OperatorAckRequested becomes 1, this rising edge is ignored.
OperatorAckRequested	Boolean	This output indicates the request for operator acknowledgment. The bit is set to “1” by the SafetyConsumer, when three conditions are met: Too many communication errors were detected in the past, so the SafetyConsumer decided to switch to fail-safe substitute values. Currently, no communication errors occur, and hence operator acknowledgment is possible. 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	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 last value.
*TestModeActivated*	Boolean	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 is checked with error: TestModeActivated is reset.
*SafetyProviderID*	UInt32	By changing this input to a non-zero value, the SafetyConsumer uses this variable instead of the SPI-Parameter SafetyProviderID. This input is only read in the first cycle, or when a rising edge occurs at the input Enable. See also Table 17. If it is changed to “0”, the parameter SafetyProviderID will become activated.
*SafetyBaseID*	GUID	By changing this input to a non-zero-value the SafetyConsumer uses this variable instead of the SPI-Parameter SafetyBaseID. This input is only read in the first cycle, or when a rising edge occurs at the input Enable. See also Table 17. If it is changed to “0”, the SPI-parameter SafetyBaseID will become activated.
*SafetyConsumerID*	UInt32	By changing this input to a non-zero-value 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 17. If it is changed to “0”, the SPI-parameter SafetyConsumerID will become activated.

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.

Whenever the SafetyConsumer detects a faulty telegram, 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 32, row Operator Acknowledge”. For this reason, the OperatorAckConsumer is delivered to the safety application program to deal with.

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 required.

7.4.3 SPI of the SafetyConsumer

[RQ7.5] Each SafetyConsumer shall implement the parameters shown in Table 17 which can be set via the SPI. The mechanisms for setting these parameters are vendor specific. The SPI of the SafetyConsumer represents the parameters of the Safety communication layer management of the SafetyConsumer.

Table 17 – SPI of the SafetyConsumer

Identifier	Type	Valid range	Initial Value (before parametrization)	Note
SafetyBaseID	GUID	See Clause 11.1.1	0x0	The default SafetyBaseID of the SafetyProvider this SafetyConsumer uses to make a connection, see Clause 3.2.25. 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.
SafetyProviderID	UInt32	0x1 - 0xFFFFFFFF	0x0	The SafetyProviderID of the SafetyProvider this SafetyConsumer normally connects to, see Figure 10 and Clause 3.2.26. 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.
SafetyConsumerID	UInt32	0x1 - 0xFFFFFFFF	0x0	ID of the SafetyConsumer, see Clause 11.1.2.
SafetyStructureSignature	UInt32	0x1 – 0xFFFFFFFF	0x0	Signature over the SafetyData structure, see Clause 8.1.3.4
SafetyConsumerTimeOut	UInt32	0x1 – 0xFFFFFFFF	0x1	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 10.2
SafetyOperatorAckNecessary	Boolean	0x0 / 0x1Default 1	0x1	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. For these types of errors, OA is mandatory, see Clause 7.4.2.
SafetyErrorIntervalLimit	UInt16	6, 60, 600	600	Value in minutes. The parameter SafetyErrorIntervalLimit determines the minimum distance two consecutive communication errors must have for not triggering a switch to FSV in the SafetyConsumer. It affects the availability and the PFH of this OPC UA Safety link, see Clause 7.4.2 and Clause 11.4.
SafetyProviderLevel	Byte	0x01 - 0x04	0x1	SafetyConsumer’s expectation on the maximal SIL the SafetyProvider implementation (hardware & software) is capable of. See Clause 7.3.3, Clause 8.1.3.3, and Figure 11.

NOTE: the engineering system can use the initial value to set a parameter to a safe value.

7.4.4 Motivation for SPI SafetyOperatorAckNecessary

This parameter determines whether automatic restart 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.