OPC UA Safety supports Operator Acknowledgment both on the SafetyProvider side and on the SafetyConsumer side. For this purpose, both the interface of the SafetyProvider and the SafetyConsumer comprise a Boolean input called OperatorAckProvider and OperatorAckConsumer, respectively. The safety application can read the status of these inputs on the consumer side via the Boolean outputs OperatorAckRequested and OperatorAckProvider, respectively.

The following sections show some examples on how to use these inputs and outputs. Dashed lines indicate that the corresponding input or output are not used in this use case. For details, see Clause 7.3and Clause 7.4.

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Figure 28– OA in unidirectional safety communication

In this scenario, operator acknowledgment has to be done on the SafetyConsumer side, operator acknowledgment on the SafetyProvider side is not possible.

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Figure 29– Two-sided OA in bidirectional safety communication

In this scenario, operator acknowledgment is done independently for both directions.

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Figure 30– One sided OA in bidirectional safety communication

In this scenario (see Figure 30), an operator acknowledgment activated at controller A suffices for re-establishing the bidirectional connection. Both sides will cease delivering fail-safe values and continue sending process values. This is accomplished by connecting OperatorAckProvider with OperatorAckConsumer at the SafetyConsumer of controller B. Activating operator acknowledgment at controller B is not possible in this scenario.

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Figure 31– One sided OA on each side is possible

In this scenario (see Figure 31), an operator acknowledgment activated at controller A or controller B suffices for re-establishing the bidirectional connection. Both sides will cease delivering fail-safe values and continue sending process values. This is accomplished by the logic circuit shown in Figure 31.