Goal of this API

This specification defines what kind of interface the PLC has to provide via a OPC UA or KEB connection, so that HELIO can:

• Display all messages on a Message List page
• Display new incoming messages in dialogs
• Acknowledge incoming messages

Reference Implementation (OPC UA)

You can find a sample implementation of this specification using OPC UA in our Playground PLC:

→ The HELIO Playground PLC

This can also be utilized for creating HMIs with a spec-conformant PLC. The Playground PLC can later be replaced by the actual implementation.

<aside> <img src="/icons/light-bulb_gray.svg" alt="/icons/light-bulb_gray.svg" width="40px" /> Using OPC UA as a Reference Implementation

This guide will focus on implementing the Messaging API in OPC UA for clarity. However, other PLC Connection types, such as the KEB Connection (PLC Connection Type) , can also provide the messages using this specification.

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Message Types

HELIO uses three types of messages to provide guardrails on how to best communicate with operators.

• An Error occurs while the machine is running and requires human interaction to be resolved. Therefore, these errors typically need to be acknowledged by the operator to ensure that someone has actually provided a fix.
• A Warning is a message used to prevent errors from occurring in the first place. It provides operators with hints that certain thresholds have been exceeded and that it's time to act now in order to keep the machine running.
• All other messages fall into the category of Information. These messages can provide hints, tips on how to continue, or simply inform the user that a particular order has been completed. There are no limits to your imagination.

API Definition

The PLC must provide a way to:

• Query for messages and inform about new, incoming messages

  → MessageList (Folder)

• Acknowledge active messages

  → AcknowledgeMessage (Method)

Optional but helpful:

• A SimulateMessage method can be very useful to test your API.
• A HighestUnacknowledgedMessageLevel property can be very useful to test your API.
• A MessageCountUnacknowledged property to display how much message still have to be confirmed by operators.

Example implementation