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OPC UA Equipment Monitor

A stale reading must never look live

  • Completed
  • May 2023
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An operator is watching a machine on a dashboard and the connection drops. The question that matters is whether the screen carries on showing the last numbers as though they were live.

A .NET 8 service subscribes to node changes on an OPC UA server and streams them over SignalR to an Angular dashboard that charts them as they arrive.

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Evidence

What it looks like running

  • Data-change notifications arriving on the subscription, then the OPC session dropping and the header showing the attempt, the server's own error and the countdown to the next retry
  • Six monitored items on one subscription, each card carrying its value, source timestamp, age, status code and configured band
  • Address space browsed one level at a time with each level's variables read as it is fetched, and a variable subscribed from the tree appearing as a new card
  • The OPC session dropped: the attempt number, elapsed time, the server's own error and the backoff countdown are all on screen while the last received values stay up
  • The browser's own socket to the service dropped, a different failure from the OPC session: the session field is marked last known and the held values are labelled as held
  • The same build against a public demo server, browsing that server's address space and flagging a node whose subscription has reported nothing as quiet rather than broken

Engineering

How it was built

Frontend

  • Angular dashboard charting values as they arrive
  • Last-known values held and labelled on link loss, with the age since the last update
  • Address-space tree for choosing which nodes to monitor

Backend & services

  • .NET 8 OPC UA client, nodes resolved by browse path or node id
  • Subscriptions with per-node quality, timestamp and value band
  • SignalR hub streaming updates to every connected dashboard
  • Equipment session state tracked and published separately from the dashboard socket

Testing & verification

  • 81 tests
  • Verified against a live public OPC UA server: session, browse paths and subscriptions

Applied

Skills on this project

.NETC#OPC UASCADASignalRAngularReal-time systems

Next step

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