Connect OPC UA to Ignition (Inductive Automation)

Before you start

• A licensed Ignition gateway with the OPC UA and driver modules you intend to use. Which modules are included in your licence, and how tags are counted, must be confirmed with Inductive Automation.
• Network reachability from the gateway to each PLC endpoint, or a reverse-connect arrangement where the network layer only permits outbound sessions.
• Gateway web-interface access with configuration rights, because certificate approval and OPC connections both live there.
• A decision about whether downstream systems consume Ignition's own OPC UA server or its historian and MQTT paths instead, since that decides where your tag semantics live.

Setting it up

1. Add the remote server as an OPC client connectionIn the gateway configuration, add an OPC UA client connection with the endpoint URL, the security policy and mode the server offers, and the identity token it accepts. Start with security None to prove the network path, then move to a signed and encrypted endpoint as a separate change so you know which change broke what.
2. Approve the certificates in both directionsThe first secure attempt normally leaves the connection faulted. The gateway quarantines the server certificate it did not trust; approve it in the gateway's certificate configuration. Then move the gateway's own client certificate from the PLC's rejected store into its trusted store. Neither side works alone.
3. Browse the server from the OPC browser and confirm the modelUse the gateway's OPC browser to walk the address space and check type definitions on the nodes you care about. This tells you in a minute whether the machine is modelled to a companion specification or is a flat tag dump, which decides how much mapping work follows.
4. Create tags by dragging from the browser, not by typing pathsDragging nodes into a tag folder builds the OPC item path for you and avoids transcription errors. Keep the tag hierarchy aligned to plant structure rather than to PLC data-block structure, because the tag tree is what every downstream consumer sees.
5. Replace raw namespace indexes in item paths where you canIgnition tag item paths carry the namespace index as written. If the PLC renumbers namespaces after a program download, every affected tag goes bad at once. Keep the mapping in one place, document which index belongs to which namespace URI, and re-verify after any PLC download.
6. Configure Ignition's own OPC UA server deliberatelyThe gateway serves its tags over OPC UA on its own endpoint, by default port 62541. Decide whether that endpoint should exist at all, which security policies it offers and who may connect, then complete the trust exchange with each consumer.
7. Set scan classes to the cadence the data needsTag groups drive the subscription rates Ignition requests from the PLC. Fewer distinct rates means fewer subscriptions on an embedded server, which is often the difference between a stable and an unstable PLC connection.

What the address space looks like

Two address spaces are in play and confusing them causes most Ignition integration arguments. Southbound, Ignition sees whatever the PLC or gateway publishes, with its namespace indexes and its identifiers, and stores that as an OPC item path per tag. Northbound, Ignition publishes its own tag tree through its OPC UA server, so consumers see Ignition's folder structure and tag names, not the PLC's. That republished tree is a flat-ish tag hierarchy with Ignition's own naming, not a companion-specification model: it carries no machine identity types, no standard state machines and no standard counters unless you built equivalents as tags. If you need portable semantics downstream, the modelling decision is the shape of the Ignition tag tree.

The traps

• The first secure connection failing is normal, and the failure is symmetrical. Certificate approval is the biggest single deployment hurdle across the whole gateway estate, so establish a documented procedure before the tenth machine rather than after it.
• Tag item paths hold the namespace index literally. A PLC program download that shifts indexes turns a whole folder of tags bad at once, and the symptom on the PLC side is BadNodeIdUnknown against nodes that still exist.
• Ignition's own OPC UA server is a real, exposed server. If it is left with permissive security because it is internal, it is an unauthenticated route to every tag in the plant.
• Every distinct tag group rate becomes a separate subscription on the PLC. Embedded servers have low subscription ceilings, so proliferating tag groups is a common cause of intermittent PLC connection faults.
• Ignition holds a last known value with a quality attached. A dashboard reading a stale value looks identical to one reading a live value unless the quality is displayed, so put quality on the screens that matter and handle bad quality explicitly in any calculation.
• The historian records what Ignition subscribed to at the rate it subscribed. Widening a tag group later does not retroactively improve resolution, and OEE calculations built on the old resolution will silently change behaviour.

Getting OEE data out of it

Ignition is a reasonable place to compute OEE and a poor place to invent the data for it. Availability needs a machine state signal, not an inferred running bit: subscribe to a state variable and store transitions, because a tag group sampling once a second cannot see a 400 ms stop. Counts should come from PLC counters read as values, with rollover and reset handled in the transform, not from Ignition counting edges. Reasons are best carried as alarms or as a documented reason code, so downtime can be attributed rather than guessed. Ignition can hold shift calendars, planned production time and standard cycle times as its own data, which is genuinely useful, but be clear that this is data you entered, not data from the machine, and that it must reconcile with whatever MES or ERP considers authoritative.

Last verified 7 September 2026 against OPC UA 1.05.07. OPC UA Connect is an educational resource and is not affiliated with the OPC Foundation.