OPC UA

The OPC UA configuration pages define OPC UA devices and OPC UA variables. Use the device page to configure the endpoint and security-related connection information. Use the variable page to map individual nodes into the EnvisionSCADA variable namespace.

OPC UA is suitable when structured node browsing and standardized industrial communication are required. Plan naming carefully so node paths remain understandable after import or manual configuration.

Keep security certificates and endpoint behavior consistent with the target server requirements, especially when moving between development and production environments.

Device Settings

Each OPC UA device defines a client connection to an OPC UA server. Configure the connection endpoint, user authentication, secure channel behavior, and subscription timing.

Create a new device with the Add button in the toolbar. The Add device dialog contains all device settings organized in the tabs General, Connection, and Subscription, with default values already filled in. Enter at least the Name and Server URL and press Create.

The device row shows Enable, Name, Server URL, Template, and Description directly and these values can be edited in place. Press the Settings icon on a device row to open the Edit device dialog, which contains the same tabs and all settings of the device. Press Save to apply the changes.

Subscriptions

Each OPC UA device supports up to 5 subscriptions. Subscriptions group monitored items that share the same publishing interval and lifetime behavior. Variables are assigned to a subscription using their Subscription field.

Variable Settings

Each OPC UA variable maps a server node to a named variable in the EnvisionSCADA namespace.

Create a new variable with the Add button in the toolbar. The Add variable dialog organizes all variable settings in the tabs General, Scaling, Historian, and Gateway, with default values already filled in. Enter at least the Name and Node ID on the General tab and press Create. When the variable is created on a template device, it is also created on all instance devices that use the template. On a template device, start the Name with the {Device} replacer, so that each instance device gets its own variable. The Name must resolve to a different variable on each device; this is checked for every instance device before anything is saved, when a variable is created and when it is renamed. The Browse button in the toolbar shows the server address space as a tree and creates variables directly from it, as described in Browsing the Address Space.

The variable row shows Enable, Name, Asset, Data Type, Node ID, Sampling Interval, Subscription, and Description directly and these values can be edited in place. Press the Settings icon on a variable row to open the Edit variable dialog, which contains the same tabs and all settings of the variable. Press Save to apply the changes. Changes made on a template device are also applied to the matching variable on all instance devices, while each instance keeps its own Modbus Address value. The Gateway tab settings Modbus Address, OPC UA, Writeable, MQTT Publisher, Kafka Device, Kafka Remap Device, and Kafka Remap Variable are also available as table columns, which are shown with Columns as described in the Configuration Tables article.

Browsing the Address Space

The Browse button in the toolbar opens the Browse dialog, which shows the server address space as a tree. The dialog opens on the top level of the server and reads each branch only when it is opened, so the dialog is available immediately regardless of the size of the address space.

Press a branch to open it and read the nodes below it. Nodes that hold a value show their Node ID, Data Type, live Value, Units, Min and Max in the columns next to the name. For nodes of type AnalogItemType, the Units, Min and Max columns are filled from the EngineeringUnits and EURange properties of the node on the server.

Tick the checkbox of a node to select it. Ticking the checkbox of a branch reads the whole branch and selects every variable below it, which is the fastest way to take over a complete device. A branch whose variables are partly selected shows a partially ticked checkbox. The footer shows how many of the variables read so far are selected.

Expand All reads and opens the complete address space at once. On a large server this takes the time of a full browse, so open the branches you need instead when the server is large.

Enter text in the search field to list every variable read so far whose name or Node ID contains the text, as a flat list without the tree. Clear the search field to return to the tree. Searching does not change the selection.

Add Selected creates a variable for every selected node, using the browsed name, Node ID, Data Type, Units, Min Raw and Max Raw. With Start names with {Device}. selected, which is the default, each variable name starts with the {Device} replacer, so the same node added on several devices, or on a template device and its instance devices, gives each device its own variable. Clear Start names with {Device}. to use the browsed name as it is. A plain name must be unique across the whole project, and a template device with instance devices requires the {Device} replacer. Nodes that already exist as a variable on the device, with or without the {Device}. prefix, are reported and skipped. When one of the selected nodes cannot be added, the message names its Node ID and no variable is created.

Update Node IDs writes the Node ID of every selected node onto the existing variable of the same name, with or without the {Device}. prefix, which re-points variables after the server address space has changed. Selected nodes without a matching variable on the device are listed in the result message. Both buttons become available once at least one node is selected.

The browsed name is taken from the server. A node with a string Node ID uses the identifier of that Node ID, which carries the path the server itself uses, and a node with a numeric Node ID uses its browse name. Dots are kept, so with Start names with {Device}. selected a node with Node ID ns=2;s=Channel1.Device1.Tag1 is added as the variable {Device}.Channel1.Device1.Tag1 and is referenced as PLC1.Channel1.Device1.Tag1 on a device named PLC1. A dot is only valid between two parts of a name, so a dot at the start or the end of a browsed name is written as an underscore and repeated dots are reduced to one.

Characters that a variable name does not accept are converted. The characters \ / : ; and the double quote are removed, and every other character except letters, digits, underscores, dots and square brackets, such as a space, a dash or #, is written as an underscore.

Variables added by an earlier version keep the name they were created with, for example a name where dots and dashes were written as underscores. Add Selected and Update Node IDs match these variables as well, so adding such a node again skips the existing variable and re-pointing an existing device keeps working after an upgrade.

Supported Data Types

The Data Type field determines how the OPC UA value is interpreted.

Node ID Format

The Node ID field uses the standard OPC UA node identifier format. The namespace index and identifier type are separated by semicolons.

Variable Arrays

An OPC UA variable can expand into an array by setting the Array size field to a value between 2 and 512. The variable itself is the first element and its Name must end in the first index, for example Sim_OPCUA.Temps[0]. All elements share the same Node id: the node is array-valued on the server, the subscription is created once, and the received array is distributed to the elements by position. Writing an element writes only that position of the array on the server.

The element rows are managed by the first element and appear locked in the variable list. Changing the Array size adds or removes elements at the end; renaming the first element renames all elements. The Training Simulator serves the array node Sim_FloatArray for testing.

The Node id is the unit the driver subscribes to, and the node itself decides how its variables read. Every variable on an array-valued node reads the element at its own position, whether it is an element of a Variable Array, a row of a UDT array member whose Node id has no {Index} token, or a single variable, which reads the first element. Variables on a scalar node read the scalar. A variable at a position above 0 on a scalar node, a position the array does not have, a Node id the server rejects and a node that reports a bad status all show the FormatError or Unknown status with one entry in the System Log Viewer, and a write to such a variable is refused with an entry as well.

Notes

The channel state indicator on each device row shows the current connection status.

When Enable Secure Channel is active, the client certificate is selected with Subject Name and the OPC UA server must trust this certificate for the connection to succeed.

On Windows, install the certificate with its private key in the Windows certificate store under Local Computer / Personal, and make sure the EnvisionSCADA service account can read the private key.

On Docker, the certificates are kept in folders under /app/certs/pki: own (client certificate and private key), trusted (trusted server certificates), issuers (CA certificates) and rejected (rejected server certificates). On the first secure connection EnvisionSCADA creates a self-signed client certificate in the own folder, or uses the certificate with the same subject name that is already there. Mount /app/certs as a volume so the certificates are kept when the container is recreated, otherwise a new certificate is created and the OPC UA server has to trust it again. The device events show which client certificate was loaded or created.

Subscriptions allow different update rates for different groups of variables. Assign fast-changing process values to a subscription with a short publishing interval and slow-changing configuration values to a subscription with a longer interval. This optimizes network and server load.

Variables are referenced at runtime using the format DeviceName.VariableName, for example OPCUA1.Pump1_Speed.

A variable starts with the Unknown status and becomes Good with the first value notification the server sends for its Node id. A variable whose Node id the server rejects, or whose node never publishes a value, keeps the Unknown status with its initial value, so a wrong Node id is visible on the page status icon, in the Status field of the runtime API and on the OPC UA server instead of reading as 0 with a Good status. See the Variable Status article for the full list of status values.