WinCC Tags Reference Comfort, Advanced, Professional, Unified

Overview

System tags are read-only or read/write variables automatically supplied by the WinCC runtime rather than by a PLC connection. In Siemens documentation they are typically named with the prefix @ (e.g. @CurrentUser, @LocalMachineName). The availability of these tags depends on the WinCC product line:

• WinCC Comfort / WinCC Advanced (TIA Portal) – used for SIMATIC HMI panels (Comfort, Mobile, and Basic lines) and PC-based Advanced runtime. System tags are not exposed in the HMI tag editor.
• WinCC Professional / WinCC V7.x (TIA Portal or legacy) – used for PC-based SCADA. A defined list of @-prefixed system tags is documented and selectable in the tag management.
• WinCC Unified (TIA Portal V16+) – the current RT Unified platform. System tags are documented under Configuring tags > System tags.

This reference consolidates the official list per product line, the syntax restrictions, the @CURRENTUSER behavior in Comfort-panel VBScript, and the workarounds to obtain equivalent values in Comfort/Advanced projects.

What a WinCC "System Tag" Actually Is

A system tag is an internal tag maintained by the WinCC runtime. Characteristics:

• Name always starts with @.
• Lifecycle is managed by the runtime (created at project start, deleted at runtime close).
• Read access is implicit in the tag browser and in scripts.
• Cannot be deleted by the user; cannot be renamed; cannot be re-declared.
• No connection to a PLC; the runtime is the data source.

Per the official WinCC Unified documentation (System tags (RT Unified)), the prefix is reserved by the runtime, which is why the tag editor rejects user tags that begin with @ in Unified projects.

WinCC Comfort and WinCC Advanced (TIA Portal V13 SP1 – V20)

In WinCC Comfort and WinCC Advanced the tag editor does not expose a "System tags" node. User queries in TIA Portal V14 SP1 confirming this behavior were answered officially by Siemens Support participants stating:

"System tags are not available in WinCC Advanced. In the SCADA systems SIMATIC WinCC and SIMATIC WinCC Professional you can use some system tags."

What Comfort/Advanced provides instead is a set of system functions callable from VBScript, from the "System functions" task card, and from the property interface of screens/objects:

These functions are listed in the TIA Portal help under Visualization > System functions. They are part of the Comfort/Advanced API since V11 and remain available in V14 SP1, V15.1, V16, V17, V18, and V20.

WinCC Professional and WinCC V7.x (SCADA)

In WinCC Professional (TIA Portal) and WinCC V7.x the tag editor contains a dedicated System tags folder that lists the available tags. The full catalog is documented in the WinCC Professional / WinCC V7.x help under Tag management > System tags. The most commonly used entries:

Syntax restrictions that apply in Professional and V7.x:

• Tag names are case-insensitive in scripts but appear mixed case in the editor.
• The @ prefix is reserved; attempting to create a user tag with the same name raises error 0x80040E14 (tag name invalid) at project compile.
• Numeric system tags are 16-bit signed by default; reading them in 32-bit VBScript variables requires an explicit conversion via CInt or CLng.
• Some tags are available only in the WinCC Explorer scope (e.g. @ServerName) and are not visible on a WinCC client until the client connection is fully established.

WinCC Unified (RT Unified, TIA Portal V16 – V20)

WinCC Unified re-introduces a documented System tags catalog. According to the official TIA Portal V20 help:

"System tags are internal tags that are required for internal management of the project. The system tag names always start with the '@' character."

Unified system tags are grouped under HMI Tags > System tags in the project tree. Representative entries (V20 documentation):

Unified restricts system tag usage in scripts to qualified access via the tag-prefix scope (e.g. Tags("@UAUserName").Read). Direct script access to local-process system tags such as cursor coordinates is no longer supported in V17 onward; use the new Screen.Items(...).Position properties instead.

Cross-Platform Comparison

Why @CURRENTUSER Appears to Work in WinCC Comfort Scripts

User reports in the field show inconsistent behavior when @CURRENTUSER is read in VBScript on a Comfort panel (e.g. KTP, TP, or Comfort Panel with WinCC Comfort V14 SP1):

• Reading HMIRuntime.Tags("@CurrentUser").Read inside a VBScript on a Comfort Panel returns an empty string on some firmware versions and the actual user name on others.
• The tag is not declared in the HMI tag list, so the runtime implicitly creates a transient internal variable with that name.
• If a project happens to declare a tag literally named @CurrentUser (which the tag editor will accept in Comfort because the prefix is not reserved), the script returns the value of the user-declared tag — not the runtime's user identity.

Recommended practice in Comfort/Advanced: do not rely on @CurrentUser for user identity. Use the documented system function GetUserName:

' VBScript on a Comfort Panel (WinCC Comfort V14 SP1+)
Dim sUser
sUser = HMIRuntime.SysFct.GetUserName()  ' Always returns the logged-in user
SmartTags("LoggedUser") = sUser           ' Write to a declared HMI tag

If the deployment must remain compatible with both Comfort panels and PC-based Advanced runtime, declare an internal HMI tag (e.g. LoggedUser) and populate it on screen start with the function above.

Workarounds for Comfort and Advanced Projects

Method 1 – System functions called on screen change

1. Open the screen in the Comfort/Advanced editor.
2. In the Events tab, add the GetUserName system function to the Loaded event of the root screen.
3. Set the function's output tag to an internal HMI tag of type Text (recommended length 32 characters).
4. Compile and download. The tag updates on every screen change.

Method 2 – Scheduled task in the scheduler

1. Open Schedules in the HMI project tree.
2. Create a new task running every 1 second.
3. In the VBScript editor, call HMIRuntime.SysFct.GetUserName() and write the result to a tag.
4. Use the tag in animations, I/O fields, or visibility expressions.

Method 3 – Project-wide variable initialized at runtime start

1. Add a global VBScript action attached to the Runtime start event.
2. Inside the action, query the user once and cache the result in an HMI tag.
3. Combine with GetGroupNumber and GetLanguage if group or language information is also required.

Tag Naming Conventions and Restrictions

Firmware and Version Compatibility

For Unified runtime the minimum panel firmware that supports the documented @UA* system tag set is image version 17.0.x (Unified Comfort V2 hardware) and 16.0.x (Unified Comfort V1 hardware). Older Unified Comfort panels running V15 image firmware do not expose the @UAConnectionState_X tags.

Diagnostics and Verification

Use the following steps to confirm that a system tag is being read correctly in a runtime project:

1. Open an I/O field on any screen in the project.
2. Set its process value to the system tag (e.g. @CurrentUser for Professional, @UAUserName for Unified, or the internal tag populated by GetUserName for Comfort/Advanced).
3. Configure the field as Output only with string display type.
4. Compile, download, and start the runtime.
5. Log in as a known user; the I/O field should show the user name within one update cycle (typically 250 ms for Comfort/Advanced, 100 ms for Unified).

If the field is empty:

• Confirm the tag prefix scope is correct (e.g. server-side tags on a WinCC client require the @ServerName: prefix).
• Open the WinCC diagnostics window (Tools > Diagnostics) and check the channel diagnostics for the system tag row.
• For Unified, run the Tag simulator from the runtime start menu and verify each @UA* tag against the documentation.

Common Errors and Resolution

Migration Notes: Comfort/Advanced → Unified

When porting a Comfort/Advanced project to WinCC Unified, the following substitutions are required:

Related Concepts Outside WinCC

For comparison only — the Ignition SCADA platform (Inductive Automation) uses the term "system tag" in a different sense: every Ignition tag is implicitly associated with a built-in System tag provider that exposes client, gateway, and historical metadata. Functions such as system.tag and system.tag.browse provide browse and read/write access to that provider. The System Tags lesson in Inductive University covers the provider model in detail. These concepts are not directly portable to WinCC, but the naming convention and the @ prefix reserved for internal use is industry-consistent across both platforms.

FAQ