Persisting Runtime Toolbar and Curve Changes in WinCC OnlineTrendControl for SIMATIC PCS 7

Modifications made to the WinCC OnlineTrendControl during runtime—such as adding export buttons, selecting curves, or rescaling axes—are lost upon OS restart because the control's 'Online Configuration' property is set by default to 'Discard online changes'. In SIMATIC PCS 7, runtime alterations can be persisted by changing the Online Configuration setting in Graphics Designer to 'Save permanently' or 'Save for this session', or by utilizing the standard PCS 7 Trend Group functionality. In multi-client architectures, using PCS 7 Trend Groups (@TRG_...) is the recommended method to save operator curve layouts independently of base screen files.

WinCC OnlineTrendControl Runtime Behavior and Persistence Modes

The WinCC OnlineTrendControl (an ActiveX/.NET-based display element used across SIMATIC PCS 7 operator stations) allows operators to visualize live and historical process values (f(t)).

During commissioning or operational shifts, operators frequently customize trend displays:
* Enabling toolbar icons (such as Export Data to CSV, Select Trends, or Ruler / Statistics Tool).
* Changing axis scaling from auto-range to fixed ranges.
* Adding temporary archive tags for comparison.

By default, when the WinCC picture is closed, re-opened, or when the OS runtime is restarted, all customizations vanish and the control resets to its original static layout. This behavior is governed by the control's internal configuration retention policy.

Configuring the Online Configuration Property in Graphics Designer

To control whether modifications made during runtime persist permanently, open the screen in WinCC Graphics Designer and configure the control properties:

[WinCC Explorer -> Graphics Designer]
   │
   ├─► Open Target Picture (e.g., "Plant_Trends.pdl")
   ├─► Double-click: WinCC OnlineTrendControl
   ├─► In the Configuration Dialog, navigate to Tab: "Online Configuration"
   │
   ├─► Select Desired Retention Mode:
   │     • ( ) Discard online changes (Default: All modifications lost on picture change)
   │     • ( ) Save for this session (Retains changes until WinCC Runtime deactivates)
   │     • (•) Save permanently (Writes changes back to the PDL file on disk)
   │
   ├─► Navigate to Tab: "Toolbar"
   │     • Check: "Export Data" (Button ID 1007)
   │     • Check: "Select Trends" (Button ID 1006)
   │     • Check: "Save configuration" (Allows operator to manually trigger persistence)
   └─► Click Apply -> Save Picture (.pdl)

When set to Save permanently, any toolbar modifications or curve adjustments executed in runtime update the underlying PDL storage directly.

Persistence Architecture in Multi-Client and Web Navigator Systems

In distributed PCS 7 systems comprising redundant OS Servers and multiple OS Clients:
1. File Write Permissions: OS Clients do not typically have write access to shared project .pdl files residing on OS Server network shares. Therefore, attempting to execute 'Save permanently' on an OS Client will fail silently or trigger database permission errors.
2. Picture Caching: OS Clients utilize local picture caching (Temporary Internet Files or local project caches). Direct PDL writes will not propagate to peer client stations.
3. Web Navigator: Thin-client Web Navigator stations strictly forbid server-side file modifications from web sessions.

Trend Group Management via Standard Server Assignment

Because direct PDL saving is unsuitable for multi-client DCS architectures, Siemens PCS 7 incorporates the Trend Group mechanism:

Persistence StrategyScopeStorage LocationMulti-Client Compatible?Recommended Use CaseDiscard Online ChangesTransientNoneYesStatic, standardized overview screens that must never change.Save Permanently (PDL)WorkstationLocal .pdl fileNo (Single-station ES/OS only)Engineering test stations and standalone single-user systems.Save for this SessionSessionRuntime RAM bufferYesTemporary operator shift investigations that should clear at logout.PCS 7 Trend Groups (@TRG)Global / Multi-UserWinCC User Archive / SQL ServerYes (Fully Compatible)Production DCS environments; enables operators to recall custom trend sets on any client.

To utilize Trend Groups across clients, ensure that in WinCC Explorer on each OS Client, Server Data -> Standard Server -> Split Screen Wizard / User Archives is assigned to the primary OS Server.

Verification

To verify that OnlineTrendControl settings persist across runtime restarts:
1. Open WinCC Runtime on the operator station and navigate to the modified trend picture.
2. Verify that the Export Data and Select Trends toolbar buttons are visible and active.
3. Use the runtime toolbar to add a process curve or adjust the Y-axis span, then click the Save Configuration toolbar button (or save the layout as a named Trend Group).
4. Deactivate WinCC Runtime (WinCC Explorer -> File -> Deactivate), wait for all SQL processes to terminate, and reactivate Runtime.
5. Navigate back to the trend picture; confirm that all toolbar buttons, curve selections, and axis scalings are preserved exactly as configured.

Limitations and Operational Precautions

Avoid using 'Save permanently' on pictures that are part of the standard PCS 7 basic system library (e.g., @PG_APL_Trend.pdl or @screen.pdl). Modifying and permanently saving system PDLs risks corruption during the next OS Project Editor update or Service Pack installation. Always configure custom trend layouts in user-created pictures or store operator selections using named Trend Groups.

Engineer FAQ

Why does 'Save permanently' work on my ES but fail on an OS Client?

An OS Client reads picture files over the network or from local cache with read-only permissions. Writing back changes to the OS Server's project folder requires write permissions and will be blocked by standard Windows security policies.

How does an operator export trend data to CSV in runtime?

In Graphics Designer, enable the 'Export Data' icon in the OnlineTrendControl Toolbar tab. In runtime, clicking this button prompts the operator to select a directory and exports all visible curve coordinates to a .csv file.

Where are PCS 7 named Trend Groups stored?

Named Trend Groups are stored in the WinCC Runtime database within dedicated system tables and can be accessed via the standard PCS 7 Trend Group management dialog (@TRG_...).

Can I programmatically save trend configurations using VBScript or C-Script?

Yes. The WinCC OnlineTrendControl exposes ActiveX methods such as Save() and Load() which can be executed via VBScript attached to custom operator buttons.