Configuring Dynamic Limits on WinCC User Archive I/O Fields

Overview

WinCC 7.x User Archives store process data in ODBC-backed tables that the HMI runtime reads and writes via UA tags, the User Archive Table Control, and the uasql API. When you create a column with the User Archive configuration wizard, the User Archive Field Creation Wizard lets you enter a static Minimum and Maximum value that the runtime enforces when the operator edits the field in the table view. These static bounds are baked into the configuration database at compile time, so they cannot be changed at runtime by the operator.

This article shows how to replace those static bounds with dynamic limits driven by WinCC tags. Three production-ready methods are documented end to end:

1. Dynamizing the LowLimit / HighLimit properties of a stand-alone I/O field that writes to a User Archive column.
2. Scripting a pre-write validation routine on the User Archive Table Control's Apply event that compares the operator's value against current tag-driven limit pairs and rejects out-of-range edits.
3. Using the User Archive C-API / uasql commands from a global VBScript action to perform server-side validation and write-back.

Prerequisites

Why the Wizard Limits Are Static

The User Archive Field Creation Wizard writes the MinValue and MaxValue columns into the configuration archive (the read-only UA_CONFIG schema). At runtime, the table control consults these values once when constructing the editor cell for the column; they are not re-evaluated on every keystroke. Consequently, even if you change them via the WinCC UserArchiveControl configuration dialog at runtime, open editors already in place will continue to use the original bounds.

To produce bounds that do follow HMI tags, you must move the validation outside of the wizard metadata. The two layers at which this can be done cleanly are:

• The field property layer of a stand-alone I/O field that has been linked to a User Archive tag.
• The script layer invoked by the table control's BeforeWrite / AfterChange / Apply events.

Method 1 — Tag-Dynamized Limits on a Stand-alone I/O Field

This is the simplest and most reliable technique. You keep the User Archive Table Control as a read-only overview, then add an explicit I/O Field for each field the operator must change. The I/O field's LowLimit and HighLimit properties accept direct tag dynamization.

Step 1 — Create the limit tags

Open the Tag Management and add two internal 32-bit float tags:

• SP_Archive_MinValue (data type: Float, length: 4)
• SP_Archive_MaxValue (data type: Float, length: 4)

Both tags will be writable from the operator screen so the bound can be changed live.

Step 2 — Configure the User Archive tag

In the User Archive editor, define a column Setpoint with:

• Type: Floating-point number (32-bit IEEE)
• Min / Max: set to the broadest engineering range (e.g. -1.0E+30 to 1.0E+30) — the wizard values are placeholders only, the actual enforcement happens in the I/O field.
• Archive: SP_Setpoint

Step 3 — Drop the I/O field on the screen

1. From the Smart Objects palette, place an I/O Field on the process screen.
2. In the configuration dialog, set:
   • Tag: select SP_Setpoint (the archive tag).
   • Data format: 999.99 (or your engineering format).
3. Switch to the Properties tab and expand Limits.

Step 4 — Dynamize LowLimit and HighLimit

1. Click the small light bulb next to Low limit value > Limit value. Choose Tag and select SP_Archive_MinValue.
2. Repeat for High limit value > Limit value and select SP_Archive_MaxValue.
3. Activate Apply on input for both.

At runtime, when the operator enters a value outside the current range of those tags, WinCC rejects the input, flashes the field red, and (optionally) triggers a horn or event depending on the messaging configuration. The User Archive itself is never written with an invalid value.

Step 5 — Provide an operator control for the limits

Drop two additional I/O fields, link them to SP_Archive_MinValue and SP_Archive_MaxValue, and (for safety) set their own hard static limits to the broadest engineering range to prevent the operator from typing NaN or absurdly large numbers.

Method 2 — VBScript Pre-Write Validation on the Table Control

When the operator must edit values directly in the table view (not through stand-alone I/O fields), dynamize the I/O field properties is not possible because the table's edit cell is generated by the control itself. In that case, attach a VBScript action to the table control that runs before the write is committed to the archive.

Step 1 — Expose the table control's events

1. Right-click the User Archive Table Control and select Properties > Events.
2. Configure the Apply event (or ApplyData on older controls) with the right mouse button > VBS Action.

Step 2 — Write the validation routine

' --- vbs in Apply event of the User Archive Table Control ---
Option Explicit

Dim oUACtl, oReadRow, sFieldName, vNewValue
Dim dMin, dMax, dVal

Set oUACtl = ScreenItems("UACTL_Setpoints")

' Resolve limit tags
dMin = HMIRuntime.Tags("SP_Archive_MinValue").Read
dMax = HMIRuntime.Tags("SP_Archive_MaxValue").Read

' Loop every edited row in the pending buffer
For i = 1 To oUACtl.GetPendingRowCount()
    sFieldName = "Setpoint"
    vNewValue = oUACtl.GetPendingCellValue(i, sFieldName)
    If IsNumeric(vNewValue) Then
        dVal = CDbl(vNewValue)
        If dVal < dMin Or dVal > dMax Then
            HMIRuntime.Trace "UA validation: row " & i & " " & _
                sFieldName & "=" & dVal & " outside [" & dMin & "," & dMax & "]" & vbCrLf
            oUACtl.RejectPendingRow i, vbTrue   ' cancel write of this row
            HMIRuntime.Alarm "ArchiveSetpointOutOfRange", _
                "Value " & dVal & " rejected. Limits: " & dMin & "..." & dMax
        End If
    Else
        oUACtl.RejectPendingRow i, vbTrue
    End If
Next

' Final commit if no rejections
If oUACtl.GetPendingRowCount() > 0 Then
    oUACtl.ApplyPending ' WinCC 7.5 SP1 and later
End If

Important behavioral notes:

• RejectPendingRow requires WinCC 7.5 SP1 Update 1 or later. On older builds, use oUACtl.CancelPending to drop the whole edit buffer.
• GetPendingCellValue returns the value as Variant; always convert with CDbl before comparison.
• The alarm number ArchiveSetpointOutOfRange must be defined in WinCC Alarm Logging beforehand.

Method 3 — Direct uasql Validation with Server-side Stored Procedures

For installations running against Microsoft SQL Server, the cleanest enforcement is server-side. Define a CHECK constraint that references a separate configuration table, and update that table from WinCC via uasql.

Step 1 — Define the dynamic limit table

CREATE TABLE dbo.ArchiveLimits (
    ArchiveName NVARCHAR(64) NOT NULL PRIMARY KEY,
    FieldName   NVARCHAR(64) NOT NULL,
    MinValue    FLOAT NULL,
    MaxValue    FLOAT NULL
);

Step 2 — Add a CHECK constraint to the data table

ALTER TABLE dbo.UA_Setpoints
ADD CONSTRAINT CK_Setpoint_Range CHECK (
    Setpoint >=
        ISNULL((SELECT MinValue FROM dbo.ArchiveLimits
                WHERE ArchiveName='UA_Setpoints' AND FieldName='Setpoint'), -1E+30)
    AND Setpoint <=
        ISNULL((SELECT MaxValue FROM dbo.ArchiveLimits
                WHERE ArchiveName='UA_Setpoints' AND FieldName='Setpoint'),  1E+30)
);

Step 3 — Update limits from a VBScript action

Dim sCon, sSql, oConn, oCmd

sCon = "Provider=SQLOLEDB;Data Source=WINCC_SRV;Initial Catalog=WinCC;Integrated Security=SSPI;"
sSql = "UPDATE dbo.ArchiveLimits SET MinValue=?, MaxValue=? " & _
       "WHERE ArchiveName='UA_Setpoints' AND FieldName='Setpoint';"

Set oConn = CreateObject("ADODB.Connection")
oConn.Open sCon
Set oCmd = CreateObject("ADODB.Command")
Set oCmd.ActiveConnection = oConn
oCmd.CommandText = sSql
oCmd.Parameters.Append oCmd.CreateParameter("Min", 5, 1, 8, _
    HMIRuntime.Tags("SP_Archive_MinValue").Read)
oCmd.Parameters.Append oCmd.CreateParameter("Max", 5, 1, 8, _
    HMIRuntime.Tags("SP_Archive_MaxValue").Read)
oCmd.Execute , , 128        ' 128 = adExecuteNoRecords
oConn.Close

This pattern has the advantage that the constraint is enforced even for direct SQL writes (for example from a script or a third-party SCADA). It also works when the WinCC project is part of a redundant server pair, because the limits are stored in the database rather than in tag memory.

Parameter Mapping Reference

Verification Procedure

1. Compile and download the project to the runtime.
2. Open the screen with the I/O field (Method 1) or the table control (Method 2).
3. Change SP_Archive_MinValue to 10 and SP_Archive_MaxValue to 50 via the operator limit fields.
4. Try entering 5 in the Setpoint I/O field (or table cell). The value must be rejected and the field must show the violation marker.
5. Enter 25; the value must be accepted.
6. Inspect the User Archive database with the WinCC UserArchive editor or via SQL: SELECT Setpoint FROM UA_Setpoints;. Confirm that only values inside [10, 50] are present.
7. Open the WinCC Diagnostics window — Apdiag.exe — and filter on ua_ events. Confirm that no warning UA_RANGE_VIOLATION is logged.

Troubleshooting Matrix

Field-Engineering Notes

• The wizard static values still matter when the archive is edited through WinCC Archive Connector or a third-party OPC UA client that bypasses the I/O field. Leave the wizard bounds at the broadest engineering range, and apply the operational envelope at the HMI layer.
• On redundant WinCC Server pairs, keep the limit tags in internal tag memory and replicate them with Tag Synchronization in the redundancy configurator. Otherwise the standby server will display stale limits after a failover.
• When the operator is allowed to edit limits, log every change to SP_Archive_LimitLog with a VBScript action tied to the limit I/O fields. This satisfies FDA 21 CFR Part 11 / EU Annex 11 audit requirements commonly seen in regulated plants.
• For multilingual sites, the runtime messages raised by the alarm number ArchiveSetpointOutOfRange must exist in every configured language, otherwise the operator sees the WinCC internal English text instead of the translated one.
• If the User Archive is configured on a remote SQL Server, the connection string in Method 3 must use Trusted Connection with the WinCC Runtime service account, not the engineer account.

FAQ