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Configuring Operator Control Permissions and Command Locking on APL Valve Blocks in SIMATIC PCS 7

Configuring Operator Control Permissions and Command Locking on APL Valve Blocks in SIMATIC PCS 7

Restricting operator valve operation in SIMATIC PCS 7 while preserving position visualization requires configuring the Operator Permissions bitmask (OS_Perm) on Advanced Process Library (APL) valve blocks. Setting control signals like ModLiOp or LocalLi to 1 only changes control modes without permanently locking out operator commands. To completely disable open, close, and manual mode switching from the WinCC runtime faceplate, engineers must configure the OS_Perm structure in Continuous Function Chart (CFC) to withdraw operator authorization bits while maintaining active feedback limit switch monitoring.

Table of Contents

Operator Permission Architecture in APL Valve Blocks

In the SIMATIC PCS 7 Advanced Process Library (APL), valve function blocks—including VlvL (large valve), VlvS (small valve), Vlv2Way (two-way valve), and VlvAnL (analog valve)—implement an Operator Permissions architecture governed by the 32-bit input structure OS_Perm:

  • Granular Capability Masking: Rather than relying solely on global user login levels, OS_Perm provides bit-level control over every individual operator interaction supported by the block faceplate.
  • Bit Assignment in Valve Blocks:
  • Bit 0: 1 = Operator can open the valve / switch to Open state.
  • Bit 1: 1 = Operator can close the valve / switch to Closed state.
  • Bit 2: 1 = Operator can reset the valve after a trip or interlock.
  • Bit 3: 1 = Operator can switch to Manual mode (ManModOp).
  • Bit 4: 1 = Operator can switch to Automatic mode (AutModOp).
  • Runtime Faceplate Enforcement: When an operator opens the valve faceplate in WinCC, the APL runtime script evaluates the active OS_Perm bitmask. If a permission bit is 0, the corresponding command button (e.g., Open or Close) is rendered grayed-out and disabled.

Why ModLiOp and LocalLi Do Not Prevent Operator Manipulation

Engineers frequently attempt to restrict operator control by manipulating mode selection pins:

  • ModLiOp (Mode Link / Operator): Setting ModLiOp = 1 enables automatic/manual mode switching via controller logic inputs (AutModLi, ManModLi). However, if the block remains in Manual mode, the operator can still issue manual open and close commands from the faceplate unless explicitly locked.
  • LocalLi (Local Setting via Interconnection): Setting LocalLi = 1 switches the block into Local operating mode. In Local mode, the valve expects digital inputs from a field control station. However, without restricting operator permissions, operators can still switch modes or intervene if tracking parameters (LocalSetting) permit.

To make it impossible for an operator to alter valve position under any circumstance while continuing to display live limit switch positions, OS_Perm must be explicitly configured.

Step-by-Step Configuration of the OS_Perm Bitmask

Follow this engineering procedure in Continuous Function Chart (CFC) to lock out operator control:

Step 1: Expose the OS_Perm Parameter in CFC

  1. Open the CFC chart containing the target valve block (VlvL).
  2. Double-click the block or right-click and select Object Properties.
  3. In the Properties window, select the Inputs/Outputs tab.
  4. Locate the input parameter named OS_Perm (Data type: STRUCT or DWORD).
  5. Ensure the parameter visibility is set to active (check the box under the I/O column to display it on the CFC block boundary).
  6. Click OK.

Step 2: Configure the Permission Bits

  1. Expand the OS_Perm structure on the block pin or expand its individual sub-elements.
  2. Set the following bits to 0 (FALSE):
    * OS_Perm.Bit0 = 0 (Disable operator Open command)
    * OS_Perm.Bit1 = 0 (Disable operator Close command)
    * OS_Perm.Bit3 = 0 (Disable operator Manual mode switch)
  3. Set OS_Perm.Bit4 = 1 or leave automatic mode enabled so the block operates under programmatic control.
  4. If configuring as a raw 32-bit hex value, set OS_Perm to exclude bits 0, 1, and 3.
  5. Alternatively, connect a logic block (such as an internal bitmask constant or Sel01 block) to dynamically revoke permissions during specific plant operating phases.

Configuring Op_Level and User Authorization Rights

In addition to OS_Perm, the engineer can restrict access using the technological operator authorization parameter Op_Level:

  1. In the block properties, locate the parameter Op_Level (Operator Level).
  2. Assign Op_Level to a high security tier (e.g., Level 7: Process Operations Specialist, or Level 9: Engineer).
  3. In WinCC User Administrator, configure standard plant operators with Level 5 (Process Operations).
  4. Because standard operators lack Level 7/9 rights, WinCC automatically prevents interaction with the valve faceplate buttons, restricting the view to read-only monitoring.

Verification

Confirm that operator command locking is fully functional:

  1. WinCC Runtime Faceplate Inspection:
    * Open the WinCC process graphic in runtime.
    * Click the valve icon to launch the APL faceplate.
    * Confirm that the Open and Close buttons are grayed out, disabled, and unresponsive to mouse clicks.
  2. Position Monitoring Check:
    * Toggle the physical or simulated open limit switch (FbkOpen) and closed limit switch (FbkClose).
    * Confirm that the valve icon dynamically updates between Closed (gray/green), Opening (flashing), and Open (green/white) states in real time.
  3. Authorization Check:
    * Log in with standard operator credentials; verify that manual commands remain blocked.

Limitations and Operational Precautions

  • Emergency Override Constraints: If an operator must be able to open or close the valve during an emergency, revoking OS_Perm bits prevents manual intervention from SCADA. Emergency bypasses must be handled via hardwired interlocks or supervisory overrides.
  • Reset Capability: Ensure OS_Perm.Bit2 (Reset) is evaluated carefully. If an operator cannot reset an interlock fault, the valve will remain locked out until a supervisor intervenes.
  • Online Delta Download: Modifying OS_Perm parameter values can be performed online in CFC and downloaded via changes only without stopping the controller.

Engineer FAQ

  • What is the primary parameter for restricting operator control in APL valve blocks?
    The 32-bit input structure OS_Perm, which defines specific operator permissions for opening, closing, and mode selection.
  • Why did setting ModLiOp = 1 fail to prevent the operator from clicking Open and Close?
    ModLiOp only transfers automatic/manual mode switching to program logic; if the valve is in manual mode, the operator can still issue open/close commands.
  • Can I make an actuated valve act like a purely monitored manual valve?
    Yes, by configuring OS_Perm to disable Bits 0 and 1 (Open/Close), the block functions as a read-only indicator of limit switch positions.
  • What is the function of OS_Perm.Bit3?
    OS_Perm.Bit3 authorizes the operator to switch the valve from Automatic mode to Manual mode. Disabling it locks the valve in Automatic mode.
  • Does modifying OS_Perm require compiling the WinCC OS?
    No, OS_Perm is evaluated dynamically by the AS block and read cyclically by the WinCC APL faceplate scripts.
  • What block parameter defines the required WinCC authorization level for a valve?
    The Op_Level parameter, which maps faceplate control operations to WinCC User Administrator authorization levels (1 to 16).
  • Can OS_Perm bits be altered dynamically by PLC logic?
    Yes, by interconnecting OS_Perm to a dynamic bitmask generated by logic blocks, permissions can be granted or revoked based on plant mode.
  • Does restricting OS_Perm disable automatic interlocks?
    No, controller interlocks (Intlock, Protect) operate entirely independently of operator permissions.
  • What happens to the WinCC faceplate when all OS_Perm bits are set to 0?
    All interactive command buttons appear grayed out with a lock icon, transforming the faceplate into a pure monitoring display.
  • Is OS_Perm available on legacy standard library blocks like FB73?
    Standard legacy blocks like FB73 use simpler authorization schemes; OS_Perm is a feature of the PCS 7 Advanced Process Library (APL).

Technical References

  • Siemens Industry Online Support (SIOS) Portal: SIMATIC PCS 7 Advanced Process Library (APL) Function Manual (Entry ID: 109760968).
  • SIMATIC PCS 7 APL Operator Permissions and OS_Perm Bitmask Reference Guide.
  • WinCC User Administrator Configuration Manual, Siemens AG.

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Related Tags

PCS 7, APL, Valve Block, VlvL, OS_Perm, Operator Permissions, WinCC Faceplates, CFC Configuration

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