Collecting All Bypassed Signals on a Dedicated Overview Graphic in SIMATIC PCS 7 APL

To collect all bypassed interlock and protection signals onto a single overview graphic in SIMATIC PCS 7 V8.1, utilize the Advanced Process Library (APL) feature where interlock blocks (Intlk02, Intlk04, Intlk08, Intlk16) expose active bypass statuses via output parameter BypAct. Engineers can assemble an overview screen displaying APL block icons configured with bypass indicators, deploy WinCC Alarm Logging filtered by the bypass message class, or implement the PCS 7 Measurement Point Browser to list all bypassed technological blocks across the plant hierarchy.

Bypass Architecture in the SIMATIC PCS 7 Advanced Process Library

In process automation plants, maintenance personnel and operations staff occasionally need to bypass process interlocks (such as high-level trip switches or valve limit check interlocks) during startup, instrument calibration, or equipment servicing. Unmonitored or forgotten bypasses present a severe process safety and operational hazard.

SIMATIC PCS 7 Advanced Process Library (APL) incorporates standardized bypass mechanisms within its interlock family:
* Intlk02 (FB 1824) – Interlock with 2 input signals
* Intlk04 (FB 1825) – Interlock with 4 input signals
* Intlk08 (FB 1826) – Interlock with 8 input signals
* Intlk16 (FB 1827) – Interlock with 16 input signals

Each interlock block permits individual inputs (In01 to In16) to be bypassed by an operator holding elevated authorization (Operation level 1102: Higher process controlling), provided the feature bit Feature.Bit2 (Separate evaluation of excluded and simulated interlock signals) is appropriately configured. When an input is bypassed, the interlock logic substitutes a healthy status (logical 1) for that input, preventing a plant trip, while latching a bypass state flag.

Data Structure of APL Interlock Bypass Signals

Every APL interlock block generates specific output status variables that indicate whether any connected input is currently bypassed:
1. BypAct (Output, STRUCT or BOOL): Active bypass indicator. Switches to TRUE (1) whenever at least one interlock input signal is excluded/bypassed.
2. BypProt (Output, BOOL): Protected bypass indicator. Indicates that bypass is active on an interlock tied to equipment protection (Protect).
3. Status1 / Status2 (Output, DWORD): Internal status word containing packed bit fields describing individual channel bypass states.
4. OS_Perm / OS_PermLog: Authorization vectors defining whether the logged-on user has rights to bypass individual signals.

In addition to interlock blocks, technological control blocks such as MotL (FB 1850), MotRevL (FB 1851), VlvL (FB 1899), and Vlv2WayL (FB 1897) evaluate connected interlock blocks. If an interlock input is bypassed, the motor or valve block icon on WinCC displays an orange/blue bypass badge, notifying operators that protective constraints have been overridden.

Methods for Centralizing Bypassed Signals on the OS

Plant operators require a single central location to view all active bypasses without clicking through hundreds of piping and instrumentation diagrams (P&IDs). Three primary architectures accomplish this in PCS 7:

Method 1: Dedicated Process Picture with APL Block Icons

Engineers create an overview graphic (e.g. @Bypass_Overview.pdl) within the WinCC Plant Hierarchy. Block icons for all plant interlocks (Intlk04, Intlk08) are placed on this graphic. When any interlock has an active bypass, the standard APL block icon dynamically highlights the bypass state. Clicking the icon directly opens the corresponding faceplate.

Method 2: WinCC Alarm Logging Message Filter

Whenever an operator sets an interlock bypass, APL generates an operator prompt/audit message in WinCC Alarm Logging. By embedding a WinCC AlarmControl into a dedicated graphic and filtering by message class (Operation Message / Process Control Message) or message text *Bypass*, all bypass operations appear chronologically with timestamps and operator user IDs.

Method 3: PCS 7 Measurement Point Browser

Starting in PCS 7 V8.0 and enhanced in V8.1, the Measurement Point Browser (@Overview1.pdl toolbar button) allows operators to query all blocks across the entire plant filtered by status attributes, such as 'Bypassed', 'Simulated', or 'Interlocked'. This method requires zero graphic engineering.

Bypass Visualization Comparison Matrix

The following matrix evaluates the three bypass collection methods available in SIMATIC PCS 7:

Evaluation AttributeDedicated Overview GraphicWinCC Alarm Control FilterMeasurement Point BrowserEngineering EffortModerate (Icon placement)Low (Alarm control configuration)Zero (Native out-of-the-box feature)Real-Time Dynamic UpdateInstantaneous via tag connectionEvent-driven on alarm occurrencePolled on demandOperator NavigationOne-click jump to faceplateJump to loop-in-alarmDirect faceplate callupPlant Hierarchy GroupingFully customizable layoutTabular list by timestampHierarchical tree by plant sectionAudit Trail IntegrationRequires separate trend/logFull historical audit trailReal-time active status onlyRecommended Use CaseOperations shift handover overviewCompliance and safety auditingRapid ad-hoc maintenance inspection

Step-by-Step Implementation of a Dedicated Bypass Overview Graphic

To build a dedicated real-time Bypass Overview screen:
1. Configure CFC Interlocks:
- In CFC, ensure all interlock blocks (Intlk04, Intlk08) have Feature.Bit2 = TRUE if excluded interlock status must be differentiated from simulation.
- Assign meaningful names and comments to interlock blocks to ensure clarity on OS faceplates.
2. Create Overview Picture in Plant Hierarchy:
- In SIMATIC Manager Plant View, create a new hierarchy folder titled Diagnostics or Bypass Management.
- Insert a new WinCC graphic named Bypass_Overview.pdl.
3. Compile the OS:
- Run OS Compilation (Compile OS). Ensure Generate block icons is executed for the project.
4. Populate the Graphic in Graphics Designer:
- Open Bypass_Overview.pdl in WinCC Graphics Designer.
- Insert block icons for interlocks. Alternatively, place dynamic status indicators (custom status lamps or SVG symbols) linked directly to the BypAct tag of each interlock instance (e.g. Plant1/Unit01/Reactor_Intlk.BypAct).
- Group the indicators by physical unit (e.g. Raw Material Storage, Reactor 1, Separation Unit).
5. Configure Faceplate Navigation:
- Use the WinCC Dynamic Wizard Connect picture to picture tree or configure a mouse-click event on each indicator calling OpenFaceplate for the target interlock block.

Verification

Verify bypass collection functionality in runtime:
1. Open the WinCC Runtime interface on the OS Client or Server.
2. Navigate to an operating unit and open an interlock faceplate (e.g. Intlk04).
3. Log in with user credentials possessing authorization Level 1102.
4. Set an active interlock input to Bypassed. Verify the input turns to bypass state and BypAct transitions to 1.
5. Open the Bypass_Overview.pdl screen and verify the corresponding indicator immediately illuminates.
6. Open the PCS 7 Measurement Point Browser, select the filter for Bypassed Blocks, and confirm the interlock appears in the active list.
7. Reset the bypass in the faceplate and confirm all overview displays return to normal unbypassed states.

Limitations and Operational Precautions

Operating bypasses without strict management-of-change (MOC) protocols can defeat safety interlocks and damage machinery.
Bypassing signals on standard APL interlocks does NOT bypass Safety Instrumented Systems (SIS) managed by S7 F Systems; fail-safe bypasses must be governed separately via Safety Matrix or fail-safe logic.
The Measurement Point Browser queries tags over the terminal bus; setting excessively rapid refresh rates on large plants (>10,000 tags) can introduce transient CPU load on OS servers.

Engineer FAQ

Which user authorization level is required to bypass an APL interlock signal?

By default, bypassing an interlock in the APL requires authorization Level 1102 (Higher process controlling). This prevents standard field operators (Level 5 / Level 6) from overriding safety and operational interlocks without supervisor authorization.

Does the Picture Tree group display show an active bypass?

Yes. When configured, the PCS 7 standard Group Display (@PG_APL_...) propagates the bypass state up through the plant hierarchy tree, illuminating a distinct yellow/blue bypass indicator at the top-level area buttons.

Can I bypass an input if the interlock block is in Local or Out of Service mode?

When an interlock block is placed 'Out of Service' (OosAct = 1), all logic evaluation stops and outputs remain in a predefined safe state. Individual input bypassing is inactive in Out of Service mode.