Configuring Analog and Modulating Control Valves in PCS 7 Using APL VlvAnL

To command an analog modulating control valve in SIMATIC PCS 7, deploy the APL function block VlvAnL (FB1896) in Continuous Function Chart (CFC). VlvAnL manages continuous position setpoints (0-100%) and position feedback (MV) while providing integrated manual, automatic, and tracking modes. Interconnect manipulated output parameter MV_Out to an analog output driver (Pcs7AnOu), connect field position feedback to MV via Pcs7AnIn, and route external setpoints from upstream controllers (PIDConL) or SFCs to SP_Ext. If the valve lacks discrete limit switches, configure parameters NoFbkOpen = 1 and NoFbkClose = 1 to prevent spurious feedback discrepancy alarms.

APL Valve Control Blocks: VlvAnL vs VlvPosL Selection

In the SIMATIC PCS 7 Advanced Process Library (APL), modulating and positional valves are automated using two distinct function blocks:

VlvAnL (Analog Control Valve - FB1896): Designed for pneumatic, hydraulic, or electro-mechanical modulating valves commanded via a continuous 4-20 mA, 0-10 V, or digital fieldbus (HART, PROFIBUS PA, PROFINET) positioner setpoint. It regulates continuous opening percentages ($0.0\text{ to }100.0\%$) and evaluates analog position feedback.
VlvPosL (Positioning Valve - FB1897): Designed for motorized actuator valves (such as AUMA, Rotork, or Limitorque) that accept discrete digital pulse commands (Open, Close, Stop) while returning continuous potentiometer or 4-20 mA position feedback.

For standard modulating control valves, VlvAnL is the recommended industry standard.

Signal Interconnections and Core Operational Parameters

Operating VlvAnL in automated plant environments requires establishing proper signal routing:
- Manipulated Value Output (MV_Out): The continuous output signal ($0-100\%$) routed to the Pcs7AnOu driver block, which transmits the raw count to the analog output module.
- Position Feedback (MV): The measured valve stem position ($0-100\%$) provided by Pcs7AnIn.
- Setpoint Selection: In Automatic mode, VlvAnL tracks SP_Ext (e.g., connected to PIDConL.MV). In Manual mode, operators adjust SP_Int directly from the WinCC faceplate.
- Limit Switch Feedback: If the valve is equipped with end-position limit switches, connect them to FbkOpen and FbkClose. If no limit switches exist, engineers must assert NoFbkOpen = 1 and NoFbkClose = 1; otherwise, the block will generate feedback monitoring alarms whenever the valve moves away from end positions.

Parameter Configuration and Interconnection Architecture

The table below details the essential CFC pins, driver interconnections, and configuration roles for VlvAnL:

ParameterType / DirectionDefault ValueInterconnection Source / DestinationFunctional DescriptionMV_OutSTRUCT (REAL, ST) Output$0.0\%$Connect to Pcs7AnOu.PV_InCommanded valve position sent to field output.MVSTRUCT (REAL, ST) Input$0.0\%$Connect to Pcs7AnIn.PV_OutActual valve position feedback from transmitter.SP_ExtSTRUCT (REAL, ST) Input$0.0\%$Connect to PIDConL.MV or SFC logicExternal setpoint used in Automatic mode.ModLiOpBOOL Input0Logic / SFC or operator constantSetpoint mode selection: 0 = Operator, 1 = Logic.AutModLiSTRUCT (BOOL, ST) Input0SFC / Cascade LogicSelects Automatic mode when ModLiOp = 1.NoFbkOpenBOOL Input0Parameterize 1 if no Open switchDisables open position limit switch monitoring.NoFbkCloseBOOL Input0Parameterize 1 if no Close switchDisables closed position limit switch monitoring.SafePosINT Input0Set 0 (Closed) or 1 (Open)Configures fail-safe position on interlock trip.

Step-by-Step CFC Engineering and Commissioning Procedure

Instantiate Blocks in CFC: Drag VlvAnL (FB1896) from the APL library catalog onto the chart. Insert Pcs7AnIn for position feedback and Pcs7AnOu for the command output.
Interconnect Channel Drivers:
- Connect field hardware addresses to the channel drivers (Pcs7AnIn.PV_In and Pcs7AnOu.PV_Out).
- Interconnect Pcs7AnIn.PV_Out -> VlvAnL.MV.
- Interconnect VlvAnL.MV_Out -> Pcs7AnOu.PV_In.
Configure Upstream Control Link: Interconnect the manipulated variable output of the upstream PID controller (PIDConL.MV) to VlvAnL.SP_Ext.
Parameterize Monitoring Limits:
- In the Object Properties of VlvAnL, configure MonTiDynamic (dynamic transit monitoring time) to match valve stroke time (e.g., $15.0\text{ s}$).
- If no discrete end-switches exist, set NoFbkOpen = TRUE and NoFbkClose = TRUE.
Compile and Download: Compile CFC with module drivers, download changes to the CPU in RUN mode, and execute OS compilation.
Commission Faceplate in WinCC: Open the WinCC faceplate for VlvAnL: test manual setpoint adjustments, verify smooth stem movement, and test bumpless transfer to automatic control.

Verification

Verify valve functionality through the following checks:
1. In WinCC Manual mode, enter a setpoint of $50.0\%$: verify that MV_Out reaches $50.0\%$, the physical positioner moves to mid-stroke, and feedback MV reads $50.0\% \pm 1.0\%$.
2. Switch the block to Automatic mode: verify that setpoint tracking switches smoothly to SP_Ext without output jumps (bumpless transfer).
3. Trigger an interlock input (Intlock or Protect): verify that the valve immediately drives to its configured safe position (SafePos) and generates an alarm on the OS.

Limitations and Operational Precautions

Ensure that stroke time scaling matches physical actuator performance. Forcing a rapid rate-of-change on large pneumatic actuators can cause positioner hunting or damage valve packings; utilize the internal gradient limiting parameters (SP_UpRaLim, SP_DnRaLim) within VlvAnL to clamp maximum travel velocity. Always ensure that fail-safe position parameter SafePos matches the physical spring-action failure mode (Air-to-Open vs Air-to-Close).