Essential PCS 7 Engineering: S7-H NetPro Connections, PLCSIM Testing, and Analog Scaling

To configure essential PCS 7 communications and signal conditioning across NetPro, S7-PLCSIM, and CFC, engineers must adhere to three foundational rules. First, communication between a WinCC OS and a redundant S7-400H automation station requires configuring a single 'S7 fault-tolerant connection' in NetPro, which automatically creates redundant sub-connections across all CP 443-1 cards. Second, because S7-PLCSIM cannot simulate S7 fault-tolerant or Named connections, testing AS-OS communications in simulation requires temporarily replacing the connection with a standard 'S7 connection'. Third, raw analog input words (PEW) should always be routed through the APL channel driver Pcs7AnIn, which scales raw integer values (0–27648) into engineering units (Scale.Low to Scale.High), provides quality status (ST), and populates WinCC faceplates.

Configuring S7 Fault-Tolerant Connections in NetPro

In SIMATIC PCS 7, linking an operator station (OS) to a redundant S7-400H automation station (AS) requires establishing an S7 fault-tolerant connection (S7-H connection) within NetPro:

Open NetPro in SIMATIC Manager.
Select the WinCC Application object within the OS PC station.
In the connection table, insert a new connection:
* Connection Partner: Select the redundant CPU S7-400H station.
* Type: Select S7 fault-tolerant connection.
NetPro automatically establishes a logical multi-path connection:
* If both the AS and OS have dual Industrial Ethernet network cards (e.g., CP 1623 on OS and dual CP 443-1 on AS), NetPro provisions up to 4 redundant physical sub-connections.
* If one physical cable or switch fails, SIMATIC NET seamlessly switches to an alternate path in milliseconds without dropping WinCC tags or generating operator alarms.

Overcoming S7-PLCSIM Simulation Constraints with Fault-Tolerant Links

When testing plant logic offline, process engineers frequently encounter compilation or download errors when attempting to load S7 fault-tolerant connections into S7-PLCSIM:

The Limitation: S7-PLCSIM simulates the CPU instruction set but does not emulate the complex multi-channel communication stack of CP 1623 cards or S7-H redundancy management. PLCSIM does not support S7 fault-tolerant connections or Named Connections.
The Engineering Workaround:
1. In NetPro, create a separate test connection of type S7 connection (standard non-fault-tolerant) between the OS WinCC Application and CPU 0 of the AS.
2. In the OS WinCC Tag Management, map the S7 Protocol Suite driver to the standard S7 connection.
3. PLCSIM can now download the connection table and exchange tags with WinCC simulation without communication errors.
4. Restore the S7 fault-tolerant connection prior to final commissioning on physical hardware.

Analog Input Scaling and Normalization via APL Pcs7AnIn Driver

Directly connecting raw peripheral input words (e.g., PEW50) to control blocks (like MotL or PIDConL) is an architectural anti-pattern in PCS 7. All raw hardware inputs must be processed through the APL channel block Pcs7AnIn:

Hardware Interconnection: Connect the peripheral address PEW50 to the PV_In input of Pcs7AnIn.
Engineering Range Configuration:
* Set Scale.High to the sensor maximum (e.g., 150.0 A for motor current).
* Set Scale.Low to the sensor minimum (e.g., 0.0 A).
Unit Code Assignment: Set the PV_Unit parameter to the standardized integer code (e.g., 1120 for Amperes).
Driver Wizard Generation: During CFC compilation with 'Generate Module Drivers' enabled, PCS 7 automatically wires the diagnostic pins (Mode, DataXchg, MS) to system @ charts, guaranteeing that wire breaks or module failures assert Bad = TRUE and switch the signal status to invalid (16#00).

Diagnosing AS-to-OS Connection Health in WinCC Runtime

To inspect communication health between the OS server and AS controllers during commissioning:

WinCC Channel Diagnosis:
* On the active OS Server, open Windows Start Menu -> Siemens Automation -> SIMATIC -> WinCC -> WinCC Channel Diagnosis.
* Under Channels / Connections -> SIMATIC S7 Protocol Suite -> Named Connections, inspect the status of each AS connection.
* Status must show 'OK / Ready' with actively incrementing read/write counters.
WinCC Explorer Driver Status:
* In WinCC Explorer, click Tools -> Status of Driver Connections.
* A diagnostic window displays all configured AS stations, showing connection state, cycle times, and tag transaction counts.
NetPro Online Status:
* In NetPro, select the AS CPU and click PLC -> Activate Connection Status to observe live green connection lines.

Communication Connection and Driver Specification Matrix

The following table outlines the communication types, simulation compatibility, and channel block roles:

Connection / Driver ComponentArchitecturePLCSIM Compatible?Redundancy SupportPrimary FunctionS7 Fault-Tolerant ConnectionNetPro S7-H LinkNo (Hardware only)Up to 4 physical sub-pathsHigh-availability AS-to-OS communicationsStandard S7 ConnectionNetPro S7 LinkYes (Supported)Single physical pathNon-redundant AS or PLCSIM offline testingPcs7AnIn Channel BlockAPL CFC BlockYesModule redundancy supportScales raw PEW (0–27648) to engineering unitsPcs7DiIn Channel BlockAPL CFC BlockYesChannel flutter filteringDebounces raw digital inputs with quality codesWinCC Channel DiagnosisWinCC Diagnostic ToolYesReports sub-connection statesReal-time driver health and telegram counters

Adhering to standard driver conventions ensures robust plant diagnostics and predictable control behavior.

Verification

To verify communications and scaling:
1. In HW Config and NetPro, verify that the S7 fault-tolerant connection shows 'Compiled: 0 Errors'.
2. Download hardware configuration and CFC charts to the controller.
3. In CFC test mode, open Pcs7AnIn; verify that forcing a raw input of 13824 on PV_In yields an exact 50% value on PV_Out with valid signal status (ST = 16#80).
4. In WinCC Channel Diagnosis, verify that the AS connection reports state 'Ready' with zero telegram errors.
5. In WinCC Runtime, verify that the motor current faceplate renders the scaled engineering value with proper units.

Limitations and Operational Precautions

Never download S7 fault-tolerant connections to S7-PLCSIM; doing so causes download rejection errors.
Always use Pcs7AnIn or Pcs7DiIn channel drivers to process I/O addresses; bypassing drivers disables automated diagnostic generation.
Ensure CP 443-1 communication processors have updated firmware to support maximum concurrent S7-H connections.
Always validate final license quantities, module availability, and MLFBs against the applicable Siemens catalog and authorized distributor quotation.

Engineer FAQ

Why does NetPro give an error when creating an S7-H connection with an IE General card?

S7 fault-tolerant connections on the OS side require either a dedicated CP 1623 / CP 1613 communications processor with the 'BCE / Hardnet-IE S7-REDCONNECT' license or standard network cards running the Softnet S7-REDCONNECT package with compatible PCS 7 releases.

How do I extract a single bit from a 16-byte input block from a protection relay (SIPROTEC)?

Create a custom SCL block that reads the 16 bytes via an ANY pointer or ARRAY[0..15] OF BYTE, and access the desired bit internally using boolean slicing (e.g., MyBit := InputBytes[0].%X0;).

Can an S7-400 communicate directly with another S7-400 without WinCC?

Yes. Cross-controller communication can be implemented using PCS 7 AS-Wide Interconnections directly in CFC, or via configured S7 connections in NetPro utilizing BSEND/BRECV blocks.