Integrating PROFIBUS Diagnostic Repeaters (6ES7972-0AB01-0AX0) into PCS 7 and Maintenance Station Licensing

In SIMATIC PCS 7, the PROFIBUS Diagnostic Repeater (6ES7972-0AB01-0AX0) provides automated cable diagnostics, reflection detection, and line fault localization in meters. In STEP 7 HW Config, the repeater is inserted as a DP slave from the PROFIBUS-DP catalog. In CFC, compilation with 'Generate module drivers' automatically instantiates the diagnostic driver blocks (DP_REP / OB_DIAG1) and links them to the hardware address. For visualization, the repeater block icon appears automatically on the SIMATIC PCS 7 Maintenance Station (MS) in '@PCS7Typicals_Maintenance.pdl'. Operating the Diagnostic Repeater within a dedicated Maintenance Station requires a SIMATIC PCS 7 Maintenance Station Runtime License (Basic or Standard) and Maintenance Station Process Objects (MS POs); without an MS Server, standard DP alarms appear in WinCC AlarmControl using standard OS Runtime POs.

Executive Summary

Maintaining high network availability across extensive industrial PROFIBUS DP networks requires rapid localization of physical layer faults. The Siemens PROFIBUS Diagnostic Repeater (6ES7972-0AB01-0AX0) continuously monitors connected copper segments, detects impedance anomalies (such as severed cables, loose shield terminations, missing bus terminators, and reflections), and measures distance to the fault. However, configuring and visualizing these diagnostics within SIMATIC PCS 7 V9.0/V9.1 involves specific CFC block driver mechanics and software licensing rules. This article outlines the hardware integration workflow, CFC driver compilation, and Maintenance Station licensing prerequisites.

Architecture and Fundamental Mechanics

The Siemens Diagnostic Repeater (MLFB 6ES7972-0AB01-0AX0) combines RS 485 signal amplification with intelligent time-domain reflectometry (TDR) diagnostic hardware:
1. Hardware Integration: Configured in HW Config as a standard PROFIBUS DP slave connected to the DP master system of a CPU 410-5H or CP 443-5 Extended. It occupies 15 bytes of diagnostic and control memory (diagnostic address).
2. Automated Module Driver Generation: When CFC charts are compiled with 'Generate module drivers' enabled, the PCS 7 driver generator queries the hardware catalog and automatically instantiates the diagnostic block DP_REP (FB113 / FB184) and system supervisor OB_DIAG1. These blocks handle diagnostic interrupts (OB82) and station failure events (OB86).
3. Line Measurement Function: The controller or engineering tool triggers line measurement cycles. The repeater injects a high-frequency pulse into DP segments DP2 and DP3, measures reflections, and records cable topology tables in the repeater memory.
4. Visualization Mechanics: The Maintenance Station (MS) reads topology tables and fault logs via S7 communication. Standard graphic templates in @PCS7Typicals_Maintenance.pdl render repeater icons, displaying line integrity, segment status, and fault distance in meters.

Software Licensing Guardrails:
- Standard WinCC OS: If the repeater is monitored simply as an automation device generating standard alarm messages via ALARM_8P, no specialized license is needed beyond standard OS Runtime POs.
- Maintenance Station (MS): If the plant deploys an integrated SIMATIC PCS 7 Maintenance Station (MS Basic or MS Standard) to visualize diagnostic plant hierarchies, electronic device status, and line topology graphics, the MS Server requires a SIMATIC PCS 7 Maintenance Station Runtime License and corresponding MS Process Objects (MS PO). Sizing must be verified with an authorized Siemens distributor or the Siemens Industry Mall.

Step-by-Step Implementation Procedure

Configure Diagnostic Repeater in HW Config:
a. Open STEP 7 HW Config for the AS station.
b. From the Hardware Catalog, navigate to PROFIBUS-DP -> Network Components -> Diagnostic Repeater -> 6ES7 972-0AB01-0AX0.
c. Drag and drop the Diagnostic Repeater onto the PROFIBUS DP master line.
d. Assign a unique DP address (e.g., Address 3) and set subnet properties (baud rate 1.5 Mbps or configured rate).
e. Configure measuring segments (DP2 and DP3) according to physical cable routing.
f. Save and compile HW Config.
Perform PROFIBUS Line Topology Measurement:
a. In HW Config, select the Diagnostic Repeater and choose PLC -> Diagnostic Repeater -> Prepare Line Diagnostics.
b. Select 'Determine Topology'. The repeater pulses the bus and builds the segment slave table.
c. Verify that all downstream DP slaves are recognized at their approximate physical distances.
Execute CFC Driver Compilation:
a. Open SIMATIC Manager and launch the CFC Editor.
b. Execute Chart -> Compile -> Chart as Program....
c. Ensure 'Generate module drivers' is CHECKED.
d. The compiler automatically creates diagnostic chart @Diagnostics containing DP_REP and OB_DIAG1, interconnecting them to the repeater diagnostic address.
Configure Maintenance Station Visualization:
a. In SIMATIC Manager Plant View, ensure the Maintenance Station is configured.
b. Open Maintenance Station properties and execute 'Generate Diagnostic Screens'.
c. In WinCC Explorer, verify that @PCS7Typicals_Maintenance.pdl contains active block icons for the diagnostic repeater.
d. Execute an OS compilation to transfer diagnostic tags and alarm definitions.

Verification

In WinCC Runtime on the Maintenance Station, navigate to the Fieldbus Overview screen: confirm the Diagnostic Repeater icon displays a healthy green state.
Click the repeater block icon to open its faceplate: verify that Segment DP1, DP2, and DP3 report active communication.
Disconnect the bus connector from a downstream DP slave: verify that the repeater detects the cable reflection, asserts an alarm, and displays the estimated distance to the break (e.g., 'Fault at Segment 2, Distance: 42 meters').
Check the CPU Diagnostic Buffer: confirm OB82 records the diagnostic interrupt with clean event clearing upon reconnection.

Limitations and Operational Precautions

The line diagnostic reflectometry function operates only on segments DP2 and DP3; segment DP1 is an unmonitored feed segment. All devices connected to monitored segments must adhere strictly to PROFIBUS RS 485 transmission guidelines (maximum spur lines, proper 110-ohm active termination). Up to 31 slaves can be monitored per segment. Procurement of Diagnostic Repeaters and Maintenance Station licenses must be verified with an authorized Siemens distributor or the Siemens Industry Mall.

Engineer FAQ

Do I have to manually place the DP_REP block in a CFC chart?

No. When 'Generate module drivers' is executed during CFC compilation, PCS 7 automatically instantiates and wires the DP_REP block inside system diagnostic charts.

Does the Diagnostic Repeater require an extra license on a standard WinCC OS?

No. Standard alarm logging and basic device status monitoring require only standard PCS 7 OS Runtime PO licenses.

When is a dedicated Maintenance Station license required?

A Maintenance Station license (MS Basic or MS Standard) and MS POs are required if utilizing the integrated SIMATIC PCS 7 Maintenance Station for plant asset management and topology graphics.

What causes the Diagnostic Repeater to report inaccurate distance measurements?

Inaccurate distance calculations occur if the cable type is misconfigured (velocity factor), if spur lines exist on the segment, or if non-standard cable lengths were used during topology determination.