18000

Check PLC Status

Navigate to Diagnostics > PLC > Status to verify PLC CPU state and check for STOP condition in STEP 7 or TIA Portal.

Look for red STOP LED on PLC CPU module as quick visual confirmation

Review PLC Diagnostics Buffer

Access PLC diagnostics buffer via HMI menu Diagnostics > PLC > Diagnostics Buffer to identify specific runtime error codes.

Document all error entries before clearing buffer for service analysis

Analyze Program Logic

Connect with STEP 7/TIA Portal to examine PLC program at fault location, check for array bounds violations, division by zero, or invalid pointer access.

Use online monitoring to trace program execution path leading to error

Correct and Download Program

Fix identified program error, compile, and download corrected program to PLC, then switch CPU to RUN mode.

Ensure machine is in safe state before switching PLC to RUN mode

Check Hardware Status LEDs

Inspect all PLC rack modules for red FAULT LEDs, particularly CPU, power supply, and communication modules.

Flashing red LED patterns indicate specific fault types - consult module manual for LED code interpretation

Verify Power Supply Status

Check PLC power supply module status LEDs and measure 24VDC output voltage at terminals, ensure voltage is within 22-28VDC range.

Use proper lockout/tagout procedures when measuring voltages

Access Hardware Diagnostics

Use HMI Diagnostics > PLC > Hardware or STEP 7 Hardware Diagnostics to identify failed modules and specific fault codes.

Hardware diagnostics will show module status even when CPU is in STOP state

Replace Faulty Hardware

Replace identified faulty PLC modules, ensuring proper module insertion and secure connector seating before powering up.

Power down entire PLC rack before replacing any modules to prevent damage

Check Communication Interface

Verify NCK-PLC communication interface status in Diagnostics > NCK > Communication, look for active connection status.

Green communication LEDs on both NCK and PLC sides should be solid, not flashing

Inspect Communication Cables

Check MPI/PROFIBUS/Ethernet cables between NCK and PLC for physical damage, proper connection, and termination resistors.

Do not disconnect communication cables while system is powered to avoid data corruption

Verify Interface Configuration

Check NCK parameter MD10350 (PLC_INTERFACE) and corresponding PLC communication settings match for protocol, baud rate, and addressing.

Use SINUMERIK parameter interface to verify MD10350 matches PLC hardware configuration

Reset Communication Interface

Perform communication reset via Service > NCK > Reset Communication or power cycle both NCK and PLC systems simultaneously.

Coordinate with production before performing system reset as it will interrupt all operations

Check Cycle Time Monitoring

Access PLC CPU properties in STEP 7/TIA Portal to review cycle time monitoring settings and current/maximum cycle times.

Typical SINUMERIK PLC cycle times should be under 50ms for optimal NCK coordination

Analyze Program Performance

Use online program monitoring to identify program blocks with excessive execution times, particularly complex mathematical operations or loops.

Long cycle times can cause NCK synchronization issues even before PLC enters STOP state

Optimize Program Logic

Restructure time-critical program sections, implement program segmentation, or move complex calculations to interrupt routines.

Use PLC program profiling tools to identify bottlenecks in execution time

Adjust Cycle Time Limits

If necessary, increase PLC cycle time monitoring limits in CPU configuration, but ensure NCK coordination requirements are maintained.

Increasing cycle time limits may affect real-time machine response and safety functions

Verify Memory Status

Check PLC CPU memory utilization in STEP 7/TIA Portal CPU properties, ensure sufficient work memory and load memory available.

SINUMERIK PLC applications typically require 30-50% memory headroom for stable operation

Compare Configuration

Verify downloaded PLC configuration matches hardware configuration using Hardware Configuration comparison tools.

Configuration mismatches can cause intermittent faults that are difficult to diagnose

Perform Memory Reset

Execute PLC memory reset (MRES) using CPU mode selector or STEP 7 function, then reload complete program and configuration.

Memory reset will erase all PLC program and data - ensure backup is available before proceeding

Reload System Software

If memory issues persist, reload PLC operating system and SINUMERIK PLC basic program from original installation media.

Keep original SINUMERIK installation files readily available for system recovery procedures