Hi,

APL blocks must be executed in an interrupt OB, otherwise they do not work properly. 

You can use the CPU_RT block to diagnose any problems and see the actual load of the OB's->How is your CPU running. For example, if OB35 cannot be maintained, the CPU can go to emergency mode where it will reduce the cyclic time by half. So 100ms will take 200ms. This is done to prevent a CPU stop.

See the following manual: Engineering and usage of the function block CPU_RT

Common practice is to divide the blocks over multiple OB's. For example standard control like valve, motors can be used in 1 second OB, slow PID controllers can be used in 2s or slower and high speed logic such as fast PID control or digital counters can be used in 500mS or faster. 

Key Uses of the CPU_RT Block

1. Monitor CPU Cycle Load:

   • The block measures the CPU loa used by the cyclic programs (OBs) in the automation system. This helps ensure that the CPU is operating within acceptable limits.

2. Detect Performance Bottlenecks:

   • It identifies if the CPU is overloaded or if there are any delays in executing tasks within the defined cycle times.

3. Analyze Execution Times of OBs:

   • CPU_RT provides detailed data on how long each cyclicOrganization Block (OB)takes to execute, enabling optimization of program performance.

4. Generate Alarms for Critical Conditions:

   • The block can trigger alarms in case the CPU load exceeds predefined thresholds or cycle times are violated.

5. System Optimization:

   • The data collected can help engineers redistribute tasks, optimize logic, or reduce load by shifting non-critical operations to less frequent tasks.

Relation to WinCC

The CPU_RT block itself does not directly interact with WinCC, as it operates on the Automation System (AS) side. However, its diagnostic outputs can be connected to WinCC for visualization and alarm monitoring. Here's how they relate:

1. Integration with WinCC:

   • The outputs of the CPU_RT block, such as CPU load percentage, OB execution times, and alarms, can be linked to tags in WinCC.
   • These tags can be displayed on SCADA screens or used to trigger alarms in WinCC, allowing operators to monitor system performance in real-time.

2. Improving System Visualization:

   • By integrating CPU_RT outputs with WinCC, operators can visualize the performance of the automation system and take corrective actions based on system load.

3. Proactive Maintenance:

   • WinCC can generate warnings or events if the CPU load exceeds critical thresholds, ensuring proactive system maintenance and avoiding runtime issues.

Practical Use Case

• In a PCS7 system with high computational demand (e.g., large projects or complex calculations), the CPU_RT block can identify performance bottlenecks. For example:
  • If the CPU load is consistently high, the engineer can optimize the logic or split tasks across multiple CPUs.
  • The system's performance metrics can be displayed in WinCC for operators to monitor.