PLC Utilization

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  • cpuload: This value represents the time the PLC requires to calculate all processes running on the PLC. For a good system performance this value should be less than 80%. In case of a higher value, the degree of utilization should be reduced by using a more powerful PLC or by reducing the amount of processes.
  • plcload: This value represents the time the PLC requires to calculate all real time processes. Real time processes are either high priority system tasks or IEC tasks with a priority between 0 and 15. For a good system performance this value should be less than 60%. In case of a higher value, the degree of utilization should be reduced by using a more powerful PLC. If the value reaches 80% the PLC stops with an exception.

During commissioning we recommend to monitor the CPU and PLC values online with one of the following methods:

Automation_Builder

Commissioning via PLC shell: PLC Shell Commands

Automation_Builder

Commissioning via Device Trace for cpuload and plcload. In order to display the load of the CPU or PLC, proceed as follows:

  1. In the device tree, right-click the PLC_AC500 <…> node. Click Add object and select Device Trace.

  2. Rename the new node, e.g. “CPU_Load” and double-click to open the trace view.

  3. Right-click in the view and select Upload Trace.

  4. In the upcoming dialog click Upload to load the data into the view. Configure the trace view for plcload in the same way.

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IEC Applications/IEC program

To access the parameters plcload and cpuload please use system functions as follows:

  • plcload: SchedGetProcessorLoad() included in library ‘CmpSchedule’
  • cpuload: SysMCGetLoad() included in library ‘SysCpuMultiCore’.