Task Configuration Recommendations for HA System

For a better performance of the HA system please consider the following recommendations in your project task configuration:

• Use the real time priorities for all HA related tasks
• Use the cycle times based on the formula (see the following table)
• If the tasks have a same cycle time (e.g. HA and Modbus task) merge those tasks
• If local I/O modules or coupler modules are used, consider their bus cycle options
• Measure PLC and PLC load during operation. If the PLC load is higher than 60 % try the following steps (Note: watchdog stops the PLC at 80 %):
  • Increase HA cycle time (e.g. to 8 ms / 12 ms / 24 ms, …) and all others according to above formulas
  • After each step check PLC load (must be < 60 %) and PLC load (must be < 80%)
  • Use a more performant PLC type

Task	Priority	Cycle Time
HA	10 (high)	4 ms or higher (based on PLC load)
Modbus	11 (medium)	Same as HA or (3 ms + roundup (3 ms + (#CI modules/2))
Application	12 (low)	HA cycle time * max. (3 ms, roundup (3 syncdataBytes/1400))