workflows do not work

[newminder]

I created 4 workflows for one module, all set triggered by [system].
1 workflow -- condition: field b = 0 task: update field c= [option1]
2 workflow -- condition: field b greater than 0 and less than field a task: update field c= [option2]
3 workflow -- condition: field b = field a task: update field c= [option3]
4 workflow -- condition: field b greater than field a task: update field c= [option4]

testing results:
change the trigger from system to Every time a record is saved (eg. creating, modifying), works! all other triggers won't work.

ps: field b is a summary data which collect data and sum from another module (this part works well).

if anyone knows how to solve, please help share your thoughts.

[mariuszkrzaczkowski]

system - is called from PHP code, so it won't work if I didn't add proper PHP code

[newminder]

can you tell me what codes should be added in the file?