Ramesh,
I think you have got enough replies from the experts to solve your query.
As you said, you want to generate multiple Maintenance plan calls at a time but for a particular plan only one call should be raised in this case I would summarize all the answers above as:
1. Use common sort field in all the maintenance plans.
2. in (manual)IP30 use the sort field and generate the calls in once and whenver you need to raise a call.
And also, I would add one more option here i.e.,
3. Tick the field "Completion Requirement" in "Maintenance plan scheduling parameters" tab just in case the system would not create new order/ notification if one is already open.
Hope this solves your query.
Please provide the feedback.
Chin2.