Suresh T,
There is a KnowledgeBase here on ni.com that goes into great detail about programmatic slot and device number detection. You can find that device by following this link:
Programmatic PXI Slot DetectionPlease read over that document (and the related links at the bottom of the page if they apply) and see if that is able to clarify your issue. If that solves your issue, then great. However, if you still have questions after reading over the KnowledgeBase, please make another post with some additional questions, so that this forum can assist you in resolving your issue.
Best of luck with your application.
Regards,
Jed R.
Applications Engineer
National Instruments