I am trying to count the number of bars created in a subgraph in Sierrachart. For example, how many 2000 volume bars are created within 30 mins duration. Is there any study to achieve that. If anyone knows please let me know.

You can do it with the Spreadsheet Study study.

Put this in K3:
=MATCH(A3-30/1440,A3:A1002,-1)

This works for any bar type whose duration is <=30 minutes, and it includes the current bar.

To exclude the current bar, use this:
=MATCH(A3-30/1440,A3:A1002,-1)-1