Instrumentation is a branch of engineering that specialises in Measurement and Control of variables in a system..... In Instrumentation u study Mathematics(their is a lot of it...!!!) electronics,control systems,process control,abt transducers,microprocessors and embedded systems and some topics from mechanical engineering...
If u want to know more abt wat is taught in B.tech Instrumentation Technology,den take a look at the syllabus right here "http://dspace.cusat.ac.in/jspui/bitstream/123456789/3629/1/Syllabus.PDF"
If u want to know about what jobs u will get check out this website "http://instrumentationcusat.webs.com/placements.htm"
And Yes!, u can go for M.tech in iit too, Courses include,but not limited to M.tech Robotics And Artificial intelligence,M.tech Instrumentation. U can also do Ms abroad(like Ms petrolium and natural gas)....
Hope this helps......