buddy,instrumentation is specialized branch which deals with the measuring and operation of measuring instruments which are used in the design and configuration of automated systems.these engineers are required in heavy industries like steel plants and refineries.....
Then if u score good gate score then the central companies like IOCL,ONGC,GAIL etc require instrumentation engineers whom they recruit using gate score..but these central companies don't come to campus for recruitment,u need to attend the off campus recruitments....
Even after btech u could pursue Mtech in instrumention in NIT or IITs,The Indian Institute of Astrophysics, Koramangala, Bangalore offers integrated M.Tech.-Ph.D.(Tech) course in astronomical instrumentation in collaboration with the Department of Applied Optics and Photonics, Calcutta University. The duration of the M.Tech. course is two years.
In cusat,this year the core companies that visited the department was BP and L&T...among 15 students(without any supp) 6 of them got placed with a package of 4 lpa.......
thats all the data i got from my frd in instrumentation..hope this helps.....