Please specify the name of the college you want admission so that I can give you more accurate details. Although the cutoffs of instrumental engineering are very low as compared to other branches but you told that you have got 50% in 12 standard which could be a problem as most of the colleges and universities have their eligibility criteria as the student should have a minimum of 65% in board exam(for general category)

About which college you want to know? In my college to get admission ,you have to crack JEE mains and from JOSA u will get seat in instrumentation engineering.