Hello Shailaja,

Some of the books required for different subjects in instrumentation branch for gate preparation are as follows:

Mathematics-  Advanced Engineering Mathematics by Erwin KreyszigGate, Engineering Mathematics by MADE EASY.

Network Theory- Engineering Circuit Analysis by Steven M. Durbin, Jack E. Kemmerly , William H. Hayt

Analog Electronics- Fundamentals of Microelectronics by BEHZAD RAZAVI

Digital Electronics- Solved previous year questions from EC and IN streams

Signals and Systems- Signals And Systems (Schaum’s Outline Series) by H P HSU Signals & Systems by Alan V. Oppenheim

Communication Systems- Modern Digital and Analog Communication System by B P LATHI

Electrical and Electronic Measurements- A Course In Electrical And Electronic Measurements And Instrumentation by A K SAWHNEY

Bequett

Control System- Automatic Control Systems by B C KUO

Process Control- Process Control: Modeling, Design, And Simulation by B. Wayne Bequette

Transducers- Introduction to Measurements and Instrumentation by ARUN KUMAR

GATE 2018 Enstrumentation Engineering

Good luck!