Control systems is the root of lots of scientific fields and technical disciplines. We can say it is divided in:
- classic control systems
- digital systems
- Discrete control
- Artificial Intelligence techs
Classic control systems and digital control are mainly restricted to academic means as they rely on a deep analysis of the problem. Discrete control does not rely on closed Loops, and we can say that PLCs, microcontrollers are the devices used here. AI techs also are mainly used in academic means, however you can see that most Robots these days use one of its fields. Instrumentation and automation is simply a pragmatic view of control systems: eliminate most of the math, make the physics of it standard. In this sense, the Automation and instrumentation engineer does not need to get in touch with the technology it self, he just uses tools like PLCs, network bridges and transmitters.
So automation and instrumentation engineers won't deal directly with microprocessors or A/D converters. It is not an easy task but it demands a lot of pratical work.
It helps if you are programming Allen Bradley or Siemens PLCs, because these guys are standard makers of PLCs and they allow a huge variety of devices.