Re: petrochemical
Well, as i know besides the electronics used to take data, like pressure or temperature, this are the sensors, ADC, DAC and the scaling circuits, there are PLC or microcontrollers to adminiester all the control in that kind of industry, a really good example is the control used in the distillation towers, this are big towers where u separate the oil i think into the different products, like gas, butane and the different products there are from oil.
Check on the net for some of this type of control, u can use a lot of control techniques here, like fuzzy among others, look over the net for this topic, i'm sure you will find some good links.