This article describes how an LVDT sensor works, the process measurement applications that it can be used for.
This article answers the question what is a PID controller, how do PID controllers work and what is the theory behind PID.
This article explains how a thermocouple works, the reason for thermocouple failure and how to monitor the thermocouple condition.
This technical paper will answer all your questions on what is MODBUS, how does it work, and where can I find more information.
This article provides a definition of SCADA and describes the basics of what a SCADA system is and how SCADA works.