Instrumentation

Instrumentation is the science of measuring and controlling variables. Variables are anything that can affect or change other things. Instrumentation can be used to make processes faster or more efficient, meaning they use less effort, energy or money to produce the same results.
The word instrumentation may also mean the machines made to measure and control things.
The science of instrumentation involves figuring out the best way to measure or control something, building the machine or tools, and checking if the results are good and true. It may also include setting up and using the machine or tools.
Variables.
An instrument is a tool used to measure and control the variables that affect a process. Here are some variables that people use instrumentation to measure and control:
Instruments.
Two examples of instruments are valves and flame detectors. A valve is a controlling instrument that controls the flow of fluids, which can be gases, liquids, or other fluids. A flame detector is a measurement instrument that detects a flame by analyzing the light. 
Instrumentation engineering.
The engineering behind instrumentation deals with mechanics and use of measuring instruments. Instrumentation engineers usually work in industries with automated processes. For example, chemical and manufacturing plants often have robots and other machines doing a lot of the work. Instrumentation engineers try to make things more safe, productive and stable. They sometimes use computers.