Instrumentation can be divided in two major Groups.
A ) Primary Instruments ( like pressure gauge , Pressure Transmitters , Temperature gauges and temperature Transmitters , RTDs , Thermocouples , Vibration measurement , Analysers , position transmitters , Limit switches , Level switches and transmitters ,Pressure Switches , Temperature switches , Differential Pressure Transmitters , Different type of isolating valves according to process requirement etc.
There are other primary instruments also but the list given above is most widely used in thermal power plant and any other process plant.
B) Secondary Instruments ( like recorders , printers , digital indicator , Computer , Monitor , Digital control panel , Temperature Scanner , data logger , Analogue and digital Control system , Different type of control panel of specific use like DCS , Soot Blower , Auxiliary PRDS , Drum level measurement , Turbo visory system including speed and vibration measurement . etc. Secondary instrument gets signal from primary instruments then processed and presented as per our requirement.
Instruments can also be grouped in the following manner
i) Mechanical Instruments
ii) Electrical Instruments
iii) Electronic instruments
iv) Hydraulic Instruments. ( vane control etc )
v) Pneumatic Instruments ( like Power cylinders, Control valves ,
e/p converters etc.