Yes, I see what you mean it can be a bit confusing.
Instrumentation is a very wide field so the easiest to
explain would be to classify all the various areas in
different categories, but they are all part of the
Process measuring instrumentation, like pressure,
temperature, flow, density, level, viscosity, conductivity,
PH, redox, distance, angle ext.
Process control instrumentation, like control valve, on/off
valve, solenoids valves, valve positions, feedback positioners.
Monitoring and control instrumentation, like the DCS, SCADA,
PLC's and relay control systems.
Pneumatic instrumentation, like pneumatic valve positioners,
electromagnetic positioners, DP transmitters, level trolls,
switches and pneumatic relays and pistons.
Hydraulic instrumentation, like hydraulic control systems,
pneumatic/hydraulic solenoid valves, hydraulic control
valves, feedback positioners and pistons.
Fire and gas instrumentation, like flame, gas, smoke, heat
detectors and the addressable monitoring and control
systems. CO2, foam, 440VAC foam control valves and deluge
systems and their pneumatic and solenoid control systems
will also fall in this category.
Analytical instrumentation, like oil in water, gas
chromatographic, oxygen content, chlorine content,
florescence, dew point analyzers.
Analytical instruments are those which are used to calculate
the exact proportion in which the various constituents are
present in a substance.for eg:a gas chromatograph can be
used to calculate the exact quantities in which oxygen,
co2,nitrogen and other gases are present in air.
where as the other instruments are used to measure
the various physical quantities such as pressure,
temperature, level, flow etc in a process.
1.)Analytical instrument are laboratory type instrument whereas other instrument can be laboratory as well as plant oriented type.
2.)these are generally small in size whereas other instrument are larger in size as compared to analytical instrument.
3.) examples of analytical are cromatograph,psychrometer,spectroscopy,pH measurement etc.
whereas example of other instrument are thermocouple,thermister,orifice meter, ultrasonic flow meter etc.