What is SI unit?
International system of unit (SI) is world’s most used system of measurement.
International system of unit (abbreviated SI) is used officially in all countries except USA,Myanmar and Liberia.
It has seven basic units,from which all other units are derived.
Length - Meter
Mass - Kilogram
Time - Second
Electric current - Ampere
Thermodynamic temperature - Kelvin
Luminous intensity - Candela
Amount of substance - Mole
Unit symbols are normal vertical letters and Quantitative symbols are inclined italic letters.All formulas indicating quantities must be written with italic letters.
All other units are derived from base units. There are 22 derived units.
In instrumentation we use only 2 base units level and temperature and two derived units flow and pressure.
Measurement is comparison between the value of process quantity and its unit.
The main advantage of SI system compared to imperial system is that bigger units are obtained from base units by multiples of ten and smaller units by sub multiples of ten.
For example 1 ton = 1 kg * 1000 (Bigger unit)
1 gram = 1 kg / 1000 (Smaller unit)