To evaluate the particle size distribution of tablet granules by sieve method. 

The unit of particle size used most frequently in Micromeritics is micrometer (μm), also called as micron (μ).
Physical, chemical and pharmacological properties of a drug depend on particle size and hence surface area of particle.
Impact of Particle size
Surface area: Particle size is inversely proportional to surface area, ie. Decrease in particle size increases surface area. Increased Surface area enhances therapeutic effect of antacid suspensions.
Rate of solution: Decrease in particle size increases effective surface area which in turn increases rate of solution.
Bioavailability: Decrease in particle size increases bioavailability by improving solubility of drug.
Mixedness: Particle size of powders in a narrow size range provides better mixedness in mixing operation.
Stability of emulsion and suspensions: fine particles with narrow particle size range produced more stable emulsions and suspensions.
Size separation: It is a process of separation of mixture in to various fractions on the basis of particle size range.
Methods of Size separation:
Sieving
Sedimentation
Elutriation
Cyclone separator
Sieving method:
This method uses a series of standard sieves calibrated by the National Bureau of Standards
Sieve shaker machine
Principle: the powdered drug is separated according its particle size using a number of sieves in a nest which are then agitated for rapid size separation.
Construction: Standard sieves of different mesh numbers are fixed in a mechanical shaker apparatus with coarsest sieve at the top & finest sieve in the bottom.
Working: A powder sample ( 50 g) is placed on top sieve in a sieve set. This sieve nest is fixed to mechanical shaker apparatus & shaken for a certain period of time. The powder retained on each sieve is weighed
Advantages:
Sieving method provide rapid and reproducible results.
It is simple and inexpensive method.
Disadvantages:
It is useful for dry solids only.
size reduction of test material may take place due to vibration of sieve shaker which introduces error in estimation.
Disadvantages:
If powder is not dry , apertures get clogged
Lower limit of particle size is 50 μm
During shaking , attrition occurs causing size reduction of particles. This results in error in estimation.