Eyepiece Graticules

Particle Sizing and Distribution

The use of the eyepiece graticules shown in the following section make it possible to analyze specimens containing particles as an alternative, or in addition to, sieving. Graticules for particle size analysis are particularly popular when there are only limited quantities of particles or where particles are smaller than 50 micron diameter. The basic principle is to compare the particles to the globes and circles of varying sizes that appear on the graticule - dark particles being compared to solid globes, and light or transparent ones to the circles. Naturally the procedure varies with the graticule concerned.

• Patterson Globes & Circles - NG1

• Porton  NG2

• New Porton - NG12

• British Standard Graticules - NG10

• Fairs - NG5

• Particle Analysis Test Slide - SG7

Patterson Globes and Circles - NG1

The graticule consists of a central rectangle, sub-divided into nine smaller rectangles with a number of increasing circles outside the top and bottom horizontal edges, The marked figures are the diameters of the circles in units, 250 units represent the horizontal length of the large rectangle. Rectangle size is 4.5 mm x 2.025 mm. Circle sizes in microns are: 450, 360, 270, 225, 180, 145, 110, 74, 37, and 18.

NG1 Patterson Globes and circles. Surface chrome image

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Porton NG2

The circle areas of the Porton graticules increase with Root 2 progression as do the division on the right hand side of the rectangle. These divisions are numbered for convenience. Rectangle size is 4.5mm x 2.25mm. Circle sizes in microns are 560, 400, 280, 200, 140, 100, 70, 50, and 35. The specimen is racked on the mechanical stage of the microscope and traverses are taken right across the deposit sizing all the particles encountered

NG2 Original Porton Globes /circles. Surface chrome image

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New Porton - NG12

The NG12 graticule is particularly useful since the array of globes and circles are conveniently close to where the particles pass. At the end of each band of the sample the mechanical stage is traversed vertically to take in the next band until the whole sample has been covered.

NG12 Modified Porton patterns globes and circles Surface chrome image
 

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British Standard Graticules - NG10

In this graticule the circle areas double progressively, hence the diameters alter by Root 2, so that the size classes can form a continuation of the standard series of sieves for particle sizing, Each particle is assigned to a size class defined by two adjacent circles which represent the size limits of that class. Thus the distribution of size is obtained in terms of the diameter of circles having the same projected area as the particles. This method will cover particles in the range 150 micron to 0.38 micron. The size distributions with respect to their number and weight are determined separately. Final results are calculated as cumulative percents. Originally designed by the National Coal Board for use in coal mining.

NG10 British Standard (BS3625/BS3260) Globes & Circles. Surface chrome image.
 

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Fairs - NG5

Designed to extend the sizing range of globe and circle graticules. Example: Used in conjunction with NG2 the overall size range=128:1. The circles increase by 2.
Note: Both graticules would have to be used with the same microscope, eyepiece and objective.

NG5 Fairs, Grid length 4 mm, Glass sandwich.
 

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Particle Analysis Test Slide - SG7

Ideal for staff training, this has 100 particles of various shapes and sizes. Each shape is numbered. Designed for comparing various shapes and sizes, and as a means for logging and communicating this information.

SG7 Test slide for particle sizing. Surface chrome image.

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