Graticules, Stage Micrometers, and Calibration Standards


Eyepiece Graticules (continued) E. Asbestos Fiber Analysis


Walton and Beckett Graticule for Asbestos — G22, G24, G25


Calibration factors are required for each of these graticules. See note below.


G22


The Walton and Beckett graticule is used for counting fibrous dust (e.g. asbestos or glass fibers) and is particularly useful where the majority of fibers to be counted are shorter than 5 microns. The circle is divided into four by two diametrical lines scaled in units of 5 and 3 microns respectively. 3 and 5 microns are the critical measurements of fiber lengths and diameters used in fiber counting. Unlike the usual globes of other particle graticules, the Walton and Beckett have a series of shapes to compare objects with. These shapes have been designed for comparison with fibers, especially since they incorporate an aspect ratio of 3:1 or 5:1 essential for such analysis.


IMPORTANT NOTE: The circle on these Walton & Beckett graticules must represent 100 microns at the stage and each one must be manufactured to suit the individual instrument.


G24


Therefore, details should be provided with your order of: 1. Calibration factor, if known; 2. Objective magnification; 3. Eyepiece magnification; 4. Diameter of graticule disc required; 5. Microscope make and model.


Pattern G22


G24 G25 G25 Description Dia.


Walton & Beckett for asbestos. 3:1 ratio. 16mm Glass sandwich.


19mm 21mm


Walton & Beckett for asbestos. 5:1 ratio. 16mm Glass sandwich.


19mm 21mm


Based on the G22, the G25 is produced by 16mm the Institute of Occupational Health (1996). 19mm Glass sandwich.


21mm


Walton & Beckett G22


Cat.#


68028-16 68028-19 68028-21 68029-16 68029-19 68029-21 68030-16 68030-19 68030-21


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