Introduction
As a general rule, instruments available on the market give quick results. However, the type of instrument used, the system accuracy, and the measurement protocol can affect the reproducibility of the measurement. The ISO 13320-part1 standard has been developed in order to provide the user with results that are independent of the instrument used.

The ISO 13320 Standard
The standard requires that the manufacturer calibrate the instrument using Certified Reference Materials (CRMs) of a known size distribution. The user must also verify operation of the instrument, both repeatability and accuracy, at regular time intervals using CRMs. The main requirements of the standard are the following :

Table 1: Summary of the main requirements of the ISO 13320 standard.

Requirement	Target values	Test Method
Repeatability (6.4 in the standard)	Coefficient of variation <3% for X50 <5% for X10 & X90 (below 10µm, these values should be doubled)	The measurement is done on at least 5 different samples from the same batch
Accuracy (6.5 in the standard)	Maximum deviation from the certified range : <3% for X50 <5% for X10 & X90 (below 10µm, these values should be doubled)	Mean value over 3 independent measurements

Note: X50 represents the median diameter in mm, which means 50% (by volume) of the particles are smaller than this diameter.

The ISO13320-1 norm can be downloaded on the ISO web site : click here

Available CRM
Certified Reference Materials (CRMs) are made of spherical particles and the size distribution of these particles must retraced to a recognised size standard.

 

 

Fig 1. SEM Picture of Certified Glass Beads (from Whitehouse Scientific)

 

Measurement of the CRM with a CILAS Analyzers
Data collected using the CILAS 930L,1064L and 1180L instruments showed better repeatability and accuracy values than required in the ISO 13320 standard. Statistics from over 50 production instruments have shown a reproducibility of better than 1%.

Fig 3. Measurement of the 10-100 m m CRM with a CILAS 1064 system

CILAS instruments are very accurate because of their unique short bench design. All CILAS systems use a permanently aligned optical bench without any moving parts to provide superior repeatability.

The ISO 13320 standard provides the industrial laboratory an effective method for instrument selection. Laboratories who use the standard can guarantee the accuracy and reproducibility of their measurements throughout the entire life of the instrument.