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LA-960 Gauge Repeatability and Reproducibility Study

A study on LA-960 gauge-to-gauge variation was performed with 40 unique, randomly selected units of the LA-960 Particle Size Analyzer: 20 for wet measurements and 20 for dry.

Materials and Methods

Two NIST-traceable, polydisperse (range of sizes) glass bead materials were used in this study. The challenge samples were PS-202 (3-30 µm) and PS-215 (10-100 µm) from Whitehouse Scientific. PS-202 was measured in an aqueous wet dispersion according to the method outlined in Analytical Test Method 112. PS-215 was measured in a dry dispersion using the PowderJet accessory according to the method outlined in Analytical Test Method 113. The raw scattering data was transformed into a particle size distribution via the Mie scattering theory.

Results

Overlay of 20 PS-202 Particle Size Distribution Results

Overlay of 20 PS-215 Particle Size Distribution Results

D10, D50, D90 results with Coefficient of Variation for 20 unique PS-202 wet measurements

D10, D50, D90 results with Coefficient of Variation for 20 unique PS-215 dry measurements

Analysis

ISO 13320:2009 section 6.4 states that for the median size of the distribution the coefficient of variation should be less than 3%. Values at side of the distribution such as D10, D90, should have a coefficient of variation not exceeding 5%. PS-202 (3-30 µm) and PS-215 (10-100 µm) were tested with 20 units each. The coefficient of variance is 4.03%, 2.40% and 2.79% at D10, D50 and D90 for PS202, and 2.35%, 2.95% and 4.60% for PS215. All the results meet ISO 13320:2009 specification.

Variability gauge study for PS-202

Variability gauge study for PS-215

Variability gauge summary for PS-202

Variability gauge study for PS-215

Conclusions

This study aimed to mimic real-world conditions for many customers who must reconcile results from multiple operators, units, and locations. This is particularly important for those users with units across the world where the challenge of supporting across multiple time zones and languages grows quickly. In this context the LA-960 Particle Size Analyzer proves an excellent solution with superb data correlation for realistic (polydisperse) samples across:

40 randomly selected units
2 locations
6 operators
and acquired over 2 years (i.e. no drift)

This is accomplished without any unit-matching technique and at normal performance (i.e. no low sensitivity data processing). Such performance is unmatched on the market today.

Precision Definitions

The word precision is often used as a catch-all to describe the results from any kind of repeated test. Understanding the different types of precision is important because some tests are more difficult (and meaningful) than others.

Repeatability - Measurement variation with a single operator and single instrument on the same sample, over a short amount of time with all other variables held constant (i.e. location). Think of this as taking a sampling, loading it into the LA-960, and taking three consecutive measurements without draining.

Reproducibility - Measurement variation with either multiple operators on multiple instruments on the same sample (but possibly multiple lots) in multiple locations. Not all of these conditions must be satisfied. This is a much more taxing test than repeatability and is the test performed for this study. When a manufacturer makes a claim about precision, make sure to know which type.

Intermediate Precision - Measurement variation with multiple operators on either single or multiple instruments, in the same location across multiple days.

The table below helpfully summarizes how these three tests differ. This information appears courtesy of ASTM and can be found in ASTM E177, Practice for Use of the Terms Precision and Bias in ASTM Test Methods, and E456, Terminology Relating to Quality and Statistics.

	Repeatability Condition	Intermediate Precision Condition	Reproducibility Condition
Laboratory	Same	Same	Different
Operator	Same	Different	Different
Apparatus	Same	Same *	Different
Time between Tests	Short **	Multiple Days	Not Specified

* This situation can be different instruments meeting the same design requirement.
** Standard test method dependent, typically does not exceed one day.