Accuracy and Precision of Microtrac Particle Size Analyzers
Philip E. Plantz, PhD
Application Note
SL-AN-06 RevA
Provided By:
Microtrac, Inc.
Particle Size Measuring Instrumentation
Introduction
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Accuracy and precision have distinct meanings. Generally, accuracy refers to the ability of an analytical device to
provide a measurement that is within a defined error from an established, true, and verifiable value. Precision is a measure of the recurrence of a value whether it is accurate or not. Two types of precision can be described: repeatability and
reproducibility. In terms of particle size measurement, repeatability refers to the ability of an instrument to repeat its own measurement while the same sample resides in the circulating system. Reproducibility, on the other hand, is related to the comparison of two or more instruments in which reprentative (repeatable sampling assumed) samples are introduced to each of the instruments. Repeatability is statistically more variation-free than reproducibility becau a single instrument measures the same recirculating sample when fluid suspended particles are measured.
Accuracy
Accuracy is a concept that is difficult to define for particle size measurement of irregularly shaped particles. For a
sphere, one can easily define its surface and diameter using the radius of the particle and the basics of geometry. If 100% of the particles are spherical and are the same size, an instrument can be designed to measure that size. Since probably 99% of the industrial particles measured are not spherical (they are usually very irregularly shaped), one cannot u simple
geometry to define the size since many dimensions will exist for each particle. This situation is made more complex since while most powder process produce reproducible particle size distributions , they usually do not produce particles of exactly the same shape and size. Since there are billions upon billions of particles being produced in a process, it is very difficult, if not impossible, to accurately determine the size of each acicular particle in a distribution with 100% accuracy. The irregular particle shapes and the fact that shape has a different effect on each measurement method also contribute
The provide poorer quality
and process control
The provide good quality
and process control Figure 1. Diagram showing the possible combinations of accuracy and precision.
Good precision is necessary to controlling quality or processing.
to variations among the data reports by various instruments and methods. Fortunately, methods that have a strong scientific foundation can be correlated, meaning that although the data do not entirely agree, there is a mathematical relationship
between them that allows conversion from one data report to another. We have found in our 35-year history that Microtrac® data demonstrate a regression that is linear with other methods such as sieves, counters, and surface area with correlation coefficients as high as 0.9999. Thus, while it is difficult to define the accuracy of measuring the size of a non-spherical particle, the data are quite valid and usable.
It is also valuable to note that Microtrac1 instruments are designed according to first-principle physics, meaning that instrument design is bad upon pure forms of optics that dictate the location of the lar, lens, cell, detector, etc. Thus, calibration is not necessary. However, it is advisable to measure test materials on a prescribed basis to assure that the instrument is operating properly. The materials are available from Microtrac Inc in the form of Microtrac Reference Materials. The testing then becomes performance testing rather than calibration.
Precision
Usually, important to customers are reproducibility and repeatability of measurements and the ability of instru-mentation to respond to product not meeting documented specifications. The measurement aspects depend upon, in part, the stability of the instrument as well as its integrity and design robustness. Repeatability in this context means the ability of the instrumental method to obtain the same answer for the same sample of material. Such robust measurements allow a process to be controlled. Data consistency allows operators and process engineers to make confident, informed decisions on the proper action to take in respon to any non-conforming process issues. Actions in respon to data promote the quality of the product and permit decisions as to whether the product is good or bad, or within particle size specification or not. To achieve this l
evel of confidence, Statistical Process Control approaches may be ud and are, in fact, performed successfully by Microtrac customers.
Repeatability will vary depending upon the challenge placed on the instrument, and most light-scattering instrument manufacturers u very narrow, mostly spherical particles to provide an answer. Since we already know that such materials are the exception rather than the rule, the accuracy and repeatability statements may not fully address the repeatability question. Thus, broader, non-spherical distributions may give a better indication of repeatability. The data supplied reprents the measurement of "spherical" and non-spherical particles.
While at first thought, one might consider the above discussion unusual in that accuracy cannot be defined except under very narrow, rigorous conditions of shape and distribution, it is quite similar to the notion of accuracy for some other types of analytical instruments. One such measurement is VISCOSITY. There are veral methods by which viscosity can be measured, and the resulting data may be different. Depending upon the concentration of solids, temperature, and prence of other materials in the slurry, the viscosity values will vary among methods. For this reason, conditions of temperature and shear forces applied are important to report as part of the measurement. Thus, there is not an accuracy statement for viscosity, but the data are nevertheless uful if they are repe
atable and consistent.
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While Microtrac considers integrity our highest order of business, we offer the data below to demonstrate repeatability (actually reproducibility) of all aspects of instrument manufacturing where data variations are a result of the combination of operator variations, sampling opportunity variations, sample preparation variations, normal instrumental variations (data for at least 20 instruments are ud), circulating systems variations, and materials variations. As explained above, repeatability can be expected to show less variation. As the reader will note, a variety of materials and sizes are employed for proper and full testing of each Microtrac model. The materials shown reprent only a portion of the materials ud in our manufacturing operations. In addition, note that becau the reproducibility information includes all possible variations, the percent variation reprents a worst-ca situation.
男士快速美白Typical Instrument-to-Instrument Reproducibility of Installed Microtrac
Instruments
S3500 and S3000 Particle Size Analyzers – Minimum 20 instruments included
童话英文版歌词Microtrac Model Material Parameter Value Instrument
to
Instrument
Variation Within
Instrument Precision
S3000 / S3500 Water Dispersion 650 µ. Spherical
Glass II
50%* 648 0.9% 0.7
%
S3000 / S3500 Water Dispersion 0.102 ± 0.003 µ.
polystyrene
50% 107 4% 0.6%
* 50% is the median diameter of the volume distribution 1®Microtrac is a U.S. registered trademark of Microtrac, Inc.
Microtrac Nanotrac and UPA 150 Particle Size Analyzer with Certified 0.460µ Polystyrene- Minimum 20
instruments included
Microtrac Model Material Parameter Value Instrument
to
Instrumentpower struggle>绯闻女孩第四季
Variation Within
Instrument
Precision
UPA 150 / Nanotrac 150 Certified
Polystyrene
0.460 ± 0.007 µ.
50% 0.481 1.2% 1.1%
Microtrac X100 Particle Size Analyzer with Certified Glass, BCR 66, and Certified 0.460µ
Polystyrene - Minimum 20 instruments included
Microtrac Model Material Parameter Value Instrument
to
Instrument
Variation Within
Instrument Precision
Microtrac X100 0.04-704 µCertified Glass
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20.3±1.4µ.
50%* 21.10 0.02% 0.018%
volarMicrotrac X100
0.04-704 µ
BCR 66 50% 1.12 1.12% 1%
Microtrac X100 0.04-704 µ
英语在现翻译Certified
Polystyrene
0.460 ± 0.007 µ
50% 0.431 1.2% 0.9%
®Microtrac is a U.S. registered trademark of Microtrac, Inc.
Microtrac instruments are manufactured under rigorous manufacturing specifications to assure reproducible measurements from instrument to instrument and repeatable measurements on the same sample. Components are carefully lected or designed to assure robust, long instrument life with little maintenance. Engineering departments, rvice personnel, production/manufacturing personnel and applications laboratory combine as a team to design and manufacture best quality particle size instrumentation that requires little operator training while providing support for advanced particle measurement applications.
