~ an Advanced Laboratory Imaging and Analysis System
Under proper conditions,* ALIAS provides measurements that are typically within two optical pixels (approximately 0.10 mm) of the average sample length, and within one optical pixel (approximately 0.05 mm) of the average sample diameter, of the measurements obtainable with calipers.** * - Proper Conditions:
1. Samples are large (preferably around 200 particles).
2. Particles in a given sample all have the same geometric shape (cylinder, trilobe, bilobe, quadlobe, or sphere).
3. Particles in a given sample all have approximately the same diameter (within +/- 10%) and are of the same species of catalysts. (Mixing, say, different color catalysts, can degrade ALIAS accuracy. If you have a mixed catalyst sample, Cascade Data Systems recommends you separate the particles into their various species and measure them separately.).
4. Particles are uniformly scattered on the scanner (but no closer than 1.5 inch to either the left or right edge of the scanner glass). All particles should be laid on their sides, an issue that typically arises only when measuring short particles, ones that have a chance of coming to rest on their ends.
5. No particles are touching each other.
6. Particle diameters lie within the range for which ALIAS is tuned (between 0.85 and 3.5 mm).
7. Catalyst particles also need to have fracture geometries similar to the catalysts on which ALIAS was tuned. Particles should be smooth along their long sides, but may have some jaggedness on either end. The more jagged the ends of a particle, the tougher it is to ascribe an accurate length measurement to it.
8. The Standard Error (the standard deviation divided by the square root of the number of particles in the sample) of the sample should be less than 0.10 mm for the dimension of interest.
9. The ALIAS hardware and software has been properly installed and the scanner calibration information has been properly entered.
--ALIAS is tuned for use with only a few brands and models of optical scanners, and each physical scanner needs to be specifically calibrated for use with ALIAS. Should your scanner break, do not simply buy a replacement--YOU MUST OBTAIN AN APPROVED AND CALIBRATED SCANNER directly from Cascade Data Systems. Failure to do so will cause loss of accuracy, perhaps even extreme loss of accuracy!
--The ALIAS Measurement Sytem is a system. Do not install other software on this ALIAS computer, as it may interfere with the running or performance or accuracy of ALIAS. Do not manually adjust the settings in the ALIAS.INI file. (All the changes should be done through the Options window.) Do not change any of the ALIAS files.
ALIAS was tuned using dozens of catalyst samples that are assumed to be representative of typical catalysts in use today by the oil industry. ALIAS strives to reproduce the measurements that a trained technician would achieve when measuring samples with micrometers (also know as calipers). As the diameter of particles increase, typically so does the magnitude of the difference between micrometer-measured length and ALIAS-measured length. (And also, as the diameter of the particles increase, the variability from one set of measurements done with micrometers when compared to another set of measurements done with the same micrometers also tends to increase: this is due to the particles sitting differently within the narrow jaws of the micrometers.)
** - When comparing caliper measurements and ALIAS measurements, we suggest you use the following procedure:
1. Have at least three different micrometer-trained technicians measure the same (sufficiently-large) sample with calibrated micrometers;
2. Ensure no chipping or breakage of the catalyst occurs between measurements;
3. Average the results of these three (or more) samplings together.
NOTE: It's common for caliper measurements of sample average length to differ by more than 0.10 mm from measurement to measurement, and for measurements of sample average diameter to differ by 0.05 mm. Multiple measurements are therefore required. The variation in sample average measurements when using ALIAS is typically smaller than the variation in sample average measurements when using calipers, even when particles are redistributed between successive ALIAS scans. And ALIAS sample average measurements are normally operator-independent if the proper conditions are met.
Cascade Data Systems specifies no accuracy thresholds for area, curvature and color values:
1. Area is the number of pixels each particle covers multiplied by the area of each pixel.
2. The Curvature algorithm tells, in increments of diameter, the amount by which the particle deviates from the straight and true. If a particle has a curvature of 0.33, then it differs from a straight line by an amount equal to a third of the average diameter of the particle. In layman terms what this means is that if you wanted to construct a box to hold the particle, you would have to make the box 33% wider than the average diameter of the particle in order for the particle to fit into it. Or looked at another way, the curvature value gives you an approximation of the gap that would form between the center of the particle and a tabletop if the particle curved with a nice smooth arc, and if that particle were laid on its tips so that it formed an arch. The particle in the image below has a reported curvature of 0.418, or a bounding box that needs to be 41.8% taller than the average particle diameter in order to accomodate the particle.
3. The Roundness measurement, which only applies to spheres, is the standard deviation of several diameters drawn at uniform angular increments through the center of the sphere. (The number of diameters used can be determined by counting the number of yellow diameter lines--or "double" spokes--drawn through the particle after it is scanned, highlighted and magnified in the Scan window.) The roundness of the sphere shown below was computed using eight different diameters.