![]() Experienced scientists typically shun using a single number answer to the question “What size are those particles?”, and prefer to include a way to define the width. ![]() Most instruments are used to measure the particle size distribution, implying an interest in the width or breadth of the distribution. The mean value is flanked by 1 and 2 standard deviation points. For the denominator take the geometric D i to the third power multiplied by the percent in that channel, summed over all channels.įigure 3: A normal distribution. For the numerator take the geometric D i to the fourth power multiplied by the percent in that channel, summed over all channels. The D i value for each channel is the geometric mean, the square root of upper x lower diameters. The best way to think about this calculation is to think of a histogram table showing the upper and lower limits of n size channels along with the percent within this channel. The equation for defining the volume mean is shown below. Laser diffraction results are reported on a volume basis, so the volume mean can be used to define the central point although the median is more frequently used than the mean when using this technique. 3) for an explanation of number, surface, and volume distributions. There are multiple definitions for mean because the mean value is associated with the basis of the distribution calculation (number, surface, volume). The various mean calculations are defined in several standard documents (ref.1,2). Mean is a calculated value similar to the concept of average. Figure 1: Symmetric distribution where mean=median=mode
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