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Tag Archives: sampling
Coning and Quartering
For a heterogeneous material consisting of large particulates, the original (or gross) sample may be too large to analyze. For example, a Ni-bearing ore with an average particle size of 5 mm may require a sample weighing one ton to … Continue reading
Sample Thief
A sample thief is used for sampling smaller particulate materials, such as powders. A typical sample thief consists of two tubes that are nestled together. Each tube has one or more slots aligned down the sample thief’s length. Before inserting … Continue reading
Riffle Sampler
For particulate materials, particle size often determines the sampling method. Larger particulate solids, such as ores, are sampled using a riffle, which is a trough containing an even number of compartments. Because adjoining compartments empty onto opposite sides of the riffle, … Continue reading
Gravity Corer
This figure shows a schematic diagram of a gravity corer in operation. The corer’s weight is sufficient to penetrate into the sediment to a depth of approximately 2 m. Flexible metal leaves on the bottom of the corer are pushed … Continue reading
Systematic-Judgmental Sampling
This figure shows a systematic–judgmental sampling plan for monitoring the leaching of pollutants from a landfill. The sampling sites, shown as red dots (•), are on a systematic grid that straddles the direction of the groundwater’s flow. Sampling along the … Continue reading
Nyquist Theorem: Why Sampling Frequency Matters
According to the Nyquist theorem, to accurately determine a periodic signal’s true frequency, we must sample the signal at least twice during each cycle or period. If we collect samples at an interval of Δt, the highest frequency we can … Continue reading
Importance of Sampling to Overall Uncertainty in an Analysis
The overall variance in an analysis, s2, is the sum of the variances arising from the method, (smeth)2, and the variance due to sampling, (ssamp)2. s2 = (smeth)2 + (ssamp)2 The blue curve in this figure shows the method’s contribution to the … Continue reading