Representative process sampling for reliable data analysis—a tutorial

Abstract

Process sampling of moving streams of particulate matter, fluids and slurries (over time or space) or stationary one-dimensional (1-D) lots is often carried out according to existing tradition or protocol not taking the theory of sampling (TOS) into account. In many situations, sampling errors (sampling variances) can be reduced greatly however, and sampling biases can be eliminated completely, by respecting a simple set of rules and guidelines provided by TOS. A systematic approach for description of process heterogeneity furnishes in-depth knowledge about the specific variability of any 1-D lot. The variogram and its derived auxiliary functions together with a set of error generating functions provide critical information on:-process variation over time or space,-the number of extracted increments to composite into a final, optimal sample,-the frequency with which to extract increments-and which sampling scheme will be optimal (random, stratified random or systematic selection). In addition variography will delineate cyclic behaviors as well as long-term trends thereby ensuring that future sampling will not accidentally be performed with a sampling rate coincident with the frequency of any hidden cycle, eliminating the risk of underestimating process variation. A brief description of selected hardware for extraction of samples from 1-D lots is provided in order to illustrate the key issues to consider when installing new, or optimizing existing sampling devices and procedures. A number of practical examples illustrate the use of TOS and variography to design optimal sampling protocols for a variety of typical process situations.

Making big data smart—how to use metagenomics to understand soil quality

“…The degree of heterogeneity strongly depends on (i) the sampled compartment, e.g., the rhizosphere is less heterogeneous compared to bulk soil (Hinsinger et al 2009), (ii) the soil texture, which strongly influences aggregate formation and also nucleic acid extraction efficiency, (iii) the above ground diversity and plant coverage, (iv) season, and (v) specific site characteristics like slope, shadowing, and groundwater table. (Petersen and Esbensen 2005). Taking this heterogeneity into account, the typically 500 mg to 10 g soil used for DNA extraction often do not reflect a single microsite, but a mixture of different compartments with differing chemical, physical, and biological properties, which often makes data interpretation quite challenging and only allows a correlative analysis of microbial data with abiotic soil properties, but does not increase our mechanistic understanding of how soil ecosystems work.…”

Acoustic chemometric prediction of total solids in bioslurry: A full-scale feasibility study for on-line biogas process monitoring

“…Proper techniques for representative process sampling based on Theory of Sampling (TOS), as have been described in-depth in literatures [30,31,32] were employed.…”

“…In depth description of unbiased process sampling approaches have been previously provided in many scientific literatures [18,29,30,31,32]. In order to implement correct sampling protocol in this work, before addition of dry maize silage bioslurry in the recirculation loop was allowed to circulate a minimum five looping times and thereby well mixed.…”

“…The reference samples were used for determining the exact content of dry matter (TS) at each level. A full detailed documentation of representative process sampling on bioslurry systems, the methods of which were followed in the present study, can be found [29,31]. For each TS level, the average of each set of the dried ten increments was used as the reference sample (y) value (corresponding to TOS' prescription for a composite sample), to be used in the ensuing multivariate calibration stage.…”

“…Only Theory of Sampling, TOS [29,30,31,32], enable reliable characterisation of the heterogeneity of process materials. Typical examples of implementation of TOS in this study involved thorough mixing of the materials under study (in the loop, extracted increments, sub-samples etc.…”