Wednesday, July 21, 2021

Yarn sampling method

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Yarn sampling method:

The yarn gets available in different package forms. The selection of a small number of such packages from a large number is a big problem. The yarn may be in the form of ring bobbins, a skip of mule cops, a bundle of hanks and cheeses or cone forms. Random sampling is preferred. Great care is taken for mill experiments and research to ensure that this kind of sample is obtained. Niceties of randomisation by means of packs of cards and tables of random numbers are sacrificed in the interest of speed and economy of effort. It must not be inferred that routine mill samples are therefore biased. The randomisation is merely less refined than in the research work. 

Use of random numbers table:

Suppose that 50 ring bobbins are available for testing. We have to select the 10 bobbins for testing. A serial number is given to each bobbin or all the bobbins are placed over the table. These bobbins are arranged in five rows. Each row of bobbins has 10 bobbins. Now the bobbins are selected from the bulk according to the random sampling number table.

We start to read numbers in pairs from anywhere in the above table. Suppose that we start reading from row number two. The first number of this row is 74. 74 is greater than 50 so that we ignore it. Next comes 49. First of all, we select bobbin no 49 from the bulk. The next number is 04 that is less than 50. Therefore bobbin no. 04 will be selected. We keep the reading of the table continuously and select the bobbins accordingly. If a number is more than fifty, it is ignored and the next number is considered. The selected bobbin numbers for the given bulk will be as below:
49, 04, 03, 10, 33, 11, 48, 38, 31,23.
The numbers getting already selected are also ignored while you select the next number.

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