Sampling Unit Variance in Discontinuous Sampling

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Questions and Answers

What is the purpose of adding a sampling unit variance correction term to equation (3)?

To account for the variance in sampling units when only some of the elements are sampled and tested (discontinuous sampling)

What is the symbol for the number of sampling units in a batch of coal?

When is a special sampling plan required?

When the sampling precision is expressed by coal quality parameters other than ash, or when the required ash precision value is less than the values listed in Table 1, or when a sampling plan has been agreed upon by the interested party.

What is the purpose of the bias test and sampling precision verification according to Appendix C?

To confirm the requirements of the sampling plan and ensure that the results are accurate and unbiased. Signup and view all the answers

What is specified in Table 1?

The total precision (ash, Ad) of sampling, preparation, and testing of coal and other coal washing. Signup and view all the answers

What is the basic sampling program based on?

A basic sampling scheme that follows the provisions of this standard. Signup and view all the answers

What is the purpose of dividing a batch of coal into multiple sampling units?

To increase the precision of sampling Signup and view all the answers

What is the minimum mass of the total sample that can be reduced to, according to Table 4?

0.01, which is equivalent to 0.2% of the ash variance due to particle characteristics Signup and view all the answers

What is the formula used to determine the number of coal sampling units?

Formula (9): M = ? Signup and view all the answers

Why may sub-samples or sub-samples need to be added during sampling?

To ensure the total mass meets the minimum requirements, thereby maintaining sampling precision Signup and view all the answers

What is the basic sampling unit amount of coal in tons (t)?

1000t Signup and view all the answers

What is the purpose of Table 4 and Table 5?

To show the minimum mass of the total sample for different types of coal samples Signup and view all the answers

What is the consequence of not meeting the minimum mass requirements during sampling?

The sampling precision is likely to decrease Signup and view all the answers

What is the formula used to calculate the number of increments when the coal sampling unit is greater than 1000t?

Formula (8): N = ? Signup and view all the answers

What is the first step in designing a sampling plan?

Developing the operating instructions based on the actual situation. Signup and view all the answers

What is the purpose of determining the sampling method?

To decide between continuous sampling or intermittent sampling. Signup and view all the answers

What are the three types of sampling modes?

System sampling, random sampling, and stratified random sampling. Signup and view all the answers

What is the importance of determining the sampling location?

To ensure that the sample is representative of the population. Signup and view all the answers

What is the purpose of determining the quality parameters?

To ensure that the measured parameters are not biased by sampling, sample preparation, and sample storage prior to testing. Signup and view all the answers

What factors affect the determination of sampling precision?

Sampling purpose, sample type, and the requirements of the parties to the contract. Signup and view all the answers

What is the importance of defining the mass of the primary increment, the post-fractionation sample, and the test sample?

To ensure that the sample is representative of the population and to avoid bias in the sample results. Signup and view all the answers

What is the purpose of outlining the elements included in all sampling plans?

To ensure that all possible problems are covered and that the sampling plan is comprehensive. Signup and view all the answers

What is the minimum increment mass, and how is it calculated?

The minimum increment mass is at least 0.5kg, and it is calculated using formula (10), where ma is the minimum increment mass in kg and d is the nominal top size of the coal sampled in mm. Signup and view all the answers

What is the purpose of Table 6 in the context of coal sampling?

Table 6 provides the minimum mass of the primary increment according to the top nominal size of the coal. Signup and view all the answers

What is increment average mass, and how is it calculated?

Increment average mass is the average mass of the increments, and it is calculated using Equation (11) when the total mass of the sample and the minimum sample weight do not reach the minimum mass specified in Tables 4 and 5. Signup and view all the answers

What are the steps involved in setting up a sampling plan for coal?

The steps involved in setting up a sampling plan for coal are: (a) determining the coal source and batch, (b) determining the parameters to be determined and the type of sample required, (c) determining the nominal top size of the coal, the minimum mass of the total sample and increments, (d) determining or assuming the required precision, (e) determining or assuming coal variability and sample preparation variance. Signup and view all the answers

What is the purpose of determining the nominal top size of the coal in the sampling plan?

The purpose of determining the nominal top size of the coal is to calculate the minimum mass of the primary increment and the total sample. Signup and view all the answers

What is the role of coal variability in the sampling plan?

Coal variability, which includes primary increment variance and sampling unit variance, is used to determine the required precision and the minimum sample size. Signup and view all the answers

What is the purpose of determining the parameters to be determined in the sampling plan?

The purpose of determining the parameters to be determined is to identify the characteristics of the coal that need to be measured or analyzed. Signup and view all the answers

What is the relationship between the minimum sample mass and the increment mass?

The minimum sample mass is the sum of the increment masses, and the increment mass is calculated using formula (10) or determined from Table 6. Signup and view all the answers

What is the purpose of determining the sampling unit variance in coal sampling?

To determine the variance in the sampling process, which affects the accuracy of the results. Signup and view all the answers

What are the two methods used to determine the sample preparation and testing variance?

Method one involves taking two samples from each of at least 20 samples, and Method two involves making analysis samples from at least 20 samples. Signup and view all the answers

What is the formula used to calculate the sample and laboratory variance in Method one?

VPT = (Σdi^2) / (2n) Signup and view all the answers

What is the initial assumption of the sample preparation and testing variance in the absence of data?

VPT = 0.2 Signup and view all the answers

What is the purpose of calculating the initial sampling units?

To determine the number of sampling units required for representative sampling. Signup and view all the answers

What is continuous sampling, and how is it used in coal sampling?

Continuous sampling is a method of sampling where samples are taken continuously from a batch of coal, and it is used to calculate the initial sampling units. Signup and view all the answers

Why is it important to determine the sample preparation and laboratory variance in coal sampling?

To assess the accuracy and reliability of the results, and to ensure that the sample is representative of the population. Signup and view all the answers

What is the significance of the number of sampling units and increments in coal sampling?

The number of sampling units and increments affects the accuracy and reliability of the results, and ensures that the sample is representative of the population. Signup and view all the answers

Study Notes

Sampling Principles

Discontinuous sampling requires a sampling unit variance correction term to be added to equation (3)
VSPT and PL calculations are performed according to equations (6) and (7)

Basic Sampling Scheme

The sampling principle is based on the provisions of this standard, and special sampling plans can be devised in certain cases
The sampling precision is expressed by the coal quality parameters other than ash
The required ash precision value is less than the values listed in Table 1
A sampling plan has been agreed upon by the interested party

Sampling Unit and Increment

The total precision (ash, Ad) of sampling, preparation, and testing of coal and other coal washing is specified in Table 1
The number of increments when the coal sampling unit is greater than 1000t is calculated according to formula (8)
The sampling unit of coal amount of more than 1000t, the number of increments is calculated according to formula (8)
A batch of coal can be used as a sampling unit, and can be divided into m sampling units according to formula (9)

Determination of Number of Coal Sampling Units

The precision of sampling is better when a batch of coal is divided into multiple sampling units
The minimum mass of the total sample is specified in Table 4 and Table 5 for general coal samples, total moisture coal samples, and particle size analysis coal samples

Sample Quality and Increment Mass

The minimum increment mass is calculated by formula (10), but at least 0.5kg
The minimum increment mass is specified in Table 6 according to the nominal top size of the coal sampled
The increment average mass is calculated according to equation (11)

Design Special Sampling Scheme

The basic procedure to set up the sampling plan includes:
- Determining the coal source, batch, and parameters to be determined
- Determining the nominal top size of the coal, the minimum mass of the total sample, and increments
- Determining or assuming the required precision and coal variability
- Determining the number of sampling units, increments, and sampling method
- Determining the sampling mode, sampling base, and location
- Determining the method of combining the increments and sampling method

Design of Sampling Procedures

The design of the sampling plan is based on the actual situation and includes the operating instructions for implementing the sampling
The operating instructions should be simple, easy to understand, feasible, and fully understood by the sampler
The type of sample is determined according to the purpose of sampling (technical evaluation, process control, quality control, or commercial purposes)
Quality parameters are determined according to the sampling purpose and the type of sample

Determining the Precision of Sampling

Sampling precision is determined according to the sampling purpose, sample type, and requirements of the parties to the contract
The sampling unit variance is determined based on a similar sampling scheme for coal
The sampling unit variance can be initially assumed to be 5 for ash content, and checked after sampling

Sample Preparation and Laboratory Variance Determination

One of the following methods can be used to determine the sample preparation and testing variance:
- Direct determination using Method 1 or Method 2
- Determination based on similar procedures for the determination of coal in similar samples
- In the absence of data, the sample preparation and testing variance can be initially assumed to be 0.2 for ash content, and checked after preparation and testing

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Description

Learn about the importance of adding a sampling unit variance correction term when using discontinuous sampling methods, and how to perform VSPT and PL calculations.