【国外标准】 Standard Practice for Bias Testing a Mechanical Coal Sampling System (Withdrawn 2008)

It is intended that these procedures be used to provide an estimate of the bias of a mechanical sampling system used to collect samples of coal. Mechanical coal-sampling systems are used extensively in industry for collecting samples while coal is being conveyed or transported in various stages of production, shipment, receipt, and use. The bias of the sampling system, in the measurement of coal quality, can have significant commercial and environmental consequences.Bias as determined by these procedures need not be a constant or fixed value and can reflect the bias only under the conditions, which prevailed during the test period. Variables including, but not limited to, changes in the operation of the sampling system, the coal transfer operation, or the coal-sampling characteristics can cause changes in test results; therefore, if system bias is unacceptable, correct the cause rather than compensate for it.A single bias test may not provide a meaningful generalized expectation of past or future system performance but an ongoing testing program can. Such a program may be established by mutual agreement of the interested parties.Data used to draw conclusions regarding bias are subject to sources of error other than those attributable to the biases in the sampling system. Biases introduced by handling, preparation, and analysis of samples could also contribute to the appearance of a system bias. Therefore it is important to carefully follow ASTM standard methods for sampling, sample preparation, and testing, and to exercise careful quality control.In all cases, the test plan should approximate normal system operation and not be a source of bias itself. This is especially critical when the sampling system batch processes several consecutive increments at any stage. In this case, the system samples should consist of all the coal from an entire batch.Since this practice includes several different methods of sample collection and statistical procedures, the procedures used for both sample collection and statistical processing must be chosen before the test is conducted. This does not preclude subjecting historical test data to alternate statistical procedures for alternative purposes.1.1 This practice presents sample collection and statistical evaluation procedures for testing mechanical sampling systems, subsystems, and individual system components for bias. It is the responsibility of the user of this practice to select the appropriate procedure for a specific sampling situation.1.2 This practice does not purport to define an absolute bias. Bias defined by this practice is the difference between the population mean of the mechanical sampler test results and the accepted reference value.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.