Repeatability volume measurement

Anyone making a measurement has a responsibility to indicate the uncertainty associated with it. Such information is vital to someone who wants to repeat the experiment or judge its precision. The three volume measurements referred to earlier could be reported as... 

Systematic errors usually arise from specific shortcomings in the measuring instrument, the observer, or the way in which the measurement is taken. Sources of systematic error include a badly calibrated measuring device, a faulty instrument movement, an incorrect action by the experimenter (e.g., misreading a volume measurement), or the parallax effect when incorrectly viewing a scale. Repeating the measurement does not necessarily help, because the error may be repeated, and the analyst may... 

Previously, we discussed the need to know when a weight measurement does and does not need to be precise so that the appropriate balance is chosen for the measurement. We now repeat many of our previous comments, but for volume measurements rather than weight. 

It is worthwhile to discuss the components of the standard uncertainty of a volume measurement here. The repeatability may be independently assessed by a series of fill-and-weigh experiments with water at a controlled temperature (and therefore density) using a balance so that the uncertainty of weighing is small compared with the variation in volume. Although this may be instructive, if the whole analysis is repeated, say, ten times, then the repeatability of the use of the pipette, or any other volume measurement is part of the repeatability of the overall measurement. This shows the benefit, in terms of reaching the final estimate of measurement uncertainty more quickly, of lumping together uncertainty components. 

Using your metric ruler, determine the dimensions of the block (length, width, height) and record the values to the nearest 0.01 cm (1). Calculate the volume of the block (2). Repeat the measurements for a second trial. 

The (J-Repeat. and the corresponding degrees of freedom, Repeat., are also extracted directly from the repeatability tests. Such tests consist of successive weighings of water volumes measured by the instrument. The observed standard deviation is a function of the analyst s expertise. 

It is useful to note that statistical handling for a relatively small number of systematically planned measurements may yield more information than a large number of repeated identical measurements. Consider triplicate analysis of the same sample using different weights or volumes. This may reveal errors that would not be detected if repeated similar sample sizes were taken. A report entitled Principles of Environmental Analysis [2] which can be applied to all types of analyses, states ... 

The repeated angular measurements on crystals of various forms had filled volumes. However, contrary to the views of Haiy concerning a close correspondence between crystalline form and chemical composition, these measurements brought no useful contribution to systematic mineralogy except for the possibility of verifying the existence of polymorphs and the presence of isomorphic series. 

PVT measurements The PVT apparatus from Gnomix Research was described in detail elsewhere. The sample cell was filled with approximately 1 g polymer and mercury. The cell was closed on one end by a flexible bellows and the expansion was measured with changing temperature in order to determine the volume. In the isothermal mode volume measurements were carried out at fixed pressure intervals (10 MPa) in the range from 0 to 200 MPa. The process was repeated for temperature intervals of approximately 10 C. In order to obtain the characteristic or hard core parameteis P, Vj and T, the experimental data were fitted to Flory s equation-of-state (EOS) by using a nonlinear least squares fit... 

Earlier, Helm [126] allowed the beer to flow through a special pourer from a bottle mounted a fixed height above a cylindrical separating funnel. After two minutes the beer which had separated was drawn off (volume a) and after a further eight minutes this process was repeated (volume b). The residual foam was then collapsed with ethanol (3 ml) and the volume measured (c) after allowing for the ethanol. From these results are calculated ... 

When you begin the actual experiment, keep your notebook nearby so you will be able to record those operations you perform. When you are working in the laboratory, the notebook serves as a place in which to record a rough transcript of your experimental method. Data from actual weighings, volume measurements, and determinations of physical consfants are also noted. This section of your notebook should not be prepared in advance. The purpose is not to write a recipe but rather to record what you did and what you observed. These observations will help you write reports without resorting to memory. They will also help you or other workers repeat the experiment in as nearly as possible the same way. The sample notebook pages found in Figures 2.2 and 2.3 illustrate the type of data and observations that should be written in your notebook. 

Almgren et aL (1982) have reported a precision of 0.2 % for this method, but differences as high as 1 % between repeat determinations. As with the potentimnetric titration methods, accuracy will depend to a large degree on the accurate of the volume measurements and of the hydrochloric acid concentration. 

Measurement 25 cm TISAB 11 and 25 cm sample are mixed in a measurement cell. With the electrodes dipped into the solution and stirring continuously the cell potential is measured (Ei). Then small volume (Va) of standard solution of known concentration (Cs) is added and the electrode potential is again measured (E2). The difference AE = IE2 Ei must be in the range of 8-30 mV. The measurement is repeated with smaller volume or more diluted standard when AE > 30 mV, while at AE < 8 mV sample dilution must be done before repeating the measurement. Multistandard addition resulting in AEi, AE2, and AE3 values can be performed for increasing the accuracy therefore the slope value should be checked. It is a good idea to keep AE3 value smaller than 30 mV. 

Bakker J, Olree M, Kaatee R, de Lange EE, Moons KG, Beutler JJ et al (1999) Renal volume measurements accuracy and repeatability of US compared with that of MR imaging. Radiology 211 623-628... 

Prepare a solution of hydrogen peroxide by diluting 25.0 cm (100 volume) (measured by a burette) to 250 cm Use a burette to deliver 50.0 cm of the freshly diluted solution to a conical flask, acidify and titrate against standardised 0.02 M permanganate to the first permanent pink. Repeat and calculate, from the average titre, the concentration of hydrogen peroxide in mol dm . ... 

A repeatable volume of the specimen to be analyzed is precisely injected into a gas chromatograph equipped with a flame ionization detector (FID). The peak area of each impurity is measured. Concentration of each impurity is determined from the linear calibration curve of peak area versus concentration. Purity by gas chromatography (GC) is calculated by subtracting Ae sum of the impurities found from 100.00. Results are reported in weight percent... 

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