Mean dead time

In the past, the acronym MTTR stood for "Mean Time To Repair." The term was changed in lEC 61508 because of confusion as to what was included. Some thought that Mean Time To Repair included only actual repair time. Others interpreted the term to include both time to detect a failure (diagnostic time) and actual repair time. The term "Mean Dead Time (MDT)" is commonly used in some parts of the world and means the same as Mean Time To Restore. 

Sample Transport Transport time, the time elapsed between sample withdrawal from the process and its introduction into the analyzer, shoiild be minimized, particiilarly if the analyzer is an automatic analyzer-controller. Any sample-transport time in the analyzer-controller loop must be treated as equivalent to process dead time in determining conventional feedback controller settings or in evaluating controller performance. Reduction in transport time usually means transporting the sample in the vapor state. 

Fractional dead time The mean fraction of time in which a component or system is unable to operate on demand. 

Dead time considerations in the alpha particle detection limit the count rate, and hence limit the neutron flux that can be used with this approach. This means that large scan times will probably be required with most implementations of this approach. 

Mean survival time of 1372 days 50% dead in 1457 days 50% dead in 1224 days 50% dead in 978 days anemia 50% dead in 653 days anemia 50% dead in 187 days anemia Leucocyte reduction in 6 days blood chemistry normal after 90 days Increased frequency of sister chromatid exchange at 0.005 Gy increased numbers of chromosomal aberrations at >0.02 Gy no significant increase in cell death Genes modifying cytoskeletal development adversely affected at all doses within 3 h by both high LET (neutrons) and low LET (gamma rays. X-rays) radiations... 

Beasley s derivation contains, however, as well as some probably trivial mathematical approximations, certain implicit assumptions that make this conclusion doubtful. He did not present a detailed kinetic scheme for the polymerization reaction, but it is implied by his Eq. (2) that the formation of branches is instantaneous after a new radical site has been produced on the dead polymer. That is, no account is taken of the fact that some growing radicals will be removed from the reactor before the growth of the new branch is completed. The mean time for growth of a branch is 1 /akp(M) and the ratio t of the mean residence time V/q to this time, Le. ... 

The mean residence time, 1, of a vessel is a key operating characteristic. If there is no dead space in the vessel,... 

The signal X can be introduced by means of an internal feedback loop within the controller (Fig. 7.60) which constitutes the dead time compensator GDTC(s) such that ... 

This means that the Smith compensator has moved the effect of the dead time outside the closed-loop as in the equivalent schematic representation in Fig. 7.61. 

Some disadvantages are associated with this system. A first disadvantage is the disappearance of the continuous character of the sensor since a certain period of time elapses between the measurement of electrical current at the sensor surface and the moment in time when the sample to be analysed leaves the process bath. Whereas the developed sensor is intrinsically a continuous working system, it is clear that a basically discontinuous system can be considered as virtually continuous when the duration of the measurement is situated below a specific critical threshold, the dead time for every considered application. One of the tasks of the research is to keep the dead time as short as possible, and if necessary take this into account when the global process is directed by means of the output signal of the sensor expanded with a FIA system. 

In a second series of experiments, the dead time is examined by means of the sensor signal at a liquid flow of 11/h. It is clear that when modifying, for example, the hydrogen peroxide concentration in the bath, this change will only be observed in the detection cell after a period of time. The length and the diameter of the tubes and the actual internal volume of the detection cell play an important part here. After changing the hydrogen... 

This means that one should bear in mind that the values of the process parameters detected at the sensor correspond to a situation which occurred in the bath of the process 30 s earlier. This is extremely important if one wishes to control the hydrogen peroxide concentration in the considered process. Though the dead time can be shortened by increasing the flow rate, the problem arises then that higher flow rates generate more waste-water and turbulent behaviour in the detection cell which affects the sensor signal. Similarly, the dead time of the same sensor expanded with the FIA system was verified with different flow rates (Fig.5.18). With a flow rate of, for example, 21/h, the dead time amounts to ca. 23 s. 

Dead time is the length of time, t, after a disturbance occurs before any change in the output is noticed and is illustrated for a first order process in Figure 4(c). It occurs particularly when material or energy is being transported some distance. Clearly it means that disturbance detection is slow and control actions are made on the basis of old measurements. Dead time is the most troublesome characteristic of a... 

The lipophilicity index q>0 was defined by Valko et al. (1993). cpo is the volume percent of organic modifier in the mobile phase by which the retention time is twice the dead time, which means the retention factor k is equal to 1. It was reported that using the cpo scale, the inter laboratory comparability was improved compared to using log kw. The correlation with traditionally determined log Pow values was shown to better (Valko 1993) using the cpo index. The analytical advantage of the cpo value is that it can be estimated from bracketing experimental results and not from extrapolation to 0 % organic modifier. 

If the mobile phase is compressible, the simple product of dead time and flow rate will be incorrect, and the dead volume must be taken as the product of the dead time and the mean flow rate. The dead volume has been shown to be given by [1]... 

Controversial opinions exist among scientists regarding the meaning of column dead time in LC [4]. In its broad sense, the term column dead time refers to the elution volume of an unretained and unexcluded... 

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