Dead-time Value Research Articles

Maximum Efficiency Point Tracking (MEPT) Method and Digital Dead Time Control Implementation

An adaptive control method, to be called maximum efficiency point tracking (MEPT), is presented in this paper. This method tracks system efficiency, which is dc-dc converter efficiency in this paper, and adaptively optimizes system parameters to maximize efficiency. The MEPT method is used in this paper to optimize the primary-to-secondary switches' dead-time parameter in an isolated topology to reduce the switches' body diodes conduction during commutation periods and to reduce body diodes conduction and reverse-recovery related losses in order to improve efficiency. MEPT tracks converter efficiency while changing the dead-time and detects the optimized dead-time value at the maximum efficiency point at different load and line conditions. In this paper, the MEPT method is discussed and analyzed, and its digital control algorithm and experimental implementation are presented

Application of the maximum bubble pressure technique for dynamic surface tension studies of surfactant solutions using the Sugden two-capillary method

Exact knowledge of the dead time as part of the bubble lifetime in the maximum bubble pressure method is an important prerequisite for accurate dynamic surface tension measurements. The duration of the dead time depends essentially on the capillary geometry and affects significantly the measured surface tensions of concentrated surfactant solutions. Increase of the dead time leads to a significant surface tension decrease of a freshly formed bubble surface due to the significantly higher residual adsorption of the surfactant molecules. It is shown that correct dynamic surface tensions are obtained with the experimental procedure of Sugden's method only when in addition to the fixed frequency of bubble formation, also the dead time values for the two capillaries are kept constant.

Standardization of 222Rn by LSC and comparison with [formula omitted]- and [formula omitted]-spectrometry

Liquid scintillation counting (LSC) was used for the measurement of 222Rn in equilibrium with its daughters, with detection efficiency close to 5. The appropriate corrections were considered, including one related to the probability that the 165-μs half-life 214Po decays during the dead time of the counter initiated by the disintegration of his parent nuclide, 214Bi. The dead-time determination of a commercial LS counter is also presented using a 222Rn standard source. The LSC 222Rn sources were prepared by transfer of 222Rn produced by a solid 226Ra source into LSC cocktail frozen at 77 K, flame-sealed afterwards. They were measured using the LNHB triple coincidence counter with adjustable extending-type dead-time unit, between 8 and 100 μs; two different procedures were used to calculate an effective dead time and then to deduce the counting rate extrapolated to zero dead-time value. The LSC results were compared with those obtained by cryogenic α -particle spectrometry (LNHB system) and by γ -ray spectrometry for the same radon source in the LSC vial; the geometry transfer coefficient was calculated using the ETNA software. Measurement results and uncertainties are discussed.

Validation of GATE Monte Carlo simulations of the GE Advance/Discovery LS PET scanners

The recently developed GATE (GEANT4 application for tomographic emission) Monte Carlo package, designed to simulate positron emission tomography (PET) and single photon emission computed tomography (SPECT) scanners, provides the ability to model and account for the effects of photon noncollinearity, off-axis detector penetration, detector size and response, positron range, photon scatter, and patient motion on the resolution and quality of PET images. The objective of this study is to validate a model within GATE of the General Electric (GE) Advance/Discovery Light Speed (LS) PET scanner. Our three-dimensional PET simulation model of the scanner consists of 12 096 detectors grouped into blocks, which are grouped into modules as per the vendor's specifications. The GATE results are compared to experimental data obtained in accordance with the National Electrical Manufactures Association/Society of Nuclear Medicine (NEMA/SNM), NEMA NU 2-1994, and NEMA NU 2-2001 protocols. The respective phantoms are also accurately modeled thus allowing us to simulate the sensitivity, scatter fraction, count rate performance, and spatial resolution. In-house software was developed to produce and analyze sinograms from the simulated data. With our model of the GE Advance/Discovery LS PET scanner, the ratio of the sensitivities with sources radially offset 0 and 10 cm from the scanner's main axis are reproduced to within 1% of measurements. Similarly, the simulated scatter fraction for the NEMA NU 2-2001 phantom agrees to within less than 3% of measured values (the measured scatter fractions are 44.8% and 40.9 +/- 1.4% and the simulated scatter fraction is 43.5 +/- 0.3%). The simulated count rate curves were made to match the experimental curves by using deadtimes as fit parameters. This resulted in deadtime values of 625 and 332 ns at the Block and Coincidence levels, respectively. The experimental peak true count rate of 139.0 kcps and the peak activity concentration of 21.5 kBq/cc were matched by the simulated results to within 0.5% and 0.1% respectively. The simulated count rate curves also resulted in a peak NECR of 35.2 kcps at 10.8 kBq/cc compared to 37.6 kcps at 10.0 kBq/cc from averaged experimental values. The spatial resolution of the simulated scanner matched the experimental results to within 0.2 mm.

Determination of total lead and lead isotope ratios in natural waters by inductively coupled plasma time-of-flight mass spectrometry after flow injection on-line preconcentration

An on-line flow injection (FI) preconcentration method is developed for the determination of total lead and lead isotope ratios in natural waters by inductively coupled plasma time-of-flight mass spectrometry (ICP-TOFMS). This method yields a 20-fold enrichment compared to the direct FI determination and provides improved isotope ratio precision. Besides, the high selectivity achieved, particularly towards Hg, allows the accurate determination of 204 Pb -based isotope ratios at ng l −1 Pb levels with a good precision. Precise transient Pb isotope ratios in ion counting are affected by detector dead time; a dead time value of 20 ns was used for correction for Pb concentrations in excess of 0.4 μg l −1, and a 100 μl eluent loop. Mass discrimination (MD) was evaluated for pairs of isotopes using an isotopic standard reference material (NIST 981). The precision obtained for 204 Pb/ 206 Pb , 207 Pb/ 206 Pb , and 208 Pb/ 206 Pb ratios at a Pb concentration of 1 μg l −1 was 1.87, 0.7, and 0.28% relative standard deviation (R.S.D.) respectively, using ion counting mode, 1.0 s integration time and calculations performed using full peak integration. Lead concentrations in the water samples were between 210 and 462 ng l −1. Precisions (for n=5) were found in the ranges 1.5–4.25% and 0.1–0.8% for 204 Pb/ 206 Pb and for 207 Pb/ 206 Pb , 208 Pb/ 206 Pb ratios.

A self-tuning fuzzy PI controller

A robust self-tuning PI-type fuzzy logic controller (FLC) is presented. Depending on the process trend, the output scaling factor (SF) of the controller is modified on-line by an updating factor ( α). The value of α is determined from a rule-base defined on error ( e) and change of error ( Δe) of the controlled variable. The proposed self-tuning controller is designed using a very simple control rule-base and the most natural and unbiased membership functions (MFs) (symmetric triangles with equal base and 50% overlap with neighboring MFs). The proposed scheme is tested for a wide variety of processes including a marginally stable system with different values of dead time. Performance comparison between the conventional PI-type and proposed self-tuning FLCs is made in terms of several performance criteria such as peak overshoot, settling time, rise time, integral absolute error and integral-of-time-multiplied absolute error, in addition to the responses due to step input and load disturbance. Results for various processes show that the proposed FLC outperforms its conventional counterpart in each case.

Tuning Proportional−Integral Controllers for Processes with Both Inverse Response and Deadtime

Many tuning methods have been proposed over the last half-century. Most apply to deadtime/lag processes, but several have studied either integrating processes or inverse response processes. Very few have explored processes in which both deadtime and inverse responses occur. This type of response is observed in adiabatic tubular reactors when reactor outlet temperature Tout is the controlled variable and reactor inlet temperature Tin is the manipulated variable. Typically the control structure uses a cascade arrangement in which the secondary loop uses furnace heat input or heat-exchanger bypassing to control Tin. This paper addresses the problem of controlling processes that exhibit both inverse response and deadtime. The Ziegler−Nichols tuning method recommended in the literature is shown to give poor performance at both small and large values of deadtime and positive-zero time constant. A new tuning method is proposed in which the PI tuning constants are presented as functions of the positive zero τz and the deadtime D. Results are given in the form of easy-to-use tuning charts.

A calculation method based on isotope ratios for the determination of dead time and its uncertainty in ICP-MS and application of the method to investigating some features of a continuous dynode multiplier

A method for the determination of dead time (and its uncertainty) of the ion-counting detection system of ICP-MS instruments is presented. It is based on isotope ratio measurements, which are more precise than ion current measurements and will result in values for the dead time with a measurable uncertainty. The suggested method allows us to estimate the uncertainty associated with the dead time. Typical relative uncertainties of the dead time values were found to be in the range of 10-20%.

A Self-Tuning Fuzzy PD Controller

In this article we present a self-tuning PD-type fuzzy logic controller (FLC). The output scaling factor (SF) of the proposed controller is modified on-line by an updating factor (α) according to the process trend. The value of a is determined from a rule-base defined on error (e) and change of error (Δe) of the controlled variable. The proposed self-tuning FLC is designed using a very simple control rule-base and the most natural and unbiased membership functions (MFs) (symmetric triangles with equal base and 50% overlap with neighbouring MFs). The effectiveness of the scheme is established through simulation experiments on various types of second order processes such as (i) marginally stable, (ii) non-linear and (iii) non-minimum phase-pole (unstable) systems with different values of dead time. Performance of the proposed self-tuning FLC is compared with that of its conventional counterpart with respect to both step set-point change and load disturbance using several performance indices. In each case the proposed controller shows remarkably improved performance over the conventional one.

Measurement and prediction of dead times and column diameter in capillary gas chromatography by using air, methane and some solvents

The experimental determination of the hold-up time of capillary columns when using flame ionisation detection is generally made by measuring the retention time of methane. In high-temperature analysis or when using specific detectors the front of the solvent peak is often taken empirically as the dead time marker. An evaluation of the accuracy of these procedures was carried out by taking into account the errors due to the selection of the peak front or apex. The behaviour of these values as a function of temperature was studied by using capillary columns coated with liquid phases of different polarity (polydimethylsiloxane and polyethylenglycol). The dead time values measured by injecting small amounts of inorganic gases, methane, methanol, dichloromethane and hexane, were compared with those calculated with Poiseuille's law using the column length and diameter and the carrier gas viscosity. The accuracy and precision of the dead time values differ when the retention times of various compounds and of the apex or front of their peaks is used. The effect of the uncertainty of the diameter of the column given by the manufacturer on the dead time calculation was investigated and a method for the determination of the diameter by using experimental measurement of retention times is suggested.

On the Measurement of Dead Time in Micellar Liquid Chromatography

Abstract Modelling of the retention of solutes in micellar liquid chromatography allows the optimization of the resolution of a mixture of solutes and the determination of physico-chemical retention parameters. Both tasks imply the calculation of capacity factors, which are severely affected by the value of dead time. However, the determination of the dead time is not easy when a micellar mobile phase is used owing to the wide and variable perturbations that appear at the heads of the chromatograms. Four different criteria of determination of a reference time in the chromatograms are proposed and compared. The criteria are applied to mobile phases containing a varying concentration of surfactant and modifier, in order to observe the dependence of the reference time with the mobile phase composition. The study of the influence of the errors in the dead time on the modelling of the retention indicated that an accurate dead time is necessary to calculate retention parameters, but an excellent prediction of r...

A note on the statistical characteristics of a two-unit system

Expressions for the Laplace transforms of reliability and availability functions are obtained for a two-unit system, with different repair times for the units which have failed from online and standby states, and a dead time value for the repair facility by the use of regeneration point technique. The system consists of two-units with one repair facility. The repair facility is not available for a random time immediately after each repair completion. From the Laplace transforms of reliability and availability functions the steady state availability, reliability and mean time to system failure can be obtained.

Precise measurement of dead time

Four methods are discussed by which dead times of the non-extending type can be determined experimentally. Two methods using statistical pulses were improved by eliminating uncertainties due to counting statistics. However, it was concluded from a comparison of the four methods that those using periodical pulses are not only less time-consuming but are preferable if high-precision values are aimed at. A dead-time unit with quartz oscillator-based dead times of the non-extending type was tested using all of the four methods. Measurements within a period of three years indicated that the unit investigated here has subnanosecond stability for each of the adjusted dead-time values.

Deadtime measurement and associated statistical uncertainty by means of a two-detector paired-source method

A brief description of the two-detector paired-source method for determining the deadtime of a counting system is given. A very simple formula for accurately estimating the statistical uncertainty of the deadtime value is derived. The error formula has been carefully checked against experimental measurements.

A simple procedure for determination of the dead time of a stopped-flow instrument.

The reducing reaction of 2,6-dichlorophenolindophenol by L-ascorbic acid was used to determine the dead time of a stopped-flow instrument. Because this reaction is irreversible, the dead time could be determined by a simple graphical analysis. The dead time values determined by the present method were comparable to those by other methods previously reported.

CAMAC/MBD interface for the VAX data acquisition facility at the KFUPM Energy Research Laboratory

The authors describe the CAMAC/MBD (microprogrammable branch driver) data acquisition interface used with the VAX 11/785 computer system at the Energy Research Laboratory (ERL) of King Fahd University of Petroleum and Minerals, Dhahran, Saudia Arabia. An ERL-developed automatic LAM (look-at-me) multiplexer module is described. Details of a simple and efficient scheme for the acquisition of multiparameter data are highlighted, and performance results are given. The hardware uses fast CAMAC analog-to-digital converter modules with constant conversion time. This has considerably simplified the interface hardware and allowed higher data rates to be acquired at lower values of deadtime in comparison with similar installations. >

Estimating the robust dead time for closed-loop stability

A method based on the small-gain theorem is provided for estimating the robust dead time for closed-loop stability. The method lends itself to generalization for multivariable systems and also to graphical implementation. Some examples are provided to demonstrate the use of the method, and the results are compared to the exact critical values of dead time.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurement of column dead time in capillary gas chromatography

Two simple methods are given for calculation of accurate values of column dead time (tM) from the unadjusted retention times of liquid n-alkanes. Both are iterative methods that are based on the linearity of a plot of log k' against the carbon number of the alkanes. One can be done on an ordinary programmable calculator; the other uses a simple matrix-manipulation com- puter program. These methods also provide a simple way to measure Kovits indices.

Instrumental dead-time and its relationship with matrix corrections in x-ray fluorescence analysis

The relationship between instrumental dead-time and the self-absorption coefficients, α ii, in x.r.f. matrix correction by means of influence coefficients, is not generally recognized but has important analytical consequences- Systematic errors of the order of 1% (relative) for any analyte result from experimental uncertainties in instrumental dead-time. Such errors are applied unevenly across a given range of concentration because the error depends on the calibration standards and on the instrumental conditions used. Refinement of the instrumental dead-time value and other calibration parameters to conform with influence coefficients determined elsewhere assumes exact knowledge of dead-time of the instrument used originally, and quite similar excitation conditions and spectrometer geometry for the two instruments. Though these qualifications may not be met, adjustment of any of the parameters (dead-time, reference concentration, background concentration, self-absorption and other influence coefficients) can be easily achieved.