Drift Elimination Research Articles

96/02122 Methods of test for cooling tower drift eliminators

96/02122 Methods of test for cooling tower drift eliminators

Knowledge base for the systematic design of wet cooling towers. Part II: Fill and other design parameters

This paper describes the final part of the detailed methodology for the thermal design of wet, counterflow and crossflow types of mechanical and natural draught cooling towers. This part includes the following design steps: the fill or packing, total packed height and the number of decks, water and air loading, pressure drop across the packing, natural draught tower, fan design for a mechanical draught cooling tower, blowdown and make-up water rate, water distribution systems and drift eliminators. Different empirical relations and assumptions are used in this part of the design procedure.

5426969 Method for drift elimination in sensors : van Putten Mauritius H P M; van Putten Michel J A M; van Putten Antonius F P; van Putten Pascal F A M Santa Barbara, CA, 93106, United States

5426969 Method for drift elimination in sensors : van Putten Mauritius H P M; van Putten Michel J A M; van Putten Antonius F P; van Putten Pascal F A M Santa Barbara, CA, 93106, United States

Drift elimination in the calibration of scanning probe microscopes

Calibration of scanning probe microscopes (SPM) for atomic (molecular) resolution scans can be carried out on crystalline surfaces. However, SPM scans with atomic resolution are often affected by drift and hence would give false calibration factors. We propose a method which allows to calibrate the SPM instrument eliminating the effects of drift in a first-order approximation. Scans of the same surface are taken at different speeds and a linear regression is applied to the calibration factors calculated for each scan speed. Applying this method we succeeded in calibrating a commercial SPM system for atomic resolution scans with a precision of better than 2%.

Elimination of long-term calibration drift in molecular beam epitaxy by cooling the source flange

Drifts in the growth rate calibration with time constants of the order of hours are observed during molecular beam epitaxy growth, adversely influencing the calibration stability and reproducibility. The principal cause of these drifts was found to be high, time-dependent source flange temperatures (≳40 °C) at the thermocouple feedthroughs. The installation of water-cooled blocks on the furnace flanges eliminated this long-term drift and improved the calibration reproducibility by a factor of 3. In addition, these cooling blocks significantly reduced the ion-pump current in the growth chamber, presumably due to reduced outgassing of the source flange.

Full additive drift elimination in vector sensors using the alternating direction method (ADM)

A novel method of additive drift elimination in sensors, the alternating direction method (ADM), is presented. This paper will show that ADM can eliminate drift in vector sensors if these vector sensors have bidirectional (i.e., anisotropic) input characteristics for the physical entity S and have isotropic characteristics for any other possible physical input, where S is a vectorial quantity. The method is illustrated for air volume measurements using a bidirectional flow sensor, as previously described by one of the authors. The ADM volume signal is a signal that is free from drift, besides a small rest value, of which the absolute value is a priori bounded during the lifetime of the sensor. This ensures very reliable and accurate longterm air volume measurements, which is a powerful advantage of using ADM.

Calibration, drift elimination, and molecular structure analysis

A new automated technique for the estimation of the lateral calibration factors and for the drift in the fast scanning direction of SXM instruments is introduced. It is based on the detection of the reciprocal unit cell in Fourier space. The estimated calibration and drift factors are used for the restoration of distorted images containing self-assembled didodecylbenzene (DDB) molecules physisorbed on graphite. From the corrected images, the DDB unit cells are calculated in the Fourier domain. The long unit cell vector of the DDB molecules is calculated more accurately from images showing the graphite unit cells and the DDB lamellas simultaneously. By use of a correlation averaging technique, the structures of the DDB molecules within the unit cells are furthermore analyzed. The benzene ring and the C2H4 groups are thereby identified in the alkyl chains.

Scanning tunneling microscope calibration and reconstruction of real image: Drift and slope elimination

Drift, slope of sample, and indeterminate sensitivity of piezoceramics are considered as the origin of the linear scanning tunneling microscope (STM) image distortions. A special algorithm of STM scanning and reconstruction of image of unknown atomic structures is suggested and tested. This algorithm allows us to measure three components of the drift velocity and two angles, characterizing the average slope of scanning surface. On the one hand, using this algorithm, one can perform the STM calibration by a known surface structure (for example, the highly oriented pyrolytic graphite surface) even in the presence of a drift. This enables us to determine all the three piezoceramics constants of STM piezoscanner and the deviation of the real scanner axes X and Y from orthogonality. On the other hand, using such a calibrated STM and the described algorithm, it is possible to obtain the real STM image and make measurements for unknown surfaces with atomic resolution without the distortions mentioned above. As it has been proved, the error of interatomic distance measurements does not exceed 5% (∼0.1 Å) for any direction along the surface, even in the presence of a drift up to 0.4 Å/s and the sample slope angle up to 10°.

Elimination of frequency drift from Fourier transform ion cyclotron resonance mass spectra by digital quadrature heterodyning: ultrahigh mass resolving power for laser-desorbed molecules

At sufficiently low pressure, FT-ICR mass resolving power is no longer pressure-limited. Rather, the observed spectral peaks are broadened by ion cyclotron frequency drift during the detection period, due to change in shape of the coherently orbiting ion packet during detection. The frequency drift may be quantitated by Fourier transformation of each of a series of consecutive segments of the time-domain ICR signal, followed by fitting the frequency vs time behavior to a polynomial in time. Correction for that frequency drift is then achieved by a digital quadrature procedure, followed by multiplication by a weight factor which removes the frequency drift. We demonstrate a 750-fold reduction in FT-ICR mass spectral peak width for pseudomolecular (M+K)+ ions of laser-desorbed leucine enkephalin (m/delta m = 1,300,000)! Moreover, correction based on the frequency drift of ions of a given m/z also corrects for frequency drift of ions of other m/z values, as demonstrated for isotopic peaks from (M+K)+ from gramicidin S (m/z 1179). Narrowing of the FT-ICR mass spectral peaks results in a corresponding increase in peak height-to-noise ratio as well. In addition, we propose a theoretical model for frequency drift during detection of the ion cyclotron resonance signal. Simultaneous relaxation of coherent cyclotron motion and compression of the axial distribution of an initially radially coherent ion packet account for ion cyclotron frequency drift during detection. The potential energy generated by mutual ion-ion Coulomb repulsions varies with ion cyclotron orbital radius as ions undergo collisional damping.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Drift Eliminator Design on Cooling Tower Performance

In the use of wet cooling towers, drift refers to small droplets of circulating water that are carried out of the cooling tower by the saturated exhaust air. Inertial impaction separators, known as drift eliminators, are used to strip the water droplets from the exhaust air. To achieve peak cooling tower operating efficiency, it is desirable that losses in fan system performance due to the drift eliminators be minimized. Therefore, an experimental program was developed and executed to evaluate the effect of drift eliminator design on cooling tower fan system performance. Flow visualization studies were used to gain insight into the flow patterns within the cooling tower plenum as influenced by drift eliminator design. A fully instrumented fan test cell was used to investigate the effects upon fan system performance resulting from two different styles of drift eliminators. The effect of drift eliminator discharge angle upon fan system total efficiency was investigated and the optimal discharge angle determined.

Suppression Method of Disturbance Torque Due to System Drift via an Observer in the Robot Control System

The degradation of performances in the robot manipulator control system results from disturbance torques due to the system drift, frictions in the gears, Coriolis, gravity loading, and centrifugal effects of the link. The torque due to the system drift is closely related to the difference between ground levels and the variation of characteristics of the control system, while the others depend on the manipulator's physical parameters, instantaneous joint configuration, joint velocity and acceleration, and the load it is carrying. In this paper, an estimation algorithm of the system drift in the robot manipulator control system is proposed, which is based on the gradient search method. This algorithm is executed in the steady state for the elimination of the system drift because the variation of the characteristic of the control system due to the change in temperature, supply voltage, and etc. are slow compared with the motion of the robot manipulator. The proposed algorithm is implemented on the control system for a robot manipulator with six degrees of freedom, which has an 80386/80387 as a main processor and a TMS 320C30 as a processor for motion control. Experimental results show that the proposed suppression method of the system drift via an observer can be effectively used in controlling robot manipulators with high dynamic performance at both the transient and steady states.

Temperature‐dependent spot positional variability in two‐dimensional polypeptide patterns

The effect of temperature, at which isoelectric focusing with immobilized pH gradients is performed, on spot positions and pattern quality in two-dimensional (2-D) electrophoresis was examined. Increased temperatures revealed improved 2-D patterns with respect to sample entry, resolution, and background staining. Focusing at 20 degrees C was superior to focusing at 10 and 15 degrees C. Even at 30 degrees C, a pattern of well-resolved polypeptide spots with a minimum amount of horizontal streaking at the basic end was observed. A computer-based analysis showed that a substantial proportion of polypeptides assumed altered positions in the 2-D pattern in relation to temperature. Mobility shifts of polypeptides were more variable on the neutral part than on the acidic or basic end. The mobility shifts were not restricted to one direction for all the spots whose migration was altered. However, for any given spot, the direction was the same with subsequent increments of temperature. The results clearly demonstrate that a defined temperature for first-dimensional isoelectric focusing is a requirement for the reproducibility of 2-D electrophoresis. After elimination of the cathodic drift, a major source of variability in 2-D patterns, associated with carrier ampholytes, temperature control becomes a critical parameter.

A dual six-port automatic network analyzer incorporating a biphase-bimodulation element

Current state-of-the-art dual six-port automatic network analyzers (ANAs) are dependent upon mechanical phase shifters and attenuators. Slow measurement and calibration are among the factors that have prevented six-port ANAs from more general use outside standards and research laboratories. Biphase bimodulation, a technique which removes the requirements for mechanical phase shifters or attenuators, is introduced. The technique provides improved sensitivity and elimination of drift as a consequence of AC modulation. A significant increase in measurement speed is achieved, allowing quasi-real-time evaluation of scattering parameters. An experimental prototype dual six-port ANA is described, and results obtained using the technique are given. >

Pulsed coulometric detection with automatic rejection of background signal in surface-oxide-catalyzed anodic detections at gold electrodes in flow-through cells

A variation of Pulsed Coulometric Detection (PCD) is described in which the detection potential is scanned in a cyclic fashion during current integration to achieve automatic and virtual elimination of baseline drift caused by surface roughening and changes in pH. The technique is examined at a Au electrode for flow-injection determination if thiourea which is typical of numerous sulfur compounds whose anodic reactions are catalyzed by formation of surface oxide. The baseline decays quickly to a near-zero equilibrium value following start-up and is unchanged for a pH step of ca. 2 units. The technique is concluded to be compatible with pH-gradient chromatography.

Measurement of plasma phenytoin by EMIT in the Monarch centrifugal analyzer: studies on the elimination of within-rotor drift.

We investigated the measurement of phenytoin in plasma by the EMIT method, in the Monarch centrifugal analyzer. When we used the standard protocol supplied by Instrumentation Laboratory, significant drift was observed across a full rotor loaded with 31 replicates of a single specimen. Although the cause remains obscure, the drift was eliminated by using a load-spin-reload-spin procedure. This makes it possible to analyze large batches of samples without excessive use of standards and reagents.

Method for an automatic analysis of the ECG

A method is presented for an analysis of the ECG. Using cubic spline techniques we proceed first to a smoothing of the signal and then to the elimination of baseline drift. The properties of the calculated derivatives are used to establish criteria for the identification of the ECG waves and the measurement of their essential parameters. The complete procedure can be carried out by a computer, without human intervention. The results of this fully automatic procedure can be used directly as a means of classifying the ECG.

Spatial Structure in Drosophila buzzatii Populations: Simple and Directional Spatial Autocorrelation

The spatial structure of 12 allele frequencies was examined for 57 populations of the cactophilic fly Drosophila buzzatii from eastern Australia. Techniques include spatial-autocorrelation analysis and the newly developed directional spatial autocorrelation. Although 11 allele frequencies differ among localities, only 6 show spatial structure along one dimension. Directional correlograms support clines or major geographic trends in different directions for 5 allele frequencies. Spatial correlograms were also computed for genetic distances. The overall results-genetic heterogeneity among localities, weak correlation between allele-frequency surfaces, moderate spatial structure, and moderate parallelism of correlograms-permit elimination of genetic drift, selection against a single environmental gradient, or the effects of a single migrational event, and they suggest that selection operates on different spatial scales ranging from a continental one to a strictly local one. These results are interpreted in terms of the known history and biology of these organisms in Australia and are compared with spatial analyses of allele frequencies in other organisms.

Kerr effect in an optical passive ring-resonator gyro

The Kerr effect in an optical passive ring-resonator gyro (OPRG) is analyzed considering the optical source coherence. This effect causes the drift to be much greater than the theoretical limit of rotation sensing given by the detector shot noise for an OPRG with high sensitivity. The drift depends not only on the fluctuation of the power splitting ratio between two counter-propagating beams in the resonator, but also on the frequency modulation indices used to set the operating point. Square-wave intensity modulation of the incident beam is also discussed as a way to eliminate the drift. It is found that the ratio of the signal-beam round-trip time in the resonator to the modulation period must be an integer to optimize the drift elimination. From the practical viewpoint, the requirement for the modulation parameters is analyzed numerically.

Elimination of Drift and Asymmetry Effects in Fluidic Sensors by Feedback

This paper presents a feedback approach to the design of fluidic sensor circuits that will minimize drift and other unwanted offset effects, that are due to component asymmetries, and at the same time will improve the overall sensor frequency response. In this approach sensor supply pressure is generated by one output of a high gain differential regulator amplifier rather than by the raw system supply pressure. As a result, variations in system pressure, that normally would appear as sensor output drift (time varying null offset), are decoupled from the sensor. The amount of effort required to keep the sensor nulled becomes the sensor system output. When this feedback is implemented the overall dynamic response can be improved by a reduction in the fundamental circuit time constant, that is governed by the sensor dynamics, by introducing phase lead and so reducing the low frequency phase shift. Since the error signal driving the high gain regulator is proportional to the degree of sensor asymmetry, output performance of the feedback system is actually enhanced by having significant null offset characteristics. The offsets generally found in photochemically etched amplifiers and laminar jet angular rate sensors are shown to be reduced by two orders of magnitude and frequency response improved by as much as a factor of five. This technique has been applied to rate sensors, resistance bridges, pressure regulators, and airspeed sensors.

Roller-Wiper Herbicide Applicator: Control of Right-Of-Way Hardwood Brush

The application of herbicides to target plants by using contact method such as wicks or absorbent wipers has several advantages over spraying in many circumstances. Elimination of herbicide drift, conservation of herbicide material, and plant height selectivity are characteristic of most contact application methods. An analysis of the most suitable method of applying translocatable herbicides to woody brush was carried out in field and laboratory tests. A horizontal, rotating, carpet-covered roller was used in test plots and on utility rights-of-way to treat a wide variety of woody brush using seven translocatable herbicides. An average of over 90% brush control was achieved in these tests. Laboratory testing studied variations in the roller speed, roller diameter, carpet covering, wiper flap pressure, liquid surface tension and liquid viscosity in order to determine optimal levels for these application parameters. Mathematical models are developed for predicting the behavior of liquid added to the top of the rotating cylinder. More than 86% of the variation in the amount of liquid held on the roller could be attributed to the variables studied. Field studies indicated that the roller-wiper concept of herbicide application is very effective in controlling unwanted woody brush. It was determined that by controlling the proper parameters, an efficient, reliable, safe herbicide applicator could be built using the carpet roller principle.