105,828 research outputs found
On a Relation between the Flicker value and the Working Condition
No full textThe appropriate disposition of the worker improves the ability of the worker and the efficiency of the labor and further decreases the rate of inferior goods and the rate of accidents. In previous paper, the variation of the flicker value, the trend of the miss frequency and the relation between them under the condition which has one surveillance point and one back-ground condition are analyzed. In this paper, the surveillance point is increased to two points and the back ground condition also two in order to examine which condition influences strongly to the flicker value in the working time. It was found that the variation of the flicker value is strongly connected with the qualification, the number of the surveillance and its miss-frequency
Flicker Observer Effect: Guiding Attention Through High Frequency Flicker in Images
No full textDrawing the user's gaze to an important item in an image or a graphical user interface is a common challenge. Usually, some form of highlighting is used, such as a clearly distinct color or a border around the item. Flicker can also be very salient, but is often perceived as annoying. In this paper, we explore high frequency flicker (60 to 72 Hz) to guide the user's attention in an image. At such high frequencies, the critical flicker frequency (CFF) threshold is reached, which makes the flicker appear to fuse into a stable signal. However, the CFF is not uniform across the visual field, but is higher in the peripheral vision at normal lighting conditions. Through experiments, we show that high frequency flicker can be easily detected by observers in the peripheral vision, but the signal is hardly visible in the foveal vision when users directly look at the flickering patch. We demonstrate that this property can be used to draw the user's attention to important image regions using a standard high refresh-rate computer monitor with minimal visible modifications to the image. In an uncalibrated visual search task, users could in a crowded image easily spot the specified search targets flickering with very high frequency. They also reported that high frequency flicker was distracting when they had to attend to another region, while it was hardly noticeable when looking at the flickering region itself.Computer Graphics ForumFocus and Virtual Environments36
Flicker mitigation in industrial systems
No full textThesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006.This thesis investigates the compensation of voltage flicker in an industrial environment. Industrial
loads draw progressively less sinusoidal currents. These currents cause non-sinusoidal voltage
drop over the line impedance, causing a distorted line voltage. The light output of incandescent
electric lighting systems is quadratically proportional to the line voltage, and thus variations in the
line voltage cause irritating variations in the output of such systems.
Two tools to analyse flicker problems are developed: A USB data logger is built to log measured
waveforms to computer hard disk. These data are analysed using a MATLAB implementation of the
IEC-specified flicker meter.
A converter-based flicker compensator is found to be the only compensator capable of
compensating general flicker loads. Such a compensator is developed using the synchronous
reference frame filtering technique. Several aspects of the compensator are dealt with in detail
including selection of a current control strategy, calculation and implementation of the converter
duty cycles and compensation of the various non-idealities in such a controller.
Full compensation is contrasted to reactive compensation – the second option being less
expensive but also less effective in the compensation of certain loads. The effectiveness of reactive
compensation is found to be dependent not only on the type of load, but also on the type of line
feeding the flicker load.
Three industrial flicker loads are measured and analysed: a three-phase welder, a sawmill and a
rock crusher. These loads are simulated, and the compensation proposed confirmed via these
simulations. The compensation of the three-phase welder is tested using a hardware scale model.
This verified the operation of the proposed flicker compensator in practice
Flicker Photometer
No full textA flicker photometer was used in the early 20th century for the measurement of luminous flux and other properties related to photometry. This example is a Koenig-Martens flicker photometer for an early spectral transmissometer, later to be called a spectrophotometer. The latter name arose because it was the result of combining a spectrometer with the visual flicker photometer. The sphere source served only as an intensity reference and the monochromatic beam from the spectrometer was introduced into the photometer and displayed in series with the reference light. The optical path between the sphere and the beam switcher contains a pair of polarizing prisms which are used to extinguish some or all of the reference light down to the luminance of the spectral beam. Later, this method was used by Arthur Hardy at MIT to produce a photoelectric spectrophotometer, replacing the eye with a phototube and a servo motor to rotate the analyzer prism to obtain a minimally flickering signal out of the phototube.32 x 40 x 34 c
A Time Domain Behavioral Model for Oscillators Considering Flicker Noise
No full textThe phase noise behavior due to flicker noise of an oscillator has not been modeled accurately by a time domain behavioral model. In this paper, the mathematical foundation to model the up-converted flicker noise region of the phase noise is discussed and derived in detail. Based on the foundation, we present a time domain behavioral model of the oscillator and implement it in Simulink. Comparisons show that the model is as precise as the direct transistor-level circuit simulation, whether in the up-converted thermal or flicker noise region.NSFC [61471011]; R&D projects of Shenzhen city [JCYJ20150331102721193, JCYJ20160229094148396]CPCI-S(ISTP)469-47
New trends in active filters for improving power quality
No full textSince their basic compensation principles were proposed around 1970, active filters have been studied by many researchers and engineers aiming to put them into practical applications. Shunt active filters for harmonic compensation with or without reactive power compensation, flicker compensation or voltage regulation have been put on a commercial base in Japan, and their rating or capacity has ranged from 50 kVA to 60 MVA at present. In near future, the term of active filters will cover a much wider sense than that of active filters in the 1970s did. The function of active filters will be expanded from voltage flicker compensation or voltage regulation into power quality improvement for power distribution systems as the capacity of active filters becomes larger. This paper describes present states of the active filters based on state-of-the-art power electronics technology, and their future prospects toward the 21st century, including the personal view and expectation of the author</p
Empirical model of flicker in silicon light valves
No full textWe have performed systematic characterizations of flicker in silicon light valves. It was found that temperature was the most important factor associated with flicker. Temperature could assist conduction mechanisms in silicon light valves and enhance the flicker accordingly. The major conduction mechanisms of flicker in silicon light valves were residual DC charge on the silicon surface, the voltage holding capability of a liquid crystal cell, the voltage holding capability of a silicon panel, light leakage and parasitic capacitor coupling. Major causes of these flicker mechanisms were identified through systematic characterizations. An empirical model of flicker was proposed with quantitative experimental data and theories. Among these conduction mechanisms, temperature could boost the voltage holding capabilities of a silicon panel to become the most dominant cause of flicker when the temperature was above 40°C. At temperatures below 30°C, the other four conduction mechanisms contributed to the flicker in different ways. Minimization of flicker could be achieved through materials and device optimization.</p
Phase flicker in liquid crystal on silicon devices
No full textThis paper reviews the phase flicker associated with the phase-only liquid crystal on silicon (LCOS) technology. The phase response of the LCOS device often fluctuates with the driving waveforms. Such phase flicker can cause detrimental effect in applications operating on either holographic or non-holographic principles. The origin of the phase flicker and its impact on the performances of various LCOS-based optical systems are explained. Methods to characterise the temporal response of the LCOS device will also be presented. The efforts to reduce the phase flicker in LCOS devices were reviewed. Perspectives on the future directions are also given
Spectral sensitivity of macaque monkeys measured with ERG flicker photometry
No full textThe following is a correction for the article “Spectral
sensitivity of macaque monkeys measured with ERG flicker
photometry,” by Gerald H. Jacobs and Jess F. Deegan
II, that appeared in Visual Neuroscience, 1997,
14, 921–928. As a result of a transcription error
the spectral sensitivity values included in Table 1 were
incorrect.</jats:p
A measurement method for determining the direction of propagation of flicker and for tracing a flicker source
No full textThis paper describes a new and highly efficient measurement method (algorithm) that determines how flicker propagates throughout the network and also traces the dominant flicker source. The fundamental principle of the method is to use the fact that a flicker source produces an amplitude modulation in the voltage and current waveforms. The low frequency variations in voltage and current that cause flicker are retrieved in a demodulation and filtering process. By first multiplying the low frequency variations in voltage and current and then integrate, a new quantity, flicker power, is achieved. The sign and the magnitude of flicker power give the direction to the flicker source as well as tracing the dominating flicker source.Godkänd; 2005; 20081020 (ysko
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