• 전기의세계
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• v.17 no.3
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• pp.29-38
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• 1968

The development of the frequency converter using semiconductor enables to easily control the speed of A.C. motors. It is now technically possible and economically feasible to provide them with power at variable frequency, using silicon-controlled-rectifier (or thyristor) inverters. In such a case, if an induction motor is to be operated efficiently over a wide speed range, it must be supplied from a variable-frequency source whose frequency is adjustable over a range similar to that required for the motor speed. It is desired to observe how several characteristics are changed such as primary current, torque-speed, etc. Although the characteristics could be obtained by means of the conventional method, it requires very complicated calculation. It is assumed that the charateristics above are easily investigated by means of current diagram method from variable circuit constants relating to the motor which is designed in rated frequency. In this paper, the results of the study on the current-diagram method and its application are described as follows; (1) In order to discuss the construction of current diagram, the equation of the stator current with adjustable frequency was derived for applying the Current Diagram Method. (2) The radius, the center of the current circle and current vector locus at any desired frequency could be easily determined with the aid of both above mentioned equation and the standard current diagram at reference frequency. (3) This method could be applicable to the various types of Induction Motors, and this paper has dealt with its application to the capacitor, split-phase and 2-phase types of motors.

• The Journal of the Acoustical Society of Korea
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• v.21 no.3
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• pp.256-263
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• 2002

In this study, the tracking of the temporal variation of the frequency and the amplitude in the presence of additive white Gaussian noise is considered using the Extended Kalman filter (EKF. The EKF has many applications and it has been applied to the problem of tracking the time-variable frequency. However the existing EKF frequency trackers could was driven in the small time-variable amplitude or required the additional amplitude tracker in the large time-variable amplitude. In this study, the EKF frequency-amplitude tracker, which could track both frequency and amplitude simultaneously from the measured signal in the relatively large time-variable amplitude environment, is proposed for improving the performance of the time-variable frequency tracking and its performance is verified by the simulation and the experimental work.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.568-572
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• 2001

An industrial vibratory conveyor system is devised for large-scale feeding by the low-power, using natural frequency of the system. The important thing in this system is to determine the natural frequency and to drive by it. The purpose of this study is to build up reliance on the system with changing of element parameters for vibration characteristics of balancing type vibratory conveyor by using F.E.M. modeling. For investigating the natural frequency, modal testing is performed by using impact hammer, accelerometer and LMS/Vibration Analysis System. Experimental results are compared with F.E.M results. The results of the comparisons within the errors of less than 2 percent can verify the reliability of the F.E.M. analysis of the system. Also we can verify that the characteristics of natural frequency have linearly decreased(-6%) as adding the mass($50{\sim}600kg$). We can find that controlling driving frequency is necessary for triggering the natural frequency, but natural frequency is less affected by adding the mass on the balancing weight.

• International Journal of Air-Conditioning and Refrigeration
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• v.6
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• pp.27-35
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• 1998

An experimental study was performed to investigate the optimum cycle of an inverter heat pump as a function of frequency. The performance of the inverter heat pump with the rated cooling capacity of 4,141 W(3,550kcal/h) was measured with a variation of frequency, indoor and outdoor temperature, and length of capillary tube in the psychrometric test room. As a base case, the inverter heat pump with the standard capillary length of l,000mm(optimum size for the frequency of 60Hz) and ASHRAE Test condition "A" was tested by varying frequency from 30Hz to 80Hz. Then, the optimum cycles were investigated by varying the length of capillary tube at each frequency level of 30, 60 and 80Hz. Based on the experimental data, the change of system characteristics between the optimum and the base case were analyzed for each selected frequency level. Generally, for low frequency level(30Hz), the longer length of the capillary tube compared with the standard size showed the higher energy efficiency ratio(EER), while for high frequency level(80Hz) the shorter length of the capillary tube showed the higher EER.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.1
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• pp.64-72
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• 1997

An experiment study was performed to investigate the optimum cycle of an inverter heat pump as a function of frequency. The performance of the inverter heat pump with the rated cooling capacity of 4141W(3550kcal/h) was measured with a variation of frequency, indoor and outdoor temperature, and length of capillary tube in the psychrometric test room. As a base case, the inverter heat pump with the standard capillary length of 1000mm which was optimum size for the frequency of 60Hz and ARHRAE Test condition A was tested by varying frequency from 30Hz to 80Hz. Then, the optimum cycle was invesigated by varying the length of capillary tube at each frequency levels of 30, 60 and 80Hz. Based on the experimental data, the change of system characteristics between the optimum and the base case were analyzed for each selected frequency levels. Generally, for low frequency level(30Hz), the longer length of the capillary tube compared with the standard size showed the higher EER, while for high frequency level(80Hz) the shorter length of the capillary tube showed the higher EER.

• Journal of Drive and Control
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• v.18 no.1
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• pp.17-23
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• 2021

The flow signal or spool position signal is used to determine the dynamic characteristics of directional control valves. Alternatively, the signal of spool position or flow can be replaced with the velocity of a low friction, low inertia actuator. In this study, the frequency response of the servo valve equipped with a spool position transducer is measured with a metering cylinder. The input signal, spool displacement, load pressure, and velocity of the metering cylinder are measured, and the theoretical results from the transfer function analysis are verified. The superposition rule for magnitude ratio and phase angle was found to be always applicable among any signal type, and it was found that the load pressure signal is not appropriate for use as the signal for measuring the frequency response of a servo valve. It was confirmed that the frequency response of a servo valve using metering cylinder was similar to the results from a spool displacement signal. The metering cylinder used for measuring the frequency response of a servo valve should be designed to have sufficiently greater bandwidth frequency than the bandwidth frequency of the servo valve.

• The Journal of Fisheries Business Administration
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• v.36 no.1 s.67
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• pp.81-101
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• 2005

This article is to estimate the fishing frequency function in Korean recreational fishery with respect to socio-economic characteristics of anglers. First, the study described the characteristics of the entire angler population on the view points of 9 socio-economic variables. And then, the study divided the total angler population into three groups of in-land, sea, and mixed angler populations in order to investigate the differences in their characteristics. The study could confirm the existence of differences in regions, size of regions, and educational levels between the in - land and the sea angler populations by testing heterogeneity in the frequency table. The fishing frequency function is estimated using Poisson regression model in order to accomodate the count data(non-negative discrete random variable) aspects of the fishing frequency. However, the model specification error is found due to overdispersion of data. The model exhibits the lack of goodness of fit. The negative binomial regression model is adopted to cure the overdispersion of the data as an alternative estimation methodology. Finally, the study can confirm overdispersion does not exist in the model any more and the goodness of fit improved significantly to the reasonable level. The results of estimation of fishing frequency population modeled by the negative binomial regression models are following. The three variables of region, sex, and education have effects on the decision making process of fishing frequency in the case of in-land recreation fishery. On the other hand, the three variables of sex, age, and marriage status do the same job in the case of sea angler population. Among the left-over variables, both income and use of Internet variables now affect on the process in mixed angler population. Finally, the results of whole angler population show that all of the previous variables are proven to be statistically significant due to the summation of data with all three sub-groups of angler population.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.7
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• pp.456-461
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• 2015

In this study, the frequency properties of electrostatic capacity and dielectric loss for the samples with different types of filler has been measured in through the applied frequency range of 7 kHz ~3,000 kHz at temperature of $80^{\circ}C$, $110^{\circ}C$, $140^{\circ}C$, $170^{\circ}C$. The results of this study are as follows. When the sample is degradated at the temperature of $80^{\circ}C$, $110^{\circ}C$, $140^{\circ}C$, $170^{\circ}C$ and the frequency range of 7 kHz ~3,000 kHz is applied, It found that the electrostatic capacity of the sample with Polyimide film is larger than the sample with Grass fiber. It found that the dielectric loss for the sample with Polyimide film is larger than the sample with Grass fiber with increasing frequency and temperature in the $80^{\circ}C$, $110^{\circ}C$, $140^{\circ}C$, $170^{\circ}C$ range. Also, the dielectric loss decreased with increasing frequency. In case of the sample with Polyimide film, It found that the electrostatic capacity decreased with increasing temperature, and the dielectric loss gradually decreased with increasing frequency.

• Phonetics and Speech Sciences
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• v.1 no.2
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• pp.129-140
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• 2009

The purpose of the present study is to investigate frequency related information and syllable structure constraints on Sino-Korean. Previous studies on Sino-Korean have mostly investigated the historical change of sounds and reviewed archaic features of Chinese language in Sino-Korean. Unfortunately, there is little study on the sounds of contemporary Sino-Korean in terms of syllable structure constraints. For the purpose of the present study, sounds of 7,742 Chinese characters used in Sino-Korean (7,795 syllables) were investigated and syllable matrices made based on the results of frequency related information. As a result, 483 syllable types were observed and the most frequently observed syllables were as follows: /ku/ (103) > /ki/ (100) > /ju/ (87) > /pi/ (86). Only 16 out of 19 consonants are used for Sino-Korean. /$t^{\ast}$/ and /$p^{\ast}$/ are never used in Sino-Korean and /kh, $s^{\ast}$, $k^{\ast}$/ occur only a few times (3, 2, 1 respectively). /k/ (17.5%) shows the highest frequency and /n, ${\eta}$, 1, tc, m/ occupied the next rankings. Among 20 vowel types, /a/ showed the highest frequency and /o, u, i, $j{\Lambda}$, ${\Lambda}$/ occupied the next rankings. Based on the syllable matrices, gaps were observed and classified into accidental or systematic ones. Onset and nucleus, nucleus and coda, onset and coda, and other syllable structure constraints of Sino-Korean were listed.

• Journal of the Korea Safety Management & Science
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• v.16 no.4
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• pp.305-311
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• 2014

Recently, though it was developed several services using the context-awareness technology of IoT, there exist also obstacles for high quality service. Specifically it is short the study for uncertainty of context-awareness. This study focused on understanding the effect of frequency interference among several environmental factors for location determination to increase precision of location determination. It was found that frequency interference between devices using 2.4Ghz frequency effect on the location determination precision. It was resulted that frequency interference increase the error of location determination precision. Then, we confirmed that it was required the suitable compensation method corresponding to frequency interference.