• Progress in Superconductivity and Cryogenics
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• v.5 no.1
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• pp.111-117
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• 2003

In the design of the split type free displacer Stilting cryocooler the motion of the displacer is very important to decide the cooling capacity, which depends upon the working gas pressure, the swept volume in the compression space and the expansion space, operating frequency, the phase shift between piston and displacer, etc. In this study, Stirling cryocooler actuated by the electric farce of the dual linear motor is designed and manufactured. Cool down characteristics of the cold end with laser displacement sensor in the expander of the Stilting cryocooler is evaluated. The charging pressure was 15kg$_{f}$/$\textrm{cm}^2$ and operating frequency was 50Hz. Input power and the lowest temperature were about 32W and 67K, respectively. And, displacement of the piston is measured by LVDTs (Linear Variable Differential Transformers), displacement of thedisplacer is measured by laser optic method, and phase shift between piston and displacer is discussed. As the peak-to-peak pressure of the compressor was increased, peak-to-peak displacement of the displacer was increased. The peak-to-peak displacement of the displacer increases in the range of 0 - 64.5Hz(resonant frequency of the displacer), but decreases steeply when the operating frequency is bigger than the resonant frequency. Finally when the phase shift between displacements of the Piston and displacer is 45。, operating frequency is optimum and is decided by resonant frequency of the expander, mass and cross section area of the displacer and constant by friction and flow resistance.e.

• Journal of the Korea Institute of Military Science and Technology
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• v.26 no.1
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• pp.1-9
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• 2023

The skin structure of sensor pod mounted on the exterior of aircraft can be exposed to the acoustic dynamic load and static load such as aerodynamic pressure and inertial load during flight. Fatigue life prediction of structural model under acoustic load should be performed and also differential stiffness of model modified by static load should be considered. The acoustic noise test spectrum of MIL-STD-810G was applied to the structural model and the stress response power spectral density (PSD) was calculated. The frequency response analysis was performed with or without prestress induced by inplane static load, and the response spectrum was compared. Time series data was generated using the calculated PSD, and the time and frequency domain fatigue life were predicted and compared. The variation of stress response spectrum due to static load and predicted fatigue life according to the different structural model considering mean stress were examined and decreasing fatigue life was observed in the model with prestress of compressive static load.

• Korean Journal of Food Science and Technology
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• v.29 no.6
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• pp.1119-1124
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• 1997

This study was carried out for improvement and correction of the traditional pressure variation method (PVM) in the respiration rate measurements of fresh fruits and vegetables using a microcomputer system and a differential pressure sensor. Water vapor pressure in the container was calculated by equations for psychrometric calculations. At the beginning of experimental period water vapor pressure in the container was increased and maintained constantly in the most experimental period, but was decreased dramatically after $CO_2$ scrubbing. The percentages of water vapor pressure on total differential pressure were $33{\sim}46%$ at $1^{\circ}C$, $23{\sim}45%$ at $11^{circ}C$ and $35{\sim}53%$ at $21^{\circ}C$. The differences between the respiration rates determined by gas chromatography and corrected pressure variation method (CPVM) were $0.2{\sim}0.3\;mgCO_2kg^{-1}h^{-1}$ at $1^{\circ}C$, $0.2{\sim}2.9\;mgCO_2kg^{-1}h^{-1}$ at $11^{\circ}C$ and 1.0{\sim}9.0\;mgCO_2kg^{-1}h^{-1}$ at $21^{circ}C$, while those between gas chromatography and normal pressure variation method (PVM) were $0.8{\sim}1.2\;mgCO_2kg^{-1}h^{-1}$ at $1^{\circ}C$, $3.9{\sim}11.0\;mgCO_2kg^{-1}h^{-1}$ at $11^{\circ}C$ and $8.0{\sim}32.0\;mgCO_2kg^{-1}h^{-1}$ at $21^{circ}C$, respectively. The differences of the respiration rates with CPVM were smaller than those with PVM. CPVM, therefore, were more exact and convenient method than PVM in the measurement of respiration rate of fresh produce.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1867-1869
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• 2003

In this paper, chamber(Circuit breaker compartment of C-GIS) made of stainless steel with 4 mm width is used. Artificial defect was made on enclosure or HV conductor of chamber and $SF_6$ gas was injected into it according to pressure. In this experiment, Acoustic emission sensors of different types was used to compare sensitivity to detect acoustic signal occurred by Partial discharge(PD) of according to types and resonance frequency in $SF_6$ gas atmosphere. Sensors used in tests was R6I, R15I and 2/4/6 Pre-Amplifier connected with R6IU without pre. amp. In case of R6IU, gain was adjusted with 40 dB like other sensors and operated by differential mode. Post amplifier(post. amp) and band pass filter(BPF) were developed Gain of post. amp. is 60 dB and BPF has band width of $50{\sim}300$ kHz. Also, envelope circuit developed reduces frequency of AE sensor. As a result, in $SF_6$ atmosphere, R6IU and R6I had resonance frequency of 60 Hz was better than R15I. Also, R6IU was better than R6I because of type property of pre.amp. had differential mode.

• Journal of Sensor Science and Technology
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• v.23 no.5
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• pp.326-331
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• 2014

In this study, a MEMS microphone that uses $Si_3N_4$ as the vibration membrane was produced for application as an auditory device using a sound visualization technique (sound visualization) for the hearing impaired. Two sheets of 6-inch silicon wafer were each fabricated into a vibration membrane and back plate, after which, wafer bonding was performed. A certain amount of charge was created between the bonded vibration membrane and the back plate electrodes, and a MEMS microphone that functioned through the capacitive method that uses change in such charge was fabricated. In order to evaluate the characteristics of the prepared MEMS microphone, the frequency flatness, frequency response, properties of phase between samples, and directivity according to the direction of sound source were analyzed. The MEMS microphone showed excellent flatness per frequency in the audio frequency (100 Hz-10 kHz) and a high response of at least -42 dB (sound pressure level). Further, a stable differential phase between the samples of within -3 dB was observed between 100 Hz-6 kHz. In particular, excellent omnidirectional properties were demonstrated in the frequency range of 125 Hz-4 kHz.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.10
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• pp.687-696
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• 2010

In this study, FDD algorithm was developed using the normalized distance method and general pattern classifier method that can be applied to constant air volume air handling unit(CAV AHU) system. The simulation model using TRNSYS and EES was developed in order to obtain characteristic data of CAV AHU system under the normal and the faulty operation. Sensitivity analysis of fault detection was carried out with respect to fault progress. When differential pressure of mixed air filter increased by more than about 105 pascal, FDD algorithm was able to detect the fault. The return air temperature is very important measurement parameter controlling cooling capacity. Therefore, it is important to detect measurement error of the return air temperature. Measurement error of the return air temperature sensor can be detected at below $1.2^{\circ}C$ by FDD algorithm. FDD algorithm developed in this study was found to indicate each failure modes accurately.

• Journal of the Korean Society of Hazard Mitigation
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• v.6 no.4 s.23
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• pp.15-20
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• 2006

This study developed integration control system that improve efficiency and give flexibility of smoke control system and can improve prevention of disasters performance. The reliable each kind sensor and of integration control system was developed by establishing the specifications, algorithms and constructing engineering data. More correct and reliable control function of optimization can be obtained by the central control from integration control system rather than the existent individual control. This sees to do to impose flexibility to smoke control system. Also, this will provide the basics of integration control system and ability security of smoke control system and can construct smoke control system of performance based.

• Journal of Sensor Science and Technology
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• v.27 no.6
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• pp.380-385
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• 2018

Recently, interest in baseball has been increasing as the level of international baseball games, the popularity of domestic leagues, and the number of players entering the MLB has increased. In this paper, we propose a pitching system that can be applied to both professional and amateur baseball. The pitching system consists of a control module using MSB764T PLC, a pitching mechanism including AC motors and a ball feed rail, an HMI using the CHA-070WR model, inverter, etc. To pitch the breaking balls, the two AC motors each use an inverter to independently control the speed. The implemented pitching system was experimented on, investigating ball speed and ball movement according to RPM using the BUSHNELL Velocity Speed Gun. Experimental results on ball speed are similar to the theoretical data and the measured data. From the experimental data, it is confirmed that the damping coefficient value for the pitching ball is about 0.98. In the case of the breaking ball, the larger the difference between the speeds on the sides of the ball and the faster the ball speed, the larger the bending degree.

• Journal of the Korean GEO-environmental Society
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• v.14 no.3
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• pp.51-60
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• 2013

It is proposed the new method to calculate the absolute altitude and horizontal position of worker in construction field. For this research, we used a pressure sensor, MEMS INS sensor to acquire 3D position of worker. The easiest way to show the result of this research is to use smart phone which equipped various digital sensors in this hardware. So we made two softwares: Data acquisition software in Android smart phone and Data monitoring software in PC. During this research, we encountered several kind of problems which have to be overcame. This paper shows these processes and the results of 3D positioning technologies we suggested newly.

• Journal of Korea Society of Industrial Information Systems
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• v.28 no.6
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• pp.21-27
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• 2023

Modern naval ships install an Infra-Red Signature Suppression system (IRSS) in their exhaust pipe to reduce infrared signature emitted to the outside. In addition, naval ships are strategic assets with a very long life cycle, so high reliability of the performance of the equipment on board must be guaranteed. Therefore, equipment such as IRSS is evaluated for performance through model testing at the design stage. A variety of measuring instruments are used in IRSS model testing, and the reliability of these instruments must also be guaranteed. In this paper, a study was conducted to evaluate the reliability of measurement equipment used in IRSS model testing. The test equipment and instruments used were a hot gas wind tunnel, pitot tube, digital differential pressure gauge, thermocouple sensor, and digital recorder. As the fan speed of the hot gas wind tunnel increased, the measurement deviation of the flow decreased, and the temperature output of the thermocouple sensor showed differences in response time and stability depending on the method used.