Jo Feb 24, 2023
Wi Ryong Hwan, a researcher at the Faculty of Communications, has developed a device for measuring fault points of cables by a time-digital converter.
Several methods such as TDR, FDR, TFDR, STDR, etc. are used to localize fault points of cables.
The most representative method is TDR. Here, a measurement device emits a pulse and detects the reflecting pulse. It determines a fault point in a cable by calculating time intervals between transmitted and reflected pulses.
With the appearance of a time-digital transformer in recent years, measurement accuracy has been improved significantly. The transformer measures time intervals according to the delay time of CMOS gate and converts time intervals of tens or hundreds of ps into digits.
To develop the device, he used microprocessor PIC16F877 and time-digital transformer GC7820A.
An error of about 0.2 % was achieved for a communication cable of 1 000m.
...
Jo Feb 22, 2023
A research team led by Hong Myong Jin, a section head at the Faculty of Information Science and Technology, has developed a Korean-based integrated management system for broadcasting marine safety warnings to ensure the safety of ships on the seas of our country.
Being a component of the international marine safety system, the system guarantees safe navigation of ships by automatically communicating safety warnings in Korean and English with all the ships up to 250 miles from the coast of our country.
The broadcasting system of marine safety warning (Navtex) is divided into two parts: transmission system and reception system.
The transmission system consists of a transmission antenna at a broadcasting station, a broadcasting transmitter and a control computer.
The control computer is linked with the transmitter by RS-232C port and it controls the transmitter according to the communication protocol. On the computer, messages are written and edited according to Navtex protocol and encoded according to the transmission code converting principle by the integrated management system. The encoded messages are transmitted to ARM processor STM32F103RBT6, CPU of the transmitter, through RS-232C port and transmitted according to the control signals from the computer.
The transmitter consists of CPU, a direct frequency modulator, an output driver unit, an output unit, power unit, etc. CPU in the transmitter controls operation of every unit and transmission processes according to the control program in the internal Flash memory and the control signals from the computer.
STM32F103RBT6 directly controls the frequency modulation and output configurations of the output driver unit using DDS chip of the direct frequency modulator and it transmits acknowledgement signals to the computer. Also, while transmitting data to the direct frequency modulator, it processes the FEC (Forward Error Correction) protocol.
The reception system is made up of receivers on the ships and receivers on base stations (control computers) for broadcasting marine safety warnings.
...
Jo Feb 21, 2023
A research team led by O Hyon Chol, a section head at the Faculty of Heat Engineering, has established a system of providing electricity for stock farms and fuel for cooking in all seasons by producing methane gas from manure and domestic sewage.
The methane gas production system consists of raw material supply system, a residue discharge system, a system for maintaining the temperature of raw material, an agitation system, a filtration system, a power generation system, a waste heat recovery system, a gas supply system for cooking. All these are placed within a greenhouse by solar heat.
They analyzed the defects revealed during methane gas production at the existing production plants in operation, and conducted a calculation of heat to maintain temperature in winter. On the basis of this, they reinforced the fermentation tank to minimize heat loss and established a system which recovers waste heat from the engine for heating raw material to keep the fermentation temperature at 30℃ to 35℃. It is the waste heat exchanger that recovers waste heat from a methane gas engine. It provides heat necessary for the fermentation tank but has no influence on normal operation of the engine.
Thus, they managed to provide methane gas of 80 to 100m3 in a 100m3 tank, which produced 30~45kWh of power and fuel for cooking every day.
As all the processes in the system such as supply and discharge of raw material, stirring of raw material, cleaning of gas and power generation needs only one person, it is simple in operation and has little operation cost and failure. It is very useful because methane gas can be produced without additional investment as long as there are domestic animals.
The system can satisfy power demands at stock farms and provide heat for cooking without burning any coal. Besides, it can prevent environmental pollution from manure and produce good organic fertilizer to contribute to agricultural production.
...
Jo Feb 20, 2023
A research team led by Choe Chol Min, a researcher at the Faculty of Electronics, has developed a real-time ozone meter to measure ozone concentration at disinfection stations and transmit measured values to the control board of an ozone generator through RS-485(Modbus RTU).
In general, several methods such as chemical titration, spectrophotometry, ultraviolet absorption, chemical luminescence, chemical fluorescence and electrochemical analysis are used for measurement of ozone concentration.
Electrochemical analysis is based on the Faraday's law which explains that current generated from electrochemical reduction of ozone at a work electrode inside a sensor is proportional to the concentration of ozone.
The meter based on electrochemical analysis is composed of a sensing circuit, a filtering and amplifying circuit, a communication circuit, a display circuit, a power source stabilizing circuit and a microprocessor.
At disinfection stations, ozone meters are affected by a strong electromagnetic field from several pieces of electronic equipment such as an ozone generator. In other words, sensing signals are affected by several high frequency noises as well as the source noise and this leads to a big error in the measured value without elimination of the noise. As sensing signals are DC signals, they eliminated the source and high frequency noises with the help of a low-pass filter. In order to prevent the effect of cable resistance and cable noise on the signals, they designed the meter so that they could be converted into 1kHz signals and transmitted to the meter.
They built two communication circuits in the meter. One is a communication circuit which uses V-F conversion to prevent the attenuation of sensing signals in case of the distance of more than 30m between the meter and the sensor. The other one is RS-485 circuit which transmits measured values to the control board. The main circuit and the source circuit are separated from each other, which ensures the stability of the communication circuit.
They also wrote a program to display exact values of ozone concentration and CT and to transmit CT values to the control board by RS-485(Modbus RTU).
The characteristics of the developed meter are as follows.
Measurement index: ozone concentration, CT
Measurement range: 0~200ppm
Relative error: below 5%FS
Relative standard deviation: below 2% (n=11)
...
Jo Feb 18, 2023
Recently, under the increasing ecological awareness and stringent regulations for marine environmental protection, we often meet vessels in which stern tube water-lubricated plastic bearings are applied to the propulsion shafting.
It is because plastic bearings offer simplicity, low initial and operating costs, and no risk of oil pollution, compared with oil-lubricated white metal bearings or water-lubricated rubber bearings.
A research team led by Kim Chun Il, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has developed a water-lubricated stern bearing with plastic material.
First, they conducted a test on the suitable composition of plastic sliding bearings and their characteristics. Then, they determined the lubrication characteristics of stern tube plastic bearings such as the allowable load capacity of bearings, the stiffness and damping coefficients of water lubricating films, and the maximum allowable radial clearance of bearings.
The friction coefficient (against brass) is 0.003 and the dilatation (radial direction) is 0.005.
Compared with a stern tube rubber bearing, the load capacity is raised by 1.2 times and the lifetime is prolonged by 1.5 times thanks to the smaller value of frictional coefficient and higher breaking-in capacity. In addition, it results in the reduction in initial cost by one fifth and in labour and time by one third as it needs no non-ferrous metal and natural rubber.
...
Jo Feb 16, 2023
Choe Chol Min, a researcher at the Faculty of Electronics, has developed a portable photocolorimetric ozone meter for regular calibration of a real-time ozone meter at disinfection stations, based on indigo carmine spectrophotometry.
Ozone disinfection process needs both correct real-time measurement of ozone concentration at disinfection stations and regular calibration of ozone meters.
All over the world, indigo carmine spectrophotometry is the choice of the standard method for measurement of ozone concentration and it is being widely used for the air and ozone generators.
The photocolorimetric ozone meter is based on Lambert-Beer’s law, which explains that absorbance is proportional to the concentration of chemical sorts absorbing the light when a solution absorbs the light of given wavelength and the thickness of the solution layer is fixed.
The photocolorimetric ozone meter consists of a driving circuit for light source, a light detection circuit, a filtering and amplifing circuit, a source supply stabilizing circuit and a microprocessor.
The driving circuit for light source contains a constant-current source circuit to stabilize the maximum of light source brightness. The light source driving current can be changed from 0mA to 22mA. For exact driving current, an operational amplifier AD8602 with 80㎶ of input bias voltage, 0.2pA of bias current, and 80dB of PSRR is used in the constant-current source circuit.
In the light detection circuit, higher accuracy of measurement is provided by the difference in the light intensity from the light source (I0) and that passed through the sample (I). Here, a low noise operational amplifier OPA111 is used.
The technical characteristics of the device are as follows.
Measuring range: 0~200ppm
Relative error: Less than 0.4%FS
Relative standard deviation: Less than 1% (n=11)
At persent, the meter is in wide use at several disinfection stations.
...
