Papers by Keyword: Frequency Modulation

Abstract: The paper introduces a system using PLL frequency modulation and demodulation technique, and using infrared as the carrier to realize wireless communication. CD4046 is a common CMOS low-frequency phase locked loopintegrated circuit, and it has the characteristics of high VCOlinearity, tunable center frequency and acquisition frequency range, low power consumption and simple for use. The paper introduces the design scheme using the technique for infrared communication, and proposes a method using sing-chip microcontroller to control single channel to realize the simultaneous transmission of acoustic signal and digital signal, which has great practicability.

Abstract: The advantages of fiber optic sensors in contrast to conventional electrical ones make them popular in different applications. In the field of strength of materials, structure curvature is an important parameter. The limitations of traditional curvature measurement technology and the characters of fiber optic sensors are analyzed. The research status and characters of curvature measurement of different type fiber optic sensors are introduced. Potential and some successful applications of fiber optic sensors in high voltage switching are presented. It is reasonable to believe that the fiber optic sensing technology is a hot research topic in high voltage equipment fields for next a long time.

Abstract: Traditional frequency power and test equipment cannot meet the requirements. This paper discusses in detail the composition of FM type series resonance test device, technical principles, characteristics and advantages. And also introduces wiring method, test methods, test standard. The instance proves that discharge test of large transformer using the FM series resonance device is convenient and accurate.

Abstract: The introduction of the direct digital frequency synthesis (DDS) technology in the field of communication is against the traditional ultrasonic machining power supply which does not have the multi-frequency tracking shortcomings to build a frequency conversion type ultrasonic power. Frequency conversion type ultrasonic power supply is based on DSP embedded system and adopts direct digital frequency synthesis (DDS) technology combined with a software phase locked frequency of composite frequency tracking scheme to realize automatic search transducer resonance frequency and frequency automatic tracking function which can response the different characteristics of the transducer dynamical; With the use of phase shift control power-principle to realize the output power regulating function when the frequency changes and reduce the switching power loss; It provides an important reference for the design of new frequency conversion type ultrasonic power.

Abstract: Rolling-element bearings have been used in the engineering practice since the very beginning of the XIX century. The scientific literature on the subject is therefore rich. As rotational speeds of bearing shafts were getting higher, new problems appeared. Quite a new challenge to be faced were turbine engines with very high rotational speeds that considerably augmented both the scope of problems and the demand for fast and reliable diagnostic methods. The FDM-A diagnostic method (FM frequency modulation, D direct current, C - the level of the methods advancement) has been based on measurements of frequency modulation of the component of pulsation whereas the FAM-C method (FM frequency modulation, C alternating current, C - the level of the methods advancement, i.e. applications in the form of an automatic tester are in use) has been based on measurements of the alternating-current frequency. Both the methods have been developed at ITWL (Air Force Institute of Technology), Warsaw, Poland. Accuracy of these methods essentially results from the natural synchronization of the sampling signal with the angular velocity of kinematic links under examination. The methods enable abrasive wear of a given subassembly to be determined and localised in the course of the power plants regular operation. Possible is determination of numerous parameters of the bearings themselves, the bearing nodes, and the rotating (compressor-turbine) assembly, just to mention the degree of the rolling friction for any of the bearings, the smoothness of motion of the bearing cage, sizes of radial clearances, the level of abrasive wear of contact surfaces of both the bearing cage and the rolling element. A diagnostic unit is fitted to any item, e.g. an electrical joint, supplied with DC or AC voltage. What has been presented in the paper is findings from the performance testing of the aircraft turbine engine: the role of the generator observer has been played by a DC generator and a three-phase tachogenerator.

Abstract: The optical current transformer is an important content in smart grid research field. When the Faraday DC optical measurement system was used in DC current measurement, the low frequency noise caused by photo detector and measured signal were overlapped, which makes the measuring accuracy decrease. To solve this problem, the noise of photo detector is analyzed. Then, the frequency modulation is proposed for spectrum shifting. Furthermore, the principle of modulation method is deduced in formula, and the characteristics of deferent frequency are also analyzed. On this base, modulation signal source is designed. With LabVIEW program, the signal from modulation source is acquainted and analyzed. The results show that this modulation method can realize spectrum shifting and the designed signal source is able to generate waveform needed.

Abstract: This paper reports on direct frequency modulation of a RF Colpitts oscillator, realised from silicon carbide devices and proprietary components, capable of transmitting sensor data whilst operating at 300°C. Utilizing a reversed biased Schottky diode as a varactor in an LC oscillator, it is possible to modulate the frequency of an RF carrier by applying external voltage signals. These experiments have shown that a 10V bias will increase the frequency by as much as 10%, however signals as low as 10mV are easily detectable with standard silicon receivers.

Abstract: In this paper, an interface for low-Q micromachined gyroscope is designed. Based on the testified system architecture, the driving circuit with frequency modulation and PI controller, together with the sensing circuit contained twice demodulation, are designed. The bias stability of the gyroscope is 0.072 o/s, and the noise is 0.02o/s/Hz1/2.

Abstract: Closed-loop driving circuit is widely used in the high performance micrimachined gyroscope. But in the capacitive micromachined gyroscope, this circuit can be self-oscillation incapability because of signal coupling by parasitical capacitance. A novel closed-loop driving circuit based on the frequency modulation method is present in this paper. Since the frequency of driving signal is modulated, it is different from the frequency of sensing current. Even if there is coupling, the phase requirement of closed-loop driving method is not destroyed, which overcomes the disadvantage of self-oscillation incapability. Both the simulations and test results are provided, which demonstrates the feasibility of this method.

Abstract: The FDM-A diagnostic method [2, 4] based on a frequency modulation measurement of a pulsation component as well as the FAM-C method of an alternating current frequency have been elaborated in Air Force Institute of Technology. These methods to define a level of an assembly abrasive wear as well as its localization during a normal work of a power unit. A diagnostic signal is derived from onboard generators or alternators. Each damaged part of the generator’s or alternator’s power unit is a vibration generator or modulator. The vibration is turned into oscillation in onboard generators or alternators. After many years of the FAM-C and FDM-A methods’ using it is possible to localize and define value of many faults of power units: a coupling eccentricity, a shaft skew, extender longitudinal clearances of turbine engine’s rotor assembly, a frictional resistance of bearings, a smoothness of bearing’s rolling and a bearing cage, a break of rolling bearing’s separator, a misalignment of a rotor assembly’s support, etc. In FAM-C and FDM-A methods two kinds of presentations are used: first a presentation as characteristic patterns (analogous to Fourier spectrum lines but providing to observe periodical and stochastical phenomena) as well as the presentation of the frequency versus time. From the point of view of authors in many cases they are similar to presentations known from a theory of a radio signals transmission. It is possible to find carrier wale and side spectrum lines, beats caused by summation of two signals with approximate frequencies as well as many others. If analogy is so univocal, it is possible to use many systems and dependences used in telecommunication. For example: coherence demodulation (synchronous), which authors intend to use for separation characteristic patterns of two different mechanical assemblies with approximate vibration frequencies. At the end there are presented authors’ considerations, related to superposition of signals and beats as well as reflection of these phenomena in observed power units.