Papers by Keyword: Time Constant

Abstract: According to the problem of dynamic calibration of the thermocouple, especially impossible to evaluate the rise time and to unify the calibration method, a new method of thermocouple calibration is proposed. Based on the method rise time of the input signal of thermocouple and step amplitude could evaluate accurately. The practical process of calibration shows that the method is effective.

Abstract: Our previous work presented a method for estimating the time constant of grinding system in infeed period. To monitor the precision cylindrical plunge grinding process in dwell period, an estimation of the time constant of grinding system in the dwell period, using acoustic emission signal, is presented in this paper. Acoustic emission signals generated during precision grinding are sensitivity and present challenges for accurate and reliable process monitoring. Experiments demonstrate the results of the acoustic emission sensing approach in estimating the time constant in the dwell period of cylindrical plunge grinding.

Abstract: To monitor the precision cylindrical grinding process, an estimation of the time constant of grinding system, using acoustic emission signal, is presented during infeed period in this paper. Acoustic emission signals generated during precision grinding are sensitivity and present challenges for accurate and reliable process monitoring. Experiments demonstrate the results of the acoustic emission sensing approach in estimating the time constant. This estimation of the time constant can be used to analyze the properties of mechanical materials of the workpiece with the same grinding conditions.

Abstract: The dynamic characteristics of temperature sensor are very important in industrial temperature measure. In this paper, the dynamic characteristics of temperature sensor of AD590 has been researched on the same step volume and different initial temperature, and the different step volume and the same initial temperature, and in the state of the protected pipes and unprotected pipes by combining the theoretical model and many experimental data. Based on the theory of dynamic characteristics of sensor, a large number of experiment data was analyzed and compared, the time constant τ was obtained, also we discussed the relationship between the time constant and the amount of the step, and predicted the mathematical model and analyzed the main factors that affecting the dynamic characteristics of temperature sensor.

Abstract: In order to investigate the influence of the traps which exist in the multi-quantum-well (MQW) of GaN-based light-emitting diodes (LEDs), we analyzed the output current fluctuation known as random telegraph noise (RTN) at reverse-biased region. We could find the two-level current fluctuations at two samples (S1, S2) and the low-level average time (τlow) is larger than the high-level average time (τhigh) at both samples, which means that the energy level of the trap is located below the mid-gap of used material. With increasing a reverse bias voltage, in case of S1, τhigh becomes higher and τlow becomes lower as the energy level of the trap becomes relatively higher in reference to quasi Fermi level, EFn. On the contrary, the τhigh becomes lower and the τlow becomes higher at S2 as the energy level of the trap becomes relatively lower in reference to quasi Fermi level, EFp.

Abstract: PID controller has already been applied widely, but it is difficult to meet the requirement of both static and dynamic performance, which makes PID running without efficiency. Through programming transition process, the paper designs the rationality of given signals in the whole process and introduces an auxiliary application of differential signals, which can realize the control goal in programming control process and make the control key change from confirming the transition of system model to estimating the constant time of system roughly, and the control effect has been improved evidently. By analyzing MATLAB simulation, the paper verifies that the algorithm is reasonable and prevalent.

Abstract: A metal-oxide-semiconductor (MOS) capacitor was fabricated using 4H-SiC epitaxial layer, and the interface state was evaluated in oxygen and hydrogen ambient under high-temperature conditions by the AC conductance technique. The relationships between interface state density (Dit), and corresponding time constant (tit) were obtained. Influences of oxide thickness and of gate metal (Pt or Al) were studied. Dit of Pt gate capacitor is influenced by ambient gas at higher temperature but Dit of Al gate capacitor is little affected by ambient gas. Dit of capacitor with thicker oxide layer tends to be lower than that of capacitor with thinner oxide layer. Interface states with larger time constant are decreased for hydrogen ambient comparing with oxygen ambient in the Pt gate capacitor.

Abstract: Matching of pulse plasma generators to various gas discharges for surface treatment of materials depends on plasma processing equipment. In order to investigate the influence of pulse plasma generator and gas discharge parameters on electrical signal waveforms during the process of unipolar pulse plasma nitriding, equivalent electrical circuit was introduced. The influence of parasitic inductance of interconnection lines and vacuum chamber physical properties was also included in the given equivalent circuit. Gas discharge characteristics at different process parameters were investigated. It was found that the gas discharge and pulse plasma generator properties, as well as the electrical characteristics of interconnecting lines determined the system electrical signal response. From the analysis of optical signals emitted by the gas discharge it was found that the optical signal response might be represented by a typical RC integrator circuit response with the time constant higher than that of the equivalent electrical circuit of generator load. The conclusion was drawn that the process of charge particles generation is followed by the process of active species generation responsible for thermo-chemical processes on the cathode surface. Thus, the increase of the pulse plasma frequency is limited by the thermo-chemical process efficiency, and not only by the generator switching characteristics or by gas discharge electrical properties.