Rise time

About: Rise time is a research topic. Over the lifetime, 4748 publications have been published within this topic receiving 47512 citations.

Pulse width modulation simulator for testing insulating materials

Abstract: A test instrument for testing magnet wire which is provided which tests, collects and permits analyzing the effect of temperature, frequency, voltage and rise time associated with magnet wire use, and more particularly, the effects of those variables on the insulation of the wire, so as to evaluate the magnet wire performance and inverter controlled dynamoelectric machine applications.

Modeling of heat generated on stress grading coatings of motors fed by multilevel drives

Abstract: Stress grading (SG) coatings used in high voltage rotating machines are considerably affected when the machines are controlled by adjustable speed drives. In some applications the SG coatings are subjected not only to voltage components of high frequency associated with the switching devices used by the drive but also to a component of the fundamental frequency above 100 Hz. In this work, the heat generated on SG coatings under multi-level PWM waveforms is studied. The effect of the fundamental frequency, rise time, switching frequency and number of voltage levels, on the resistive heat generation is computed by using a circuit model implemented in PSCAD/EMTDC, which takes into account the nonlinear behavior of the material. According to the results, with a PWM waveform, the average heat density increases with the fundamental frequency, but this increment is considerably smaller than that expected with a pure sinusoidal waveform. Also the simulation results show how a reduction of the average resistive heat in the stress grading coating can be expected as the rise time of the pulses is increased by means of a suitable dV/dt filter. However, the effect of changes on the fundamental frequency or rise time of the pulses on the average heat is less significant compared to the changes in the switching frequency, one of the features of more influence on the heat generation. An increment in the number of levels of the PWM waveform produces a significant reduction in the average heat. With a 5 level configuration the resistive heating becomes similar in magnitude and distribution to the one produced by a pure sinusoidal voltage waveform.

Transient temperature performance of an integrated micro-thermal system

Abstract: A novel integrated thermal microsystem was designed and fabricated with a heater, microchannels and distributed temperature sensors. This device allows, for the first time, an experimental study of the transient behavior of a thermal microsystem. The transient temperature behavior of the device was studied for a variety of heater power levels and forced convection flow rates, where DI water was used as the working fluid. Both heating-up rise time and cooling-down fall time due to a step current input were determined for natural and forced convection heat transfer. The transient temperature response to a sinusoidal power input was also investigated. The resulting temperature distribution was measured as a function of the input signal and the flow rate. The step response under natural convection is exponential for both heating and cooling processes. However, under forced convection, the heating-up time response exhibits a clear overshoot. The response time for both heating and cooling process is about four times faster than that for the natural convection case. Furthermore, under certain conditions, the periodic temperature response can exhibit a large peak-peak temperature without the occurrence of dry-out phenomenon.

DOI Determination by Rise Time Discrimination in Single-Ended Readout for TOF PET Imaging

Abstract: Clinical TOF PET systems achieve detection efficiency using thick crystals, typically of thickness 2-3 cm. The resulting dispersion in interaction depths degrades spatial resolution for increasing radial positions due to parallax error. Furthermore, interaction depth dispersion results in time pickoff dispersion and thus in degraded timing resolution, and is therefore of added concern in TOF scanners. Using fast signal digitization, we characterize the timing performance, pulse shape and light output of LaBr3:Ce, CeBr3 and LYSO. Coincidence timing resolution is shown to degrade by ~50 ps/cm for scintillator pixels of constant cross section and increasing length. By controlling irradiation depth in a scintillator pixel, we show that DOI-dependence of time pickoff is a significant factor in the loss of timing performance in thick detectors. Using the correlated DOI-dependence of time pickoff and charge collection, we apply a charge-based correction to the time pickoff, obtaining improved coincidence timing resolution of <; 200 ps for a uniform 4 × 4 × 30 mm3 LaBr3 pixel. In order to obtain both DOI identification and improved timing resolution, we design a two layer LaBr3[5%Ce]/LaBr3[30%Ce] detector of total size 4 × 4 × 30 mm3, exploiting the dependence of scintillator rise time on [Ce] in LaBr3:Ce . Using signal rise time to determine interaction layer, excellent interaction layer discrimination is achieved, while maintaining coincidence timing resolution of <; 250 ps and energy resolution <; 7% using a R4998 PMT. Excellent layer separation and timing performance is measured with several other commercially-available TOF photodetectors, demonstrating the practicality of this design. These results indicate the feasibility of rise time discrimination as a technique for measuring event DOI while maintaining sensitivity, timing and energy performance, in a well-known detector architecture.

Time Resolution Performance Studies of Contemporary High Speed Photomultipliers

Abstract: The time resolution capabilities of prototype microchannel plate and static crossedfield photomultipliers have been investigated. Measurements were made of electron transit time, rise time, time response, single photoelectron time spread and multiphotoelectron time spread for LEP HR350 proximity focused high gain curved microchannel plate and VPM-154A/1.6L static crossed-field photomultipliers. The experimental data have been compared with results obtained with conventionally designed RCA 8850 and C31024 high speed photomultipliers. Descriptions are given of both the measuring techniques and the measuring systems.