外文翻译--底土的土壤结构和饱和导水率

《外文翻译--底土的土壤结构和饱和导水率》由会员分享，可在线阅读，更多相关《外文翻译--底土的土壤结构和饱和导水率（11页珍藏版）》请在毕设资料网上搜索。

1、英文原文 ： Low-cost programmable pulse generator for particle telescope calibration Abstract In this paper we present a new calibration system for particle telescopes including multi pulse generator and digital controller. The calibration system generates synchronized pulses of variable height for every

2、 detector channel on the telescope. The control system is based on a commercial microcontroller linked to a personal computer through an RS-232 bidirectional line. The aim of the device is to perform laboratory calibration of multi-detector telescopes prior to calibration at accelerator. This task i

3、ncludes evaluation of linearity and resolution of each detector channel, as well as coincidence logic. The heights of the pulses sent to the detectors are obtained by Monte Carlo simulation of telescope response to a particle flux of any desired geometry and composition. Elsevier Science B.V. All ri

4、ghts reserved. To assure a correct interpretation of data obtained with scientific instruments onboard satellites, as well as to compare these data with those of similar instruments, a thorough pre-flight calibration is required. For solar and cosmic ray particle telescopes, this calibration is usua

5、lly carried out in two steps: first, a calibration of each individual detector using radioactive sources and standard nuclear instrumentation (NIM or CAMAC modules),following by a final test of the whole telescope performed in a particle accelerator site. The success of calibration on accelerator re

6、quires that, prior to the experiences, all detectors and electronics parameter (polarization voltages, amplifier gains and shaping times, thresholds, etc.) have nearly definitive values. Here we propose a cheap and simple pre-calibration procedure based on a new system that we have called Programmab

7、le Pulse Generator (PPG). The PPG developed in our laboratory has been designed for a specific instrument, a four-detector cosmic ray telescope, but it can easily be modified for similar experiments. The standard calibration procedure for individual detectors and their electronic chains consists of

8、introducing pulses of known amplitudes coming from a pulse generator, together with the pulses released in the detector by particles coming from a radioactive source. However, these standard pulse generators do present several limitations: The pulse amplitude must be set manually. Thus, to generate

9、the pulses that different particles with different energies would release on the detectors, it is necessary to change the pulse heights every time. Standard pulse generators only provide one output signal, so either several modules are needed to calibrate a complete telescope, or it is necessary to

10、split the single output in order to get several signals. It is difficult to check the coincidence logic because the four signals are not independent. To overcome these difficulties, pulse generators of programmable amplitude and rate have been proposed. Abdel-Aal 1presented a programmable random pul

11、se generator where the height and separation of individual pulses are controlled by software.But in his scheme the pulses are released directly from a digital-to-analog converter(DAC),thus having the temporal characteristics of the DAC output. Our purpose is to generate variable height analog pulses

12、 with similar shape to that released by nuclear detectors. The low-cost PPG presented here is intended to introduce every detector channel ， the pulses released by any particle flux supposed to be encountered by the instrument on real experiments (in our case, on outer space environment). The propos

13、ed pre-calibration scheme is sketched in the diagram of Fig 1. For a big number of simulated events, the energy signals released at the different detectors of the telescope are stored on a personal computer (PC). For each individual event, the energy signal data are sent through a bidirectional RS-2

14、32-C line to the PPG, which transforms the results of the simulation into real pulses and sends them to the real instrument. Fig 1 2 PPG description The design of the PPG is divided into two functional modules: digital electronics and analog electronics, whose block diagrams are enclosed in dashed b

15、oxes shown in Fig2. The data arriving at the digital module from the PC are sent to 12 bit DAC. The DAC output voltages are transformed in the analog module into suitable pulses, ready to be introduced into the test input of the related detector channel of the telescope. Analog and digital modules a

16、re described with some detail in Sections 2.1 and 2.2. In Section 2.3 we describe some noise problems related with the microcontroller, and the way we found to solve them. 2.1 Analog module This module must be capable of producing signal pulses similar to those generated in the detectors by the pass

17、age of energetic charged particles, whose shape can be described by the following function: V t e x p e x p .1/R F R FA t t (1) The relevant signal parameters are the pulse height or amplitude A, the rise time R and the fall time F (here expressed as 1/e times rather than 10-90% times). Using semico

18、nductor detectors, typical values for R and F are approximately 5 ns and 10 us, respectively. Our particular telescope has four detectors, therefore four almost simultaneous pulses with different amplitudes 14AA have to be generated for each simulated event. These amplitudes are sent by the digital

19、module to the analog module, together with a start pulse (see Fig 2). The communication is performed through a coupler circuit for isolation purposes. The start signal is sent to a reference pulse generator, which generates a pulse of constant amplitude, rise and fall times. One of the inputs of each multiplier is this reference pulse, and the other is one of the DAC amplitude signals. Thus, every multiplier acts as a modulator: when the reference pulse arrives,