基于CDT2000 I/O口的A/D转换系统设计

为实现传感器数据快速、高精度地转换,提出了一种采用AD7891芯片的A/D转换系统的设计方法。数据读、写和并行工作时序通过CDT2000 I/O口控制,CDT2000 I/O口的电位变化由PC/104通过总线操作。在AD7891与CDT2000之间添加JK触发器实现对A/D转换完成的识别。试验结果表明,这种方法能够满足数据采集系统的设计要求,并且在硬件上较容易实现。     

A/D、D/A转换电路的发展趋势

A/D、D/A转换电路是模拟集成电路的重要组成部分,具有广泛的应用领域。本文介绍了这些转换电路的国内外发展概况,关键制造技术,今后的发展趋势。比较了A/D和D/A转換器的各种类型的特点和应用范围,提出了目前科研和市场的典型产品和参数水平。     

基于石英挠性加速度计A/D与I/F数据采集系统的对比研究

为满足对寻北仪导航系统中加速度计采集数据的高精度要求,提出了基于石英挠性加速度计的A/D采集系统与I/F数据采集系统的对比研究;系统采用了高精度A/D转换芯片AD7693和V/F高精度转换芯片LM331分别对石英挠性加速度计采集的数据进行处理转换,以FPGA芯片XC7Z020为逻辑控制核心对转换的数据进行编帧处理,通过RS232总线将处理的数据发送到上位机;测试结果表明,在相同条件下,I/F采集系统转换的精度99.99％优于A/D采集系统转换的精度98.7％;短时间内,I/F采集系统采集的数据变化不大,A/D采集系统采集的数据变化大,所以I/F采集系统稳定性更好.     

放电能量密度对NTP-SCR系统降低柴油机NOX排放的影响

放电能量密度对NO_X转换效率具有直接影响,传统方法选取的放电能量密度在NO_X转换上,转换效率较低,严重影响柴油机NO_X的排放。因此,以试验的方式研究了放电能量密度对NTP-SCR系统降低柴油机NO_X排放的影响。制备催化剂,以常柴4FCTCI柴油机、测功机、内燃机测控系统、NTP-SCR系统、流量计、气体采样管和柴油机排气分析测试设备构成实验平台,在该实验平台上,研究不同放电能量密度下,NO_X的转换效率。试验结果表明,在放电能量密度过低或过高时,NO_X的转换效率都较低,而在放电能量密度为60J/L时,NO_X转换效率最高。并通过仿真实验的方式,证明应用此次研究的放电能量密度后NO_X的转换效率比应用传统方法的NO_X的转换效率高,说明此次试验得到的放电能量密度值是有效的,可提高NO_X转换效率,以降低柴油机NO_X排放,在柴油机排气后处理领域有着广泛的应用前景...     

采用具有反馈回路的A/D转换方法提高A/D转换的分辨率

指出了提高 A/ D转换分辨率的现有技术及其存在的问题。提出了一个具有反馈回路的A/ D转换方法 ,用以有效地提高 A/ D转换的分辨率。给出了一个应用实例     

用AD650作APPLE-Ⅱ的A/D转换接口电路

<正> 一、前言电压/频率转换技术是实现模拟量到数字量转换的一种方法。采用V/F 转换芯片实现A/D 转换,价格低廉,精度高,线路简单,在速度要求不高的情况下     

提高A/D转换精度的设计思想及实现电路

研究、分析了测量过程中的A/D转换精度问题 ,得出了使用低位A/D转换器获得和高位A/D转换器相当的转换精度的设计思想及实现电路     

A/D转换器外围电路设计

在微机采样测试系统中,模拟量的采样,通常由 A/D 转换芯片完成。市场上有产品的 A/D 转换接口板可供选择,但一般价格较昂贵,对专业的微机化系统设计者,常须自行设计。首先根据测试结果精度的要求选定 A/D 转换器型号,此后,主要的工作就是围绕 A/D 转换芯片设计满足 A/D 转换器正常工作要求的外围电路。     

特殊数/模转换器件AD390的应用

介绍一种具有特殊应用的D/A转换芯片AD390,该芯片性能优越、使用简便、构成的系统结构紧凑、占用印制板面积小,在许多D/A应用场合是理想的转换芯片.     

基于FPGA的串行A/D转换模块设计

使用了基于FPGA的Xilinx公司Spartan-3E系列的XC3S250ETQG144处理器, 对A/D转换芯片TLC549进行驱动采样和后续实际电压值读取. 采用Verilog语言, 整个模块设计在ISE的环境下进行, 设计时减少复杂逻辑, 精简模块设计, 实现高速A/D转换和时序控制, 该设计可移植性强, 利用ISE进行编译、综合、仿真, 为后续A/D转换的工作提供了实验依据. 实验表明设计可靠性高, 可以满足A/D转换的高精度、实时性、抗干扰等方面的要求.     

M/G/c/K blocking probability models and system performance

An exact solution for the M/G/c/K model is only possible for special cases, such as exponential service, a single server, or no waiting room at all. Instead of basing the approximation on an infinite capacity queue as is often the case, an approximation based on a closed-form expression derivable from the finite capacity exponential queue is presented. Properties of the closed-form expression along with its use in approximating the blocking probability of M/G/c/K systems are discussed. Extensive experiments are provided to test and verify the efficacy of our approximate results.     

设计模式变体的描述与验证*

为解决标准设计模式演化后难以检测的问题,引入设计模式变体思想,以Bridge模式为例,给出了八种常用的变体实现,并以人工形式挖掘了四种开源系统中Bridge模式变体的基准数,接着在Apache Ant1.6.2与JHotDraw5.1开源系统中通过六种主流设计模式检测工具进行了变体检测实验。试验结果表明,FCA-CBR方法简单有效,对2种开源系统中Bridge模式变体检测的精确率达到60%与48.1%,与先前方法相比有了较大的提高。     

(r∞, n12, s12) measurements on the 2-CPU CRAY X-MP

We report performance measurements made on the 2-CPU CRAY X-MP at ECMWF, Reading. Vector (SIMD) performance on one CPU is interpreted by the two parameters ($\text{r}{}_{\mathrm{\infty }}\text{, n}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$), and we find for dyadic operations using FORTRAN $\text{r}{}_{\mathrm{\infty }}\text{= 70}\text{Mflop/s}\text{, n}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 53}\text{flop}$. All vector triadic operations produce $\text{r}{}_{\mathrm{\infty }}\text{= 107}\text{Mflop/s}\text{, n}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 45}\text{flop}$; and a triadic operation with two vectors and one scalar gives r_∞ = 148 Mflop/s and $\text{n}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 60}\text{flop}$. MIMD performance using both CPUs on one job is interpreted with the two parameters ($\text{r}{}_{\mathrm{\infty }}\text{, s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$), where $\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ is the amount of arithmetic that could have been done during the time taken to synchronize the two CPUs. We find, for dyadic operations using the TSKSTART and TSKWAIT synchronization primitives, that r_∞ = 130 Mflop/s and $\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 5700}\text{flop}$. This means that a job must contain more than ～ 6000 floating-point operations if it is to run at more than 50% of the maximum performance when split between both CPUs by this method. Less expensive synchronization methods using LOCKS and EVENTS reduces $\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ to 4000 flop and 2000 flop respectively. A simplified form of LOCK synchronization written in CAL code further reduces $\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ to 220 flop. This is probably the minimum possible value for synchronization overhead on the CRAY X-MP.     

Geom/G/1/n system with LIFO discipline without interrupts and constrained total amount of customers

Consideration was given to the discrete-time queuing system with inversive servicing without interrupts, second-order geometrical arrivals, arbitrary (discrete) distribution of the customer length, and finite buffer. Each arriving customer has length and random volume. The total volume of the customers sojourning in the system is bounded by some value. Formulas of the stationary state probabilities and stationary distribution of the time of customer sojourn in the system were established.     

Complex random sample scheduling and its application to an N/M/F/Fmax problem

“Complex Random Sample Scheduling(CRSS)” was proposed in this paper as an efficient heuristic method for solving any permutation scheduling problems. To show the effectiveness of the proposed CRSS, it was applied to an N-job, M-machine, permutation flowshop scheduling problem to minimize makespan, N/M/F/F_max. Numerical experiments made it clear that the proposed CRSS provides a schedule very close to the near-optimal schedule obtained by the existing promising heuristic methods such as taboo search and simulated annealing, within less computation time than these heuristic methods.     

Efficient implementation of Johnson''s rule for the n/2/F/Fmax scheduling problem

Several efficient algorithms of O(n log n) computational complexity, for the Johnson's rule to schedule a set of simultaneously available jobs on two machines in a flowship to minimize the maximum job flowtime have appeared in the literature. A modified version of one of these algorithms is presented which not only simplifies the programming effort for implementation but is also able to generate all possible optimal sequences obtainable from Johnson's rule.     

On the M/Ck/1 queue

We obtain the exact analytic expression of the probability distribution of the number of units in a single server queue with Poisson arrivals and Coxian service time distribution (notated as M/C_k/1). A recursive procedure for calculating this probability distribution is given. The well-known queues M/E_k/1 and M/D/1 are re-derived as special cases of the M/C_k/1 queue. Finally, the cases of M/C₂/1 and M/C₃/1 are fully worked out.