AB PLC防通讯中断技术

针对AB PLC通讯中断,介绍AB PLC通讯中断后的具体现象,对造成PLC通讯中断的干扰源进行详细的分析,阐述这些干扰源对PLC进行干扰的主要途径,介绍外界干扰的计算方法,提出解决AB PLC通讯中断的措施和具体方案,说明在程序上怎样解决这一干扰问题,给出通讯中断诊断系统程序的编辑思路和编辑方法,同时用逻辑顺序图描述通讯中断诊断系统的程序扫描过程,提高了整个电控系统的稳定性和安全性,取得满意的效果.     

施耐德上位机服务器通讯中断问题的研究和改进

通过对泰钢1~#高炉上位机监控服务器使用过程中遇到的通讯中断故障进行研究,提出在设计和维护使用过程中必须注意和采取的切实可行的对策措施。消除通讯中断问题,从而避免网络异常的发生,为同类故障的解决提供了参考。     

PROFIBUS DP现场总线常见故障分析

PROFIBUSDP现场总线运行一段时间后,经常出现通讯中断或某些子站报通讯故障。分析认为是通讯电缆太长导致信号衰减、DP通讯头阻值过小、电磁干扰和接地等原因所致,采用加装中继器,重新敷设通讯电缆,确保接地良好等措施,保证了通讯网路正常。     

实时多任务操作系统Z80—RTOS的设计

本文以建立在Z80 CPU上的小型实时多任务操作系统Z80-RTOS为例,介绍小型实时多任务操作系统的设计原理和实现方法,并较全面地叙述Z80-RTOS的四个功能(即任务调度、任务控制、任务通讯及中断管理)的实现及算法、数据结构的选择。     

通讯中断的分析和处理

本文分析了酒钢炼钢二工序计算机系统通讯中断产生的原因,采取有效措施,逐步完善系统,取得了良好的效果。     

OPC客户端应用程序的开发

针对Intouch监控系统实际运行过程中遇到的死机现象,数据通信遇到障碍,使得上层应用软件的数据通讯中断.本文开发了OPC SERVER和SQL SERVER之间的OPC客户端应用程序,此程序与Intouch并行通信,采集数据,实现实时数据的通讯,从而解决了数据通讯中断的问题.     

MasterNet控制网络缺陷分析

基于MasterNet的技术分析,讨论网络节点故障处理时导致生产中断的原因,发现MasterNet控制网络存在设计缺陷.结果表明,对AS515采用冗余配置可避免重启节点对生产的影响;ACA50死机或进程死锁可通过短暂停产重新启动;更换GCOM通讯板需要全线停产,并按固定顺序启动所有MasterNet的网络节点.     

铝电解整流机组监控通讯优化与应用

本文探讨了铝电解500kA电解铝大功率整流机组稳流控制PLC在大磁场的工业环境中运行过程中存在的PLC通讯中断、数据丢失、机组短暂性失控问题,对问题进行浅析并提出优化改进措施。     

传动控制中光纤通讯的优越性

针对传动控制中主从控制的实时性问题进行研究,分析了利用PROFIBUS通讯、DSL通讯和光纤通讯实现主从控制时,光纤通讯的优越性。设计出光纤通讯为基础的主从控制下,ABB的DCS800装置的硬件组成和参数设计。     

UCOMM测控自动化系统在变电站综保系统改造中的应用

分析了南钢总降变电站综合自动化系统存在的问题,使用UCOMM系统制定了进行改造的过程与步骤,有效解决了通讯中断与数据丢失的问题,确定了系统稳定运行。     

Closed-Form Solutions for Vibrations of Nearly Vertical Strings and Beams by Means of Asymptotic Methods

Top tensioned strings and beams are often used in civil and marine applications. Typically these members have constant cross sections, and a pronounced, usually linear, tension variation, due to the effects of gravity. In this paper simple, approximate formulas for the natural frequency of such strings are derived, based on asymptotic techniques, while for the tensioned beam case approximate closed-form results are developed by the Wentzel–Kramers–Brillouin method. Both derivations are shown in reasonable detail. While similar work is known for a beam with varying axial tension this is believed to be the first time that a single analytic expression is developed for the full length of the beam. A simple example in which the bottom tension is only 9% of the top tension is analyzed for cases with and without bending stiffness, and the solutions have been compared to the exact solution for the string case and to the results from three finite-element programs for the beam case. The accuracy was found to be very good, even in this situation, in which the tension variation is large.     

Comparison of Settling-Velocity-Based Formulas for Threshold of Sediment Motion

The critical condition for incipient sediment motion is formulated in this note based on the settling velocity. The formula obtained is simple, relating the ratio of critical shear velocity to settling velocity to the dimensionless sediment diameter. Comparisons are then made with other settling-velocity based formulas available in the literature. To facilitate the computation of the effective near-bed velocity at the threshold condition, a generalized law-of-the-wall function is proposed for predicting the velocity distribution under various boundary conditions. This study demonstrates that the settling velocity is equivalent to the critical near-bed velocity, which is experienced by a typical bed sediment particle under the threshold condition, but only for large sediment sizes such as sand and gravel. Comparison results show that Yang’s formula is suitable for flows with small flow depth relative to sediment size while Le Roux’s formula may overestimate the threshold condition for fine particles by up to 30%.     

Role of midwives

Dr. Alfano (New England Journal of Medicine 296: 1126, 1977) is certainly entitled to his personal opinions, but when they appear in a major publication in a setting that calls for factual information, they cannot go unchallenged. Midwives have played and continue to play a major part in maternal-infant services in many advanced European countries. Combined midwife-physician services in Sweden, Finland, Japan, Netherlands, Denmark, Norway, and Switzerland produced infant mortality rates in 1972 superior to those reported by Dr. Alfano for the Commonwealth of Massachusetts in 1974. Even in 1967 Sweden and the Netherlands (where most infants are delivered by midwives) had infant mortality rates, respectively, of 12.9 and 13.4/100 live births. These numbers, of course, do not mean that midwives are superior to doctors, but they do not seem to prove them inferior when they are employed in an appropriate setting. In Oregon (where certified nurse-midwives have been employed for some years) the professional midwife is found mainly in the "expensive" practices, so that if there is a "3rd-level of care," it is delivered to the well-to-do rather than the indigent. It is a little early to tell, but the impression around here is that although the quality of the birth experience may be changed by addition of midwives to an upper-middle-class practice, the outcome in terms of numbers of live babies is no different. This finding may not apply when 1 is dealing with the economically disadvantaged. A striking study from California demonstrated a definite improvement in fetal outcome when certified midwives were added to an established program and a tendency for the infant mortality rate to rise again when their services were discontinued for lack of funds. A similar program is under way in Oregon, but it is much too early for results to be apparent. This letter is not written in defense of midwives - it is a plea for balance and rationality. Medicine is no place for a territorial imperative. Only by calling on the expertise of all qualified members of a society can one hope to progress and to improve the human condition.     

Effects of acetyl CoA on the pre-steady-state kinetics of the biotin carboxylation reaction of pyruvate carboxylase

The approach to steady-state for the formation of the enzyme-carboxybiotin complex obeys first-order kinetics, with the proportion of the total enzyme present as the enzyme-carboxybiotin complex in the steady-state being about 60%. The approach to steady-state for ATP cleavage also obeys first-order kinetics. The apparent first-order rate constants for the approach to steady-state, in the presence and absence of acetyl CoA, respectively, are 6.6 and 0.028 s(-1) for ATP cleavage and 6.1 and 0.028 s(-1) for enzyme-carboxybiotin formation. The similarities of the values of the rate constants for the two reactions indicates that there is a common rate-limiting step. The large enhancement of these rate constants in the presence of acetyl CoA suggests that a major effect of acetyl CoA in the reaction is to enhance the rate of the step in which the putative carboxyphosphate complex is formed and in which ATP is cleaved. In addition, in the presence of acetyl CoA, the formation of the enzyme-carboxybiotin complex is much more tightly coupled to ATP cleavage in the presence of acetyl CoA than in its absence. Modeling studies were performed, and reaction schemes are proposed which give simulations similar to the experimental data. In the reaction schemes, the carboxyphosphate intermediate is able to undergo abortive decomposition without carboxylating biotin. The rate of this abortive reaction is greatly reduced in the presence of acetyl CoA.     

CMS探测技术及Surpac软件在矿山损贫指标分析中的应用

应用充填采矿法进行矿石回采的矿山在进行损失贫化计算过程中,有时需要了解采空区的实际体积,因此必要的采空区测量手段就显得尤为重要。以果洛龙洼矿区3 840～3 854 m分段试验采场为研究对象,应用CMS探测技术对试验采场采空区进行扫描并利用Surpac软件进行后处理,最终计算得出试验采场的采矿损失率为2.76%,矿石贫化率为22.08%,与设计损贫指标估算值较为吻合,对指导矿山后期矿石回采具有一定的现实意义。     

The Rule of Equivalent States in Limit-State Analysis of Soils

Soil is typically regarded as a frictional or cohesive-frictional material in limit-state considerations. Often the solution to a limit-state problem (for instance, the bearing capacity of footings) for a purely frictional soil is easier to obtain than the solution for a cohesive-frictional material. A theorem was presented that makes it possible to obtain a solution for cohesive-frictional soil through a transformation of a known solution for purely frictional soil. However, application of the transformation rule based on this theorem is shown to have limitations. This rule appears to be applicable for boundary-value problems where boundary stresses have only normal components and principal stress trajectories are not altered by the transformation. With modern computational tools the correspondence rule is bypassed. However, its applicability is a consequential issue in soil mechanics education, even if of a somewhat historical nature. An example of limit loads on a strip footing is presented, a solution to inclination coefficients is produced, and the consequences of the rule of corresponding states are discussed. Finally, the application of the rule of correspondence in the kinematic approach of limit analysis is investigated. A convenient method is developed for calculations of the energy dissipation rate, which does not require tedious calculations of dissipation on all velocity discontinuity surfaces or in continually deforming regions.     

Prediction of reoxidation inclusion composition in casting of steel

A model is developed to calculate the composition of reoxidation inclusions that form during pouring of steel castings. The software package Thermo-Calc is used to obtain the inclusion phase fractions and compositions as a function of the temperature and oxygen content of the steel. Oxygen is assumed to be continually absorbed by the steel until the liquidus temperature is reached. Both lever rule and Scheil-type analyses are performed. The model is applied to reoxidation of two carbon steels, one low-alloy steel and one high-alloy steel. The effects of variations in the steel composition and the oxygen absorption rate on the inclusion composition are investigated in a parametric study. The mass fraction of absorbed oxygen is determined by matching predicted with previously measured reoxidation inclusion compositions for the various steels. Good agreement is obtained for most phases present in the inclusions. Interestingly, the agreement in the inclusion compositions occurs for all steel grades when the percentage of absorbed oxygen is equal to 0.9 wt pct. This value is explained using a separate model for the rate of oxygen absorption at the steel-atmosphere interface. Various scenarios are outlined that allow for the 0.9 wt pct of absorbed oxygen to be achieved. The model is then used to calculate the amount of alloy elements consumed and inclusions formed as a function of the oxygen boundary layer thickness in the atmosphere and the integrated free surface area of the liquid steel during pouring. It is found that for unprotected liquid steel transfer operations, such as tapping and ladle filling, the integrated free surface area and exposure time product can reach values of the order of 100 m²s per ton of steel, and that the air-to-steel volume ratio during pouring can be as large as 40. It is concluded that, in order to create a comprehensive tool for simulating reoxidation formation, more detailed models are needed for the external oxygen transfer in the atmosphere, the flow of the liquid steel during pouring, and the internal transport and reactions of chemical species in the steel.     

The Development of Ring Rolling Technology

A thorough survey of work on ring rolling published in the English and German languages by 2004 is presented. The process is briefly introduced and a set of ideals are stated, as the target for all developments in the area. The main challenges which inhibit attainment of these ideals are given, and the process is compared with alternatives. The main body of the review is organised in four parts: the evolution of the design of ring rolling equipment is described, including detailed discussion of the design and manufacture of preforms; the methods used to investigate the process are reviewed, separated into experimental and theoretical categories; the insights gained from these investigations are organised according to the challenges identified at the outset; developments in the control and operation of the process are described. Having given a set of ideal targets for the process, the state of current knowledge about ring rolling is assessed in order to predict likely developments: process modelling capability is nearly able to predict rolling behaviour for a complete cycle with sufficient accuracy to allow effective use of models for design of rolling schedules and preforms; analysis of material behaviour is relatively mature for steel rings, but has scope for significant extension for titanium and aluminium alloys and composites; design choices that seek to extend the flexibility of the process have had some exploration, but could be extended. Finally, the seminal contribution of Professor Kopp is briefly described.     

规划模型在黄金矿山长远规划中的应用

黄金矿山是资源型企业，企业的生存、发展与延续是资源型企业的共同问题。在现有资源条件下，如何进行矿床的最优化开采始终是矿山的一条主线。焦家金矿已经基本到了生产的中后期，此时矿床的优化开采就显得尤为重要。文中对焦家金矿的现有储量作了统一规划，建立了矿山的年计划和供矿区段的优化配矿开采模型，并进行了优化求解，排出了年进度计划，为矿山中后期的矿床优化开采提供了依据。