PCD2.M110--1 SAIA 数字信号模块 通信模块

1．合理的结构型式

PCD2.M110--1整体式PLC的每一个L/0点的平均价格比模块式的便宜，且体积相对较小，所以一般用于系统工艺过程较为固定的小型控制系统中﹔而模块式PLC的功能扩展灵活方便·V/点数里﹑输入点数与输出点数的比例、I╱O模块的种类等方面，选择余地较大。维修时只要更换模块﹔判断故啃的范围也很方便。因此比。模块式FLC一般适用于较复杂系统和环境差〈维修里大)的场合。

2.安装方式的选择

根据PLC的安装方式。PCD2.M110--1系统分为集中式、远程V╱O式和多台PLC联网的分布式。集中式不需要设置驱动远程|╱О硬件。系统反应快、成本低。大型系统经常采用远租╱0式，因为它们的奘置分布范围很广，远程)╱O可以分散安装在1╱О装透附近，l╱O连线比集中式的短。PCD2.M110--1但需要增设驱动器和远程l╱O电源。多台联网的分布式适用于多台设备分别独立控制,又要相互联系的场合，可以选用小型PLC，但必须要附加通信模块。

PCD2.M110--1 SAIA大规模控制系统

对于一个自动化工程(特别是中大规模控制系统)来讲，选择网络是很重要的，甚至有人提出了“网络就是控制器”的概念。首先，网络必须是开放的，以方便不同设备的集成及未来系统规模的扩展;其次，PCD2.M110--1针对不同网络层次的传输性能要求来选择网络的形式，这必须在较深入地了解该网络标准的协议、机制的前提下进行;另外，综合考虑系统成本、设备兼容性、现场环境适用性等具体问题，确定不同层次所使用的网络标准。一个实时系统的性能可从时间、可靠性和应用对象三个方面来衡量。

PCD2.M110--1掌握plc扫描原理与其它控制设备比较，PLC最重要的特征是“扫描”。PLC上电后，自动重复执行程序扫描和/O扫描，即输入采样、用户程序执行和输出刷新三个阶段。完成上述三个阶段称作一个扫描周期。在输入采样阶段，PLC以扫描方式依次地读入所有输入状态和数据，并将它们存入/O映象区中相应的单元内，输入采样结束后，转入用户程序执行和输出刷新阶段，即使输入状态和数据发生变化，IV/O映象区中的相应单元的状态和数据也不会改变。在用户程序执行阶段，PLC按由上而下、先左后右的顺序依次地扫描程序（梯形图），根据逻辑运算的结果，刷新RAM存储区或/O映象区对应单元的状态。在输出刷新阶段，根据)/O映象区内对应的状态和数据刷新所有的输出锁存电路，再经输出电路驱动相应的外设，这时，才是PLC的真正输出。可见，PCD2.M110--1采用PLC程序控制的过程和结果与继电器逻辑回路是有区别的，特别是涉及到梯级的次序、脉冲信号的捕捉等，与PLC的扫描原理是密切相关的。实践中，大量的程序问题均源于此，常常会出现不可思议的结果。因此，设计PLC程序，必须精通PLC的基本原理。

PCD2.M110--1 SAIA 数字信号模块 通信模块

1. Reasonable structure type

The average price of each L/0 point of PCD2.M110-1 integral PLC is cheaper than that of the modular type, and the volume is relatively small, so it is generally used in small control systems with fixed system processes; The functional expansion of modular PLC is flexible and convenient. In terms of V/ points, the ratio of input points to output points, and the type of I/O modules, there is a large choice. Only replace the module during maintenance; It is also convenient to judge the scope of the bite. So compare. Modular FLC is generally suitable for more complex systems and poor environment < large maintenance) occasions.

2. Select the installation mode

According to the PLC installation method. The PCD2.M110-1 system is divided into centralized, remote V/O and distributed with multiple PLCS networked. There is no need to set up remote | / ou hardware to drive the centralized system. The system has fast response and low cost. Large systems often use remote lease / 0 because they have a wide distribution range, remote)/O can be scattered around the 1 / O load, and l/O connections are shorter than centralized. PCD2.M110--1 but requires additional drives and remote l/O power supplies. The distributed network of multiple devices is suitable for the independent control of multiple devices and the occasion of mutual contact, you can choose a small PLC, but you must attach a communication module.

PCD2.M110--1 SAIA large-scale control system

For an automation project (especially large-scale control systems), the choice of network is very important, and some people even put forward the concept of "network is the controller". First, the network must be open to facilitate the integration of different devices and the expansion of the system in the future. Secondly, PCD2.M110-1 selects the form of network according to the transmission performance requirements of different network levels, which must be carried out under the premise of a deeper understanding of the protocol and mechanism of the network standard. In addition, comprehensive consideration of system cost, equipment compatibility, field environment applicability and other specific issues to determine the network standards used at different levels. The performance of a real-time system can be measured from three aspects: time, reliability and application object.

PCD2.M110--1 Master the principle of plc scanning Compared with other control devices, the most important feature of PLC is "scanning". After the PLC is powered on, the program scanning and /O scanning are automatically and repeatedly performed, that is, the input sampling, user program execution and output refresh three stages. Completing these three stages is called a scan cycle. In the input sampling stage, PLC reads all the input status and data by scanning, and stores them into the corresponding unit in the /O image area. After the input sampling is over, it is transferred to the user program execution and output refresh stage. Even if the input status and data change, the status and data of the corresponding unit in the IV/O image area will not change. In the execution stage of the user program, the PLC scans the program (ladder diagram) from the top down, first left and then right, and refreshes the state of the corresponding unit in the RAM storage area or /O image area according to the results of logical operations. In the output refresh stage, refresh all the output latch circuits according to the corresponding state and data in the)/O image area, and then drive the corresponding peripheral through the output circuit, at this time, is the real output of the PLC. It can be seen that the process and results controlled by PCD2.M110-1 PLC program are different from the relay logic circuit, especially when it comes to the order of steps and the capture of pulse signals, which are closely related to the scanning principle of PLC. In practice, a large number of procedural problems arise from this, often with incredible results. Therefore, the design of PLC program, must be proficient in the basic principles of PLC.