5SHX0660F0002 plc的选择主要应从机型、容量、i/o模块、电源模块、特殊功能模块、通信联网能力等方面加以综合考虑

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5SHX0660F0002 plc的选择主要应从机型、容量、i/o模块、电源模块、特殊功能模块、通信联网能力等方面加以综合考虑

plc的选择主要应从机型、容量、i/o模块、电源模块、特殊功能模块、通信联网能力等方面加以综合考虑。plc的容量包括i/o点数和用户存储容量两个方面。

　　(一)i/o点数的选择

plc平均的i/o点的价格还比较高，因此应该合理选用plc的i/o点的数量，在满足控制要求的前提下力争使用的i/o点少，但必须留有一定的裕量。

通常i/o点数是根据被控对象的输入、输出信号的实际需要，再加上10%~20%的余量来确定。

　　(二)用户存储容量的选择

用户程序所需的存储容量大小不仅与plc系统的功能有关，而且还与功能实现的方法、程序编写水平有关。一个有经验的程序员和一个初学者，在完成同一复杂功能时，其程序量可能相差25%之多，所以对于初学者应该在存储容量估算时多留裕量。

plc的i/o点数的多少，在很大程序上反映了plc系统的功能要求，因此可在i/o点数确定的基础上，按下式估算存储容量后，再加20%~30%的裕量。存储容量(字节)=开关量i/o点数×10+模拟量i/o通道数×100

另外，在存储容量选择的同时，注意对存储器的类型的选择。

5SHX0660F0002 plc的选择主要应从机型、容量、i/o模块、电源模块、特殊功能模块、通信联网能力等方面加以综合考虑

The selection of plc should be mainly considered from the model, capacity, i/o module, power module, special function module, communication networking capability and other aspects. plc capacity includes i/o points and user storage capacity two aspects.

(A)i/o points selection

The average price of plc i/o points is still relatively high, so the number of plc i/o points should be reasonably selected, and strive to use less i/o points under the premise of meeting the control requirements, but must leave a certain margin.

Usually i/o points are determined according to the actual needs of the input and output signals of the controlled object, plus a margin of 10% to 20%.

(2) The user’s choice of storage capacity

The storage capacity required by the user program is not only related to the function of the plc system, but also related to the method of function realization and the level of program writing. An experienced programmer and a beginner can vary as much as 25 percent in the amount of programs they use to perform the same complex function, so beginners should leave a margin for storage capacity estimates.

The number of plc i/o points reflects the functional requirements of the plc system to a large extent, so it can be determined on the basis of i/o points, and then add 20% to 30% margin after estimating storage capacity according to the following formula. Storage capacity (bytes)= Number of i/o points x 10+ Number of analog i/o channels x 100

In addition, when the storage capacity is selected, pay attention to the selection of the type of storage.