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PLC system integration
Time:2015-01-14

PLC system integration project is mainly applied at locations where only limited points are to be monitored and controlled. Such as:

•1、Monitoring project implemented in tank farm.

•2、Monitoring and control system implemented on mid-split unit

•3、Monitor, control and interlock protection carried out on small unit

•4、Field data collection RTU is required in case of distant application

•5、Process control of special craftwork coal delivery system

Composition, function and requirement of PLC system

Structure

The structure for PLC only can be described as monolithic construction or modular construction.

The average price for each I/O point for PLC with monolithic construction is cheaper than that of modular construction type. The dimension for PLC with monolithic structure is smaller than that of PLC with modular construction. PLC with monolithic construction is mainly applied in small-scale control system where there is little change on system process flow. While PLC with modular construction is more convenient and flexible in terms of function expansion. The selection of I/O point number and the selection of the ratio of input point number to output point number are more flexible. It is more convenient for you to carry out maintenance work. It is usually applied in more intricate control system.

(2) Mounting means

The installation of PLC can be described as centralized installation, remote I/O and multiple PLC being distributed in a wide area and linked via network.

As for centralized installation, the hardware used for driving remote I/O can be saved. So, this type of system boasts characteristic of fast response and low cost; Remote I/O mode is suitable for large scale system. Equipment in this type of

system can be scattered over a large area. PLC with remote I/O construction can be installed near field facilities. So, connection cable used by PLC is very short. But, this type of installation needs new driver and remote I/O power supply;

The last type of installation is ideal for application where multiple equipments are controlled independently and interconnection between them is required, small PLC can be used, but additional communication module is needed.

(3) Relevant functions of PLC system

Generally speaking, small (low-grade) PLC boasts functions such as Boolean calculation, timing and counting, which can be applied in situations where only switching signal is needed.

For control system where switching signal control is predominant and a few analog signal control is needed, you can choose enhanced and Low-grade PLC in which A/D and D/A are equipped, plus-minus calculation and data transmission function are included.

For control system where functions such as PID calculation, close-loop control and network communication are required, you can choose middlings or high-grade PLC, depending on scale of the system.

(4) Requirement on response time for PLC system

PLC is a general controller specially developed for industry automation design. Response speed for PLC in different level can meet application requirement. If you have special requirement on response speed of some function or signal, careful consideration should be made on PLC response speed. You can choose the type of PLC which boasts high speed I/O process function, or the type of PLC which possesses fast response module and interrupt input module.

(5) Requirement on PLC system reliability

Generally speaking, the reliability of PLC can meet application demand. As for control system which requires very high reliability, You can choose redundant system or thermal standby system.

(6) Procedure used for selection of PLC capacity

PLC capacity includes I/O point number and memory space reserved for customer.

(A) selection on I/O number

The average price for I/O point of PLC is quite expensive. So it is necessary to choose the number of I/O point properly. I/O point number should be as fewer as possible under the precondition that control demand can be met and proper margin has been considered.

Generally speaking, the number selection of PLC I/O points should based on actual need of the object to be controlled, and with the consideration of margin of 10% to 15%.

Selection of memory space

The memory space required by user not only depends on the function of PLC, but also depends on method used in realizing the function and the knowledge level of programmer.