Siemens touch screen 6AV6643-OCBO1-1AX1

Siemens touch screen 6AV6643-OCBO1-1AX1 Siemens touch screen 6AV6643-OCBO1-1AX1

Xunzhiman Intelligent Control Technology (Shanghai) Co., Ltd. Shanghai Shimu Automation Equipment Co., Ltd

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Figure 1: The main steps of designing and debugging a programmable controller application system

(1) Deeply understand and analyze the process conditions and control requirements of the controlled object

a. The controlled object refers to the controlled mechanical, electrical equipment, production line, or production process.

b. Control requirements mainly refer to the basic methods of control, the actions that should be completed, the composition of automatic work cycles, necessary protection and interlocking, etc. For more complex control systems, the control task can also be divided into several independent parts, which can simplify complexity and facilitate programming and debugging.

(2) Identify I/O devices

Determine the user input and output devices required for the PLC control system based on the functional requirements of the controlled object. Common input devices include buttons, selection switches, travel switches, sensors, etc. Common output devices include relays, contactors, indicator lights, solenoid valves, etc.

(3) Choose the appropriate PLC type

Based on the identified user I/O devices, count the required input and output signal points, select the appropriate PLC type, including model selection, capacity selection, I/O module selection, power module selection, etc.

(4) Allocate I/O points

Assign input and output points to the PLC, prepare an input/output allocation table, or draw a wiring diagram for the input/output terminals. Next, PLC program design can be carried out, and control cabinet or operation console design and on-site construction can also be carried out.

(5) Design application system ladder diagram program

(7) Conduct software testing

After inputting the program into the PLC, testing work should be carried out first. Because there are inevitably omissions in the programming process. Therefore, before connecting the PLC to the on-site equipment, software testing is necessary to eliminate errors in the program and lay a foundation for overall debugging, shortening the overall debugging cycle.

(8) Overall debugging of application system

After the PLC software and hardware design, control cabinet, and on-site construction are completed, the entire system can be debugged online. If the control system is composed of several parts, local debugging should be carried out first, followed by overall debugging; If there are many steps in the control program, segmented debugging can be performed first, and then connected together for overall debugging. The problems discovered during debugging should be eliminated one by one until debugging is successful.

(9) Prepare technical documents

The system technical documents include instructions, electrical schematics, electrical layout diagrams, electrical component lists, and PLC ladder diagrams.

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PLC hardware system design

1. Selection of PLC model

Before making a decision on the system control scheme, it is necessary to have a detailed understanding of the control requirements of the controlled object, in order to decide whether to use PLC for control.

In situations where the logic relationship of the control system is complex (requiring a large number of intermediate relays, time relays, counters, etc.), the process flow and product modification are frequent, data processing and information management are required (including data calculation, analog control, PID regulation, etc.), the system requires high reliability and stability, and preparations are made to achieve factory automation networking, the use of PLC control is necessary.

At present, numerous domestic and foreign manufacturers offer a variety of PLC products with different functions, leaving users confused and at a loss. So, only by comprehensively weighing the pros and cons and making a reasonable choice of aircraft models can we achieve the goal of economic practicality. Generally, the selection of aircraft models should be based on meeting the system's functional needs, and should not be blindly greedy for the bigger picture, in order to avoid wasting investment and equipment resources. The selection of models can be considered from the following aspects.

(1) Selection of input/output points

Blindly selecting models with a high number of points will result in certain waste.

First, clear the total number of I/O points in the control system, and then reserve 15-20% of the actual required total points (leaving room for system modifications, etc.) to determine the required PLC points.

Additionally, it should be noted that some high-density input point modules have limitations on the number of input points that can be connected simultaneously. Generally, the number of input points that can be connected simultaneously should not exceed 60% of the total input points; The driving capability (A/point) of each output point of PLC is also limited, and the magnitude of the output current at each point of some PLCs also varies with the different load voltages applied; The allowable output current of a general PLC decreases with the increase of ambient temperature. Consider these issues when selecting.

The output points of PLC can be divided into common point, grouped, and isolated connections. Different voltage types and voltage levels can be used between isolated output points, but the average price per point of this PLC is relatively high. If isolation is not required between output signals, the PLC with the first two output modes should be selected.

(2) Selection of storage capacity

A rough estimate of user storage capacity can only be made. In a system that only controls switch values, it can be estimated by multiplying the total number of input points by 10 words/point and the total number of output points by 5 words/point; The counter/timer is estimated at (3-5) words per piece; When there is computational processing, estimate based on (5-10) words/quantity; In systems with analog input/output, it can be estimated that each analog input/(or output) requires approximately (80-100) words of storage capacity; Roughly estimate the number of words or more for each interface when there is communication processing. Afterwards, there is usually a margin of 50-100% of the estimated capacity. For inexperienced designers, there should be more margin when choosing capacity.

Design a ladder diagram based on work function diagrams or status flowcharts, which is called programming. This step is the core work of the entire application system design, and it is also a relatively difficult step. To design a good ladder diagram, one must first be very familiar with the control requirements, and also have some practical experience in electrical design.

(6) Input the program into the PLC

When using a simple programmer to input a program into a PLC, it is necessary to first convert the ladder diagram into instruction mnemonics for input. When programming on a computer using auxiliary programming software for programmable controllers, the program can be downloaded to the PLC through the connection cable between the upper and lower computers.