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What hardware does Rockwell ABPLC consist of?
Rockwell AB The hardware of the PLC is mainly composed of a central processing unit (CPU), a memory, an input unit, an output unit, a communication interface, and an expansion interface power supply. Among them, the CPU is the core of the PLC, and the input unit and output unit are interface circuits that connect field input / output devices and the CPU. The communication interface is used to connect with peripherals such as programmers and higher-level computers.
For the integral PLC, all components are installed in the same chassis, and its composition block diagram is shown in Figure 1. For the modular PLC, each component is independently packaged into modules, and each module is connected by a bus and installed on a rack or rail. Its composition block diagram is shown as in Fig. 2. No matter which type of structure PLC, it can be configured and combined according to user needs.
Although the structure of the integral type and modular PLC is not the same, the functions and functions of each part are the same. The main components of the PLC are briefly introduced below.
1. Central Processing Unit (CPU)
Like ordinary microcomputers, the CPU is the core of the PLC. The CPUs configured in the PLC are different and different. There are three common types: general-purpose microprocessors (such as Z80, 8086, 80286, etc.), single-chip microprocessors (such as 8031, 8096, etc.) and bit-chip microprocessors (such as AMD29W, etc.). Most small PLCs use 8-bit general-purpose microprocessors and single-chip microprocessors; medium-sized PLCs mostly use 16-bit general-purpose microprocessors or single-chip microprocessors; large-scale PLCs mostly use high-speed bit-chip microprocessors.
At present, small PLCs are single CPU systems, while medium and large PLCs are mostly dual CPU systems, and even some PLCs have up to 8 CPUs. For a dual-CPU system, generally one is a word processor, generally using an 8-bit or 16-bit processor; the other is a bit processor, using a special chip designed and manufactured by each manufacturer. The word processor is the main processor, which is used to perform programmer interface functions, monitor internal timers, monitor scan time, process byte instructions, and control the system bus and bit processors. The bit processor is a slave processor, which is mainly used to process bit operation instructions and realize the conversion of PLC programming language to machine language. The use of a bit processor increases the speed of the PLC and enables the PLC to better meet real-time control requirements.
In the PLC, according to the functions given by the system program, the CPU directs the PLC to work in an orderly manner. In summary, there are the following aspects:
1) Receive the user program and data input from the programmer.
2) Diagnose the working faults of the power supply, PLC internal circuits, and syntax errors in programming.
3) Receive the status or data of the scene through the input interface and store it in the input image register or data register.
4) Read the user program one by one from the memory and execute it after interpretation.
5) According to the result of the execution, update the status of the flag bit and the content of the output image register, and realize output control through the output unit. Some PLCs also have functions such as tabular printing or data communication.
There are two main types of memory: one is a random access memory RAM for read / write operations, and the other is a read-only memory ROM, PROM, EPROM, and EEPROM. In PLC, the memory is mainly used to store system programs, user programs and work data.
The system program is written by the PLC manufacturer and is related to the hardware composition of the PLC. It completes system diagnostics, command interpretation, function subroutine call management, logic operation, communication, and various parameter settings, and provides a platform for PLC operation. The system program is related to the performance of the PLC, and it will not change during the use of the PLC. Therefore, it is directly fixed in the ROM, PROM or EPROM by the manufacturer, and the user cannot access and modify it.
The user program is determined by the control object of the PLC, and is an application program prepared by the user according to the control requirements of the production process of the object. In order to facilitate reading, inspection and modification, user programs are generally stored in CMOS static RAM, and lithium batteries are used as a backup power source to ensure that information will not be lost when power is lost. In order to prevent interference from damaging the program in the RAM, when the user program runs normally and does not need to be changed, it can be solidified in the read-only memory EPROM. Many PLCs now use EEPROM directly as user memory.
Working data is some data that is frequently changed and frequently accessed during PLC operation. Stored in RAM to meet the requirements of random access. In the working data memory of the PLC, there are storage areas for storing logical devices such as input and output relays, auxiliary relays, timers, and counters. The status of these devices is determined by the initial settings and operating conditions of the user program. According to requirements, some data is backed up by a backup battery to maintain its current state when power is lost. This part of the storage area where data can be saved when power is lost is called the hold data area.
Because the system program and work data have no direct contact with the user, the form and capacity of the memory listed in the PLC product sample or user manual refers to the user program memory. When the capacity of the user memory provided by the PLC is insufficient, many PLCs also provide memory expansion functions.
3． Input / output unit
The input / output unit is usually also called I / O unit or I / O module, which is the connection part between PLC and industrial production site. The PLC can detect various data of the controlled object through the input interface, and use these data as the basis for the PLC to control the controlled object. At the same time, the PLC sends the processing result to the controlled object through the output interface to achieve the control purpose.
Because the signal levels required by external input devices and output devices are diverse, and the information processed by the PLC's internal CPU can only be standard levels, the I / O interface must implement this conversion. I / O interfaces generally have photoelectric isolation and filtering functions to improve the anti-interference ability of PLC. In addition, there are usually status indicators on the I / O interface. The working status is intuitive and easy to maintain.
The PLC provides I / O interfaces with various operating levels and driving capabilities. There are various I / O interfaces for users to choose from. The main types of I / O interfaces are: digital (switching) input, digital (switching) output, analog input, analog output, etc.
There are three types of common digital input interfaces according to the power they use: DC input interface, AC input interface, and AC / DC input interface.
a) DC input b) AC input c) AC / DC input
There are three types of commonly used switch output interfaces according to different output switching devices: relay output, transistor output, and bidirectional thyristor output. The basic principle circuit is shown in Figure 4. The relay output interface can drive AC or DC loads, but its response time is long and the operating frequency is low; while the transistor output and bidirectional thyristor output interface have fast response speed and high operating frequency, but the former can only be used to drive DC loads, the latter is only Can be used for AC loads.
a) Relay output b) Transistor output c) Thyristor output
The number of input signals and output signals that the PLC's I / O interface can accept is called the number of PLC input / output (I / O) points. The number of I / O points is one of the important basis for choosing PLC. When the system's I / O points are insufficient, the system can be expanded through the PLC's I / O expansion interface.
4． Communication Interface
The PLC is equipped with various communication interfaces, and these communication interfaces generally have a communication processor. PLC can communicate with monitors, printers, other PLCs, computers and other equipment through these communication interfaces. The PLC is connected to a printer to output and print process information, system parameters, etc .; it is connected to a monitor to display control process images; connected to other PLCs, it can form a multi-machine system or be connected to a network to achieve larger-scale control. Connected with a computer, it can form a multi-level distributed control system to realize the combination of control and management.
The remote I / O system must also be equipped with the corresponding communication interface module.
5. Intelligent interface module
The intelligent interface module is an independent computer system, which has its own CPU, system program, memory, and interfaces connected to the PLC system bus. As a module of the PLC system, it is connected to the PLC through the bus for data exchange and works independently under the coordination and management of the PLC.
There are many types of PLC intelligent interface modules, such as high-speed counting modules, closed-loop control modules, motion control modules, and interrupt control modules.
6. Programming device
The function of the programming device is to edit, debug, and enter user programs. It can also monitor the internal status and parameters of the PLC and conduct man-machine dialogue with the PLC. It is an indispensable tool for developing, applying and maintaining PLC. The programming device may be a dedicated programmer or a general-purpose computer system equipped with a dedicated programming software package. The special programmer is produced by the PLC manufacturer. ** Some PLC products produced by this manufacturer are used. It is mainly composed of keyboard, display and external memory sockets. There are two types of special programmers: simple programmer and intelligent programmer.
The simple programmer can only be programmed online, and it cannot directly input and edit the ladder program. You need to convert the ladder program into an instruction list program to enter it. The simple programmer is small in size and cheap in price. It can be directly plugged into the programming socket of the PLC or connected to the PLC with a special cable to facilitate programming and debugging. Some simple programmers have storage boxes that can be used to store user programs, such as Mitsubishi's FX-20P-E simple programmer.
Intelligent programmer is also called graphic programmer. In essence, it is a dedicated portable computer, such as Mitsubishi's GP-80FX-E intelligent programmer. It can be programmed both online and offline. You can directly input and edit the ladder program, which is more intuitive and convenient, but the price is higher and the operation is more complicated. Most smart programmers come with a disk drive that provides a recorder interface and a printer interface.
The special programmer can only program several types of PLCs from specified manufacturers. The range of use is limited and the price is high. At the same time, because PLC products are constantly updated, the life cycle of dedicated programmers is also very limited. Therefore, the current trend is to use personal computer-based programming devices. Users only need to purchase programming software and corresponding hardware interface devices provided by PLC manufacturers. In this way, users can obtain high-performance PLC program development systems with less investment.
The personal computer-based program development system is powerful. It can not only compile and modify the PLC ladder program, but also monitor the system operation, print files, and system simulation. With the corresponding software can also achieve many functions such as data acquisition and analysis.
The PLC is equipped with a switching power supply for internal circuit use. Compared with ordinary power supply, PLC power supply has good stability and strong anti-interference ability. The stability of the power supply provided by the power grid is not high. Generally, the power supply voltage is allowed to fluctuate within the range of ± 15% of its rated value. Many PLCs also provide a DC 24V regulated power supply for powering external sensors.
8. Other external equipment
In addition to the components and equipment described above, PLCs also have many external devices, such as EPROM writers, external memories, human / machine interface devices, and so on.
EPROM writer is a kind of PLC external equipment used to solidify user program into EPROM memory. In order to make debugging the user program not easy to lose, often use the EPROM writer to save the PLC's internal RAM to the EPROM.
The semiconductor memory inside the PLC is called internal memory. Sometimes external tapes, magnetic disks, and storage boxes made of semiconductor memories are used to store PLC user programs. These storage devices are called external memories. The external memory is generally an interface provided by a programmer or other intelligent module to realize the transfer of user programs to and from the internal memory.
The human / machine interface device is used to realize the dialogue between the operator and the PLC control system. * Simple and * universal human / machine interface device consists of buttons, changeover switches, dial switches, indicator lights, LED displays, sound and light alarms, etc. installed on the console. For PLC systems, semi-intelligent CRT human / machine interface devices and intelligent terminal human / machine interface devices can also be used. The semi-intelligent CRT human / machine interface device can be installed on the console for a long time, and the information from the PLC is received through the communication interface and displayed on the CRT. The intelligent terminal human / machine interface device has its own microprocessor and memory. It can quickly exchange information with the operator, and connect with the PLC through the communication interface. It can also be connected to the PLC network as an independent node.
Hunan Hillray Electric Technology Co., Ltd. Record number: Hunan ICP No. 16017533-1
Phone: 0731-85578889-805 Fax: 0731-85578889-802
Contact: Manager Tang Mobile: 18182102868
Address: Building 2, Block B1E1, Phoenix Tianjie Garden, Beichen Delta, Kaifu District, Changsha 35040
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