1. Review of relay-connection control
Students answer the structure and principle of relay (contactor), draw the main circuit diagram and control circuit diagram of three-phase asynchronous motor
Students summarize the shortcomings of relay-connection control. This leads to "the emergence of PLC"
2. The emergence of PLC
The bidding requirements of American General Motors Corporation (GM) in p>68 are:
(1) Soft connection replaces hard wiring; (2) Easy maintenance; (3) Reliability is higher than relay control cabinet (4) Volume is smaller than relay control cabinet (5) Cost is lower than relay control cabinet (6) Data communication function (7). , the original system changes less (1) the storage capacity of user programs can be extended to 4K
Core idea:
replace hard wiring with programs
Input/output levels can be directly connected with external devices
The structure is easy to expand
This is the prototype of PLC.
in 1969, DEC developed the world's first PLC(PDP-14) and successfully applied it to GM's automobile production line
The birth of PLC:
In 1969, the United States developed the world's first PDP-14
In 1971, Japan developed the first DCS-8
1973. The first PLC developed in China
II. Features, present situation and development of PLC
(I) Features
(I) Small size; (II) High reliability; (III) Good flexibility; (IV) No requirements for environmental conditions; (V) Low price ... All functions required by the tender
(II). More than 8% of the equipment can be developed by using PLC
(3)
Development history:
The first generation: 1969 ~1972, and the representative products are
PDP-14 of DEC Company of the United States, SCY-22 of Lishi Electric Company of Japan, and Beichen Electric Company of Japan. The representative products are
LOGISTROT of GE Company of America
SIMATIC S3 and S4 series of SIEMENS Company of Germany
SC series of Fuji Electric Company of Japan
Third generation: 1976~1983, The representative products are
M84, 484, 584, 684 and 884 from GOULD Company of the United States
SIMATIC S5 series from SIEMENS Company of Germany
MELPLAC-5 and 55
The fourth generation: from 1983 to now, The representative products are
a59 of GOULD Company of the United States
S7 series of Siemens Company of Germany
Development direction:
Product scale is polarized
Handling analog quantity
Pursuing high reliability
Communication interface and intelligent module
System operation station is equipped with high-resolution monitor
Pursuing. Classification of PLC
According to structure:
Integral
Combined
According to I/O points and memory capacity:
Ultra-small: less than 64 points, 256 Byet ~ 1kB
Small: 65~128 points, 1~3. 6 kb
medium type: 129~512 points, 3. 6 ~ 13KB
Large type: 513~896 points, more than 13kb
Super large type: more than 896 points, more than 13kb
Fourth, the relationship between networked PLC and DCS
DCS originated from analog quantity
PLC originated from switch quantity
They are mutually permeated, complement each other, and functionally. Make the digital world and analog world more fuzzy
The application area of DCS and PLC is determined by its performance/price ratio
1. PLC is a new industrial control device based on computer technology. In the draft PLC standard issued by the International Electrical Committee in 1987, PLC was defined as follows:
The full name of PLC is Programmable Logic Controller in English and Programmable Logic Controller in Chinese. The definition is: an electronic system with digital operation, which is specially designed for application in industrial environment. It uses a kind of programmable memory for storing programs, executing logic operations, sequence control, timing, counting and arithmetic operations and other user-oriented instructions, and controls various types of machinery or production processes through digital or analog input/output. PLC is a programmable logic circuit and a language closely integrated with hardware, which has very important applications in semiconductors. It can be said that where there are semiconductors, there are PLC
"PLC is a special kind. It uses a programmable memory to store instructions for performing logical operations, sequential operations, timing, counting and arithmetic operations, and can control various types of machinery or production processes through digital or analog input and output. PLC and its related peripheral devices should be designed according to the principle of easy integration with industrial control system and easy expansion of its functions. "
features of p>PLC
2.1 high reliability and strong anti-interference ability
high reliability is the key performance of electrical control equipment. Because PLC adopts modern large-scale integrated circuit technology and strict production technology, its internal circuit adopts advanced anti-interference technology, which has high reliability. For example, the average time between failures of F series PLC produced by Mitsubishi Company is as high as 3, hours. The average trouble-free working time of some PLCs using redundant CPU is longer. As for the external circuit of PLC, compared with the relay contactor system of the same scale, the electrical wiring and switch contacts have been reduced to hundreds or even thousands, and the faults have been greatly reduced. In addition, PLC has the function of hardware fault self-detection, which can send out alarm information in time when a fault occurs. In the application software, the user can also program the fault self-diagnosis program of peripheral devices, so that the circuits and equipment in the system except PLC can also obtain fault self-diagnosis protection. In this way, it is not surprising that the whole system has high reliability.
2.2 complete sets, perfect functions and strong applicability
today, PLC has formed a series of products of various sizes. It can be used in industrial control occasions of various scales. In addition to the logic processing function, most modern PLC has perfect data operation ability, which can be used in various digital control fields. In recent years, a large number of functional units of PLC have emerged, which makes PLC penetrate into various industrial controls such as position control, temperature control and CNC. Coupled with the enhancement of PLC communication ability and the development of man-machine interface technology, it is very easy to use PLC to form various control systems.
2.3 is easy to learn and easy to use, and is welcomed by engineers and technicians.
As a general industrial control computer, PLC is an industrial control equipment for industrial and mining enterprises. Its interface is easy, and the programming language is easy to be accepted by engineers and technicians. The graphic symbols and expressions of ladder diagram language are quite close to the relay circuit diagram, and the functions of relay circuit can be conveniently realized only by a small number of switch logic control instructions of PLC. It opens the door for people who are not familiar with electronic circuits, computer principles and assembly languages to use computers to engage in industrial control.
2.4 The design and construction of the system is small, and the maintenance is convenient. It is easy to transform
PLC uses storage logic instead of wiring logic, which greatly reduces the external wiring of the control equipment, greatly shortens the design and construction cycle of the control system, and makes the maintenance easier. More importantly, it is possible for the same equipment to change the production process through changing procedures. This is very suitable for multi-variety and small batch production occasions.
2.5 is small in size, light in weight and low in energy consumption
Take the ultra-small PLC as an example. The newly produced variety has a bottom size of less than 1mm, a weight of less than 15g and a power consumption of only a few watts. Because of its small size, it is easy to be installed in machinery, and it is an ideal control device to realize electromechanical integration.
3。 The basic knowledge of PLC < P > 1.1 The development of PLC in the industrial production process, a large number of switches are controlled in sequence, which acts in sequence according to logical conditions, controls the interlocking protection actions according to logical relations, and collects a large number of discrete data. Traditionally, these functions are realized by pneumatic or electrical control systems.
4. Application fields of PLC
At present, PLC has been widely used in steel, petroleum, chemical industry, electric power, building materials, machinery manufacturing, automobile, textile, transportation, environmental protection, culture and entertainment and other industries at home and abroad, and the usage can be roughly summarized as follows.
4.1 Logic control of switching value
This is the most basic and extensive application field of PLC. It replaces the traditional relay circuit to realize logic control and sequence control, which can be used for single equipment control, multi-machine group control and auto production line. Such as injection molding machines, printing machines, stapler machines, modular machine tools, grinders, packaging production lines, electroplating production lines, etc.
4.2 analog control
in the process of industrial production, there are many continuously changing quantities, such as temperature, pressure, flow, liquid level and speed, which are all analog quantities. In order to make the programmable controller deal with Analog quantity, it is necessary to realize A/D conversion and D/A conversion between analog quantity and Digital quantity. PLC manufacturers all produce matching A/D and D/A conversion modules, so that programmable controllers can be used for analog control.
4.3 motion control
PLC can be used to control circular motion or linear motion. From the configuration of control mechanism, I/O module was used directly to connect position sensor and actuator in the early days, but now special motion control module is generally used. Such as a single-axis or multi-axis position control module that can drive a stepping motor or a servo motor. Almost all the products of major PLC manufacturers in the world have motion control functions, which are widely used in various machinery, machine tools, robots, elevators and other occasions.
4.4 process control
process control refers to the closed-loop control of temperature, pressure, flow and other analog quantities. As an industrial control computer, PLC can program various control algorithms to complete closed-loop control. PID regulation is a widely used regulation method in general closed-loop control system. Large and medium-sized PLC has PID module, and many small PLCs also have this function module at present. Generally, PID processing is to run a special PID subroutine. Process control is widely used in metallurgy, chemical industry, heat treatment, boiler control and other occasions.
4.5 data processing
Modern PLC has the functions of mathematical operation (including matrix operation, function operation and logic operation), data transmission, data conversion, sorting, table lookup, bit operation and so on, and can complete data collection, analysis and processing. These data can be compared with the reference values stored in the memory to complete certain control operations, and can also be transmitted to other intelligent devices by using communication functions, or printed and tabulated. Data processing is generally used in large-scale control systems, such as unmanned flexible manufacturing systems; It can also be used in process control systems, such as some large-scale control systems in papermaking, metallurgy and food industries.
4.6 communication and networking
PLC communication includes communication between PLCs and communication between PLCs and other intelligent devices. With the development of computer control, the factory automation network has developed rapidly, and all PLC manufacturers attach great importance to the communication function of PLC and have launched their own network systems. The newly produced PLCs all have communication interfaces, and communication is very convenient.
5. The domestic and international situation p>5. PLC
In the process of industrial production, a large number of switches are controlled in sequence, which acts in sequence according to logical conditions, controls the interlocking protection actions according to logical relations, and collects a large number of discrete data. Traditionally, these functions are realized by pneumatic or electrical control systems. In 1968, GM (General Motors) Company of the United States put forward the requirement of replacing the electrical control device. In the second year, Digital Equipment Company of the United States (DEC) developed a control device based on integrated circuits and electronic technology, which was applied to electrical control by programmed means for the first time. This is the first generation of Programmable controller, which is recognized as the first PLC in the world. < P > Limited by the conditions of components and the development level of computers at that time, the early PLC was mainly composed of discrete devices. Microprocessors appeared in the early 197s. People soon introduced it into programmable controller, which made PLC increase the functions of calculation, data transmission and processing, and completed the industrial control device with real computer characteristics. In order to facilitate the use of engineers familiar with relay and contactor systems, the programmable controller adopts ladder diagram similar to relay circuit diagram as the main programming language, and all computer storage elements involved in operation and processing are named after relays. At this time, PLC is the product of the combination of microcomputer technology and relay conventional control concept. After the development of personal computer (PC for short), for convenience and to reflect the functional characteristics of programmable controller, programmable logic controller (PLC) was named.
in the middle and late 197s, the programmable controller entered the stage of practical development, and computer technology was fully introduced into the programmable controller, which made its function leap. Higher operation speed, ultra-small size, more reliable industrial anti-interference design, analog operation, PID function and high cost performance have laid its position in modern industry. In the early 198s, programmable controllers have been widely used in advanced industrial countries. The development of programmable controller in this period is characterized by large scale, high speed, high performance and product serialization. Another feature of this stage is that the number of countries producing programmable controllers in the world is increasing, and the output is increasing. This indicates that the programmable controller has entered a mature stage.
from the 198s to the mid-199s, the development of PLC was the fastest, with an annual growth rate of 3-4%. During this period, PLC's analog processing ability, digital computing ability, man-machine interface ability and network ability have been greatly improved, and PLC has gradually entered the field of process control, replacing DCS system, which is dominant in the field of process control, in some applications.
at the end of the 2th century, the development feature of programmable controller is more suitable for the needs of modern industry. In terms of control scale, mainframes and subminiature computers were developed during this period; In terms of control ability, various special functional units have been born, which are used for pressure, temperature, rotation speed, displacement and so on.