Dear readers, in the long river of science and technology, there is always a group of people who contribute their wisdom and strength to the prosperity and development of the industry with their profound professional knowledge and unremitting spirit of exploration. Today, we are honored to invite an old expert with rich experience and outstanding achievements in the field of electrical automation to become a resident author of Liancheng Technology.
Fang Yuanbai was born in Huanggang, Hubei in 1942. He is a professor-level senior engineer in the Electrical Automation Technology Department of Kunming Nonferrous Metallurgical Design and Research Institute. He is an editorial board member of magazines such as Automation Instruments, Weighing Instruments, Metallurgical Automation, Instrument World, Instruments and Automation, etc. He is the chairman of the Kunming Instrument Society and a consultant to the Technical Expert Committee of the China Weighing Instrument Association. He is mainly engaged in the application research of instrumentation and control systems. He has published six monographs, including "Principles and Applications of Electronic Belt Scales" (1994, Metallurgical Industry Press), "Electronic Belt Scales" (2007, Metallurgical Industry Press), "Wireless Communication Technology and Application in Process Industry" (2015, Chemical Industry Press), "Automation of Nonferrous Metal Production Process" (2015, People's Posts and Telecommunications Press), Checkweighers (2020, China Standards Press), and "Metal Detectors" (2023, Chemical Industry Press), and has published 380 papers.
Picture by Fang Yuanbai
In the coming time, Professor Fang will share with you his experience and insights in the field of industrial control through a series of articles. These articles not only embody the wisdom and insights accumulated from his decades of work, but also provide valuable reference and guidance for the majority of electrical automation practitioners and enthusiasts.
In this issue, we are pleased to introduce Professor Fang’s first work, “My Fate with PLC”.
The following is the original text:
01 PLC History Overview
It is said that in 1969, DEC of the United States developed the world's first PLC, which was applied to the production line of General Motors of the United States. Before that, various types of sequential control and time program control successively used relays, semiconductor logic elements, etc., which were not only large in size, poor in reliability, and required hard wiring, but also when the products of the production line changed, the programs and hard wiring of the above control devices had to be modified, which was equivalent to starting all over again. The advent of PLC changed all this. The program may be slightly modified (but it can be compiled in advance and downloaded when needed), but the hard wiring does not need to be changed, so it quickly became popularized.
Around the late 1970s, PLCs were introduced into China along with foreign-imported projects. At that time, several projects in the first phase of Shanghai Baosteel introduced more than a dozen models and about 200 sets of PLCs, which were used in the entire steel smelting and processing production line from the raw material terminal to the blast furnace, steel rolling, steel pipes, etc., replacing the traditional relay logic system.
Later, more than 600 sets of PLCs of more than 30 types from multiple foreign manufacturers were used in the second and third phases of Baosteel. Nearly 200 sets of PLCs from Rockwell Automation were also introduced into the diesel engine production line of Guangxi Yuchai Machinery Factory. In 1982, Tianjin Automation Instrument Factory was the first to introduce PLCs from Modicon of the United States. Later, foreign manufacturers also began to promote PLCs in China.
According to the information, China developed the first PLC in 1974, but in fact, it was just a programmable sequence controller using a 2-bit microprocessor chip and was not put into practical use. In 1977, after adopting the American MCI4500 integrated chip, the PLC developed was mass-produced and applied to industrial production. The earliest research and development manufacturers and scientific research units launched products such as LC-0088 from the Institute of Automation of the Chinese Academy of Sciences, GK40 from Beijing Lenovo Computer Group, CKY40 from Shanghai Machine Tool Electric Factory, and Yz-PC-0001DENG from Suzhou Computer Factory.
In recent years, the main PLC manufacturers in China include Zhejiang Zhongkong's GCS series G5 medium and large hybrid control system/G3 distributed control system, Wuxi Xinjie Electric's XC/XD/XL/XG/XS/CCSD, Nanda Aotuo's NA600/NA400/NA200, and Hubei Huangshi Kewei, Ankong Technology, Shanghai Zhenghang Electronic Technology, Shenzhen Huichuan Technology, Shenzhen Yingwei Technology, Beijing Hollysys and a large number of other companies. Yunnan also has professional PLC manufacturers such as Liancheng Technology Group.
02 First Look at PLC
In the late 1970s, PLCs for foreign engineering projects entered China. I was working in Kunming, where information was relatively isolated. But in 1982, the then Ministry of Metallurgy held a PLC training course in Beijing, and electrical engineers from our institute participated.
In early 1983, our institute invited experts from the Beijing Automation Research Institute of the Ministry of Machinery, which represented the programmable controller products of Texas Instruments (TI), to come to Kunming to introduce PLC. In 1984, in the engineering design of Kunming Coking Gas Plant designed by our institute, we selected the medium and large programmable controller PM550 and the small programmable controller 5TI of Texas Instruments.
Among them, PM550 not only has logic control function, the switch quantity can be connected to 256 input points and 256 output points at most, but also has PID loop control function, which can realize up to 16 PID loop control functions. Although it was still the mid-1980s, I was still able to accept the concept of control system integration. I was one of the first in China to cooperate with the automatic control major I was engaged in and select a set of PLC to realize the monitoring of the electrical and automatic control majors of the entire coking plant. The electrical major was responsible for the overall and switch quantity part of the PLC, and I was responsible for the analog loop and analog quantity part.
In 1986, the coking gasification plant entered the commissioning stage. Our institute was responsible for the on-site programming, commissioning and commissioning of the PM550 programmable controller. The programming device at that time was a VPU200 display programmer. The information that came with the programmer and controller was all in English. The English that I had learned by myself a few years ago also came in handy. I translated all the English information of the programmer. The program part involved two majors, electrical and automatic control. The automatic control part was also a program written by me. This program was filled in the form item by item, that is, filling in the loop programming work sheet, and then arranging a subroutine that called the work sheet in the program written in the ladder diagram (see Figure 1).
Figure 1 PID loop worksheet
At that time, I also used a Texas Instruments 5TI small programmable controller, which was relatively small, so I could learn programming in my dormitory, then program according to the process requirements and use the simulator for debugging. The debugging equipment in Figure 2 is the 5TI small programmable controller, programmer, and simulator.
Figure 2: I programmed and debugged the Texas Instruments 5TI PLC before installing it on site (I was still young at that time!)
After the project was completed, I published several papers:
Application of PM550 programmable controller in coal blending in coking plant (Fuel and Chemical Industry, 1988.03);
The loop control function and application of PM550 programmable controller (Nonferrous Metal Design, 1989.02);
Development of PC software for material accumulation calculation (Industrial Instrumentation and Automation Equipment, March 1990)
03 Product Development
Because I had the opportunity to get in-depth contact with PLC, I have some understanding of PLC's functions and programming, and I often think about what occasions these PLC functions will be used.
At that time, I was the person in charge of the engineering design and automatic control department of Kunming Coking Gas Plant. The instruments selected for the design were mainly Yokogawa I series panel-mounted instruments and Rosemount 1151 transmitters introduced by Xi'an Instrument Factory, and their use was good. However, there was one type of instrument that was used in almost every process, but had a very high failure rate. This was the flash signal alarm.
At that time, we used a domestic eight-circuit alarm using transistor circuits and integrated circuits. Generally, one or two circuits would fail after three to five months of use, and after one year, the alarm would be scrapped. I was very annoyed and kept thinking about what to do. When there is a problem in the engineering design, you must read the information, think about it and study it in depth.
So at that time, I sent letters to N manufacturers of flash signal alarms to request information, and received a total of more than 20 letters and information replies from manufacturers. Then I calmed down, checked and summarized the information one by one, and wrote an article: "The Current Situation and Development of Flash Signal Alarms" (Automation Instruments, 1991.01). It introduced the current situation, listed the various alarm functions of domestic flash signal alarms, the alarm functions and program flowcharts of the imported American Rochester alarms, and suggestions for the product development of flash signal alarms. Figures 3 and 4 are the functions of conventional alarms and high-end SA F3A program alarms, respectively. Looking at Figure 4, you will know that the SA F3A program alarm has complex functions and can identify the first alarm signal (i.e., the first-out signal) from multiple alarm signals that are almost alarmed at the same time.
Figure 3 General alarm function
Figure 4 SA F3A program alarm function
After doing this work, an idea came into my mind: the alarm program of the flash signal alarm is a logic judgment of the switch quantity. It judges whether the switch input signal meets the alarm condition. If it meets the condition, the switch outputs the light signal and the sound signal. Think about PLC again. It is best at the logic judgment of the switch quantity, so there should be no problem in writing the alarm program. The rest is economical. PLC is only used for alarm, which is a waste of resources. Is it economical? It is definitely not economical to use the imported or introduced PLCs seen on the market at that time.
At a technical exchange meeting held in Kunming, we saw a small PLC model YZ-PC-001A produced by Suzhou Computer Factory, the earliest PLC manufacturer in China at that time. We signed a contract to buy their products, and they also left a physical PLC brought to Kunming (with a CPU board and 48-point DI and 16-point DO) for us to try out. They also left a programmer and a signal simulator (with a row of button switches and a row of signal lights on it, the button switches simulated switch input signals, and the signal lights simulated switch output signals).
With a PLC and a simulator, I feel at home and can seriously learn this PLC. First, learn each of its functions according to the samples and programming manuals that come with it, and do the functional examples given in the manual, so that you can actually understand the various functions of this small PLC.
After a week of basic learning, I started to implement the alarm program of the flash signal alarm using PLC. The programming work was to compile the program according to 4 alarm input points first, and then if 8, 16, 24, 32, or 48 alarm points were needed, the 4-point program could be reused.
After I compiled all the 10 existing alarm programs I had summarized, I demonstrated them one by one on the simulator to prove that the programs were compiled correctly. This new flash signal alarm is not only reliable (it has the reliability of PLC, and the user can choose which alarm program to use, and can also change to another alarm program as needed in the future), but its price is much lower than that of imported products, and is comparable to the price of domestic 8-point flash signal alarms.
After the product was developed, it was transferred to Guiyang Yongqing Oscilloscope Factory and Kunming Jinding Power Supply Complete Equipment Factory. The product was rated as a provincial-level new product in Yunnan Province, and dozens of units were used in the second phase engineering design of Kunming Coking Gas Plant and other engineering projects.
Listed below are ladder diagram programs (see Figure 5) that replace the functions of conventional flash signal alarms (with signal memory and automatic reset functions) and ladder diagram programs (see Figure 6) that replace the functions of the most complex flash signal alarms (with signal memory, first-out display, first-out reset, and automatic reset functions).
Figure 5 Ladder diagram program for conventional alarm functions
Figure 6 Ladder diagram program for the SA F3A program alarm function
After the work was completed, I published several papers on flash signal alarms:
Microcomputer multifunctional flash signal alarm (Nonferrous Metal Design, 1991.04);
Development of signal flash alarm function (Industrial Instrumentation and Automation Equipment, 1992.06);
PC Programming of Complex Signal Flash Alarm Function (Journal of Kunming Institute of Technology, 1993.06);
04 Meet OPLC again
In 2003, Kunming Kandel Company bought a batch of OPLCs (Operator panel and Programmable Logic Controller, PLC with operator panel) from Unitronics of Israel. This is a small PLC that integrates the PLC's HMI human-machine interface with the PLC complete machine (including CPU and I/O cards) (see Figure 7).
Figure 7 Unitronics' M90/M91
This pocket-sized device that can fit in the palm of your hand integrates a micro PLC with 14 to 24 I/O points and an operation display panel with a keyboard, so it is called All-in-One. On the operation display panel, we can see an LCD liquid crystal display, which is a text display that can display up to 1 or 2 lines of 16 characters (with backlight). There are 15 sealed diaphragm keys under the operation display panel, and the keyboard can be used to communicate information with the M90/M91 and modify existing data.
The host itself can carry I/O points from 14 to 24 points; after adding I/O expansion modules, up to 8 I/O modules can be connected, and up to 64 I/O points can be expanded; up to 63 M90/M91 can be connected to a network through the bus. Some models can accept 1 to 2 analog input signals and 1 analog output signal, and can realize PID loop control. With RS232 serial port, support GSM function.
Ladder diagram programming and operation display panel programming are performed on the PC. OPLC is small, inexpensive and feature-rich. It is particularly suitable for use in PLCs that are used with small devices. What is particularly trendy is that it also has the function of wirelessly sending and receiving SMS messages containing fixed text and variable data. On the one hand, I feel that it is cheaper and more suitable for use as the host of a flash signal alarm. On the other hand, I am more interested in the function of wireless transmission of SMS messages.
In the process of studying OPLC, the following articles were published:
M90/91 micro OPLC (PLC&FA, 2004.02);
The development of micro programmable controller with HMI (World Instrumentation and Automation, 2004.08);
Mobile phone short message service and remote monitoring system (Automation Expo, 2004.04);
Siemens C7 series integrated PLC, (Industrial Automation, 2005.03);
PLC or Intelligent Relay (Control Engineering-China, 2007.04);
Application of ultra-micro integrated PLC (PLC&FA, 2010.12).
Since I had initial exposure to the wireless sending and receiving SMS short message function, when WirelessHART and ISA100.11a, wireless technologies for the process industry, came out in 2007, I quickly accepted this technology and started my new research topic: wireless technology for the process industry.
05 Conclusion
As a professional automatic control designer, although PLC is not my main business, I have been exposed to it and learned about it intermittently over the years, and I am also very concerned about it when reading materials. After thinking about it, I have been closely associated with PLC for forty years. With the rapid development of PLC technology, I have also continued to grow and made some progress.
This process can be summarized in one sentence: I, an old man, have a connection with PLC!
