Application of Programmable Controller Laboratory in Crew Education

With the rapid development of microelectronics and computer technology, PLC (programmable controller) not only replaces hard-wired logic with logic programming, but also adds the functions of operation, data transmission and processing, and truly becomes a computer industrial control device. The functions of PLC far exceed the scope of logic control and sequential control, so in industrially developed countries, PLC accounts for the largest proportion of their automation equipment. In recent years, China's PLC technology has also moved from the initial introduction, digestion and promotion and application stage to the absorption and promotion and application stage, and has achieved good economic and social benefits in many industrial fields. Faced with this situation, it is very necessary for colleges and universities to popularize PLC technology education in relevant departments in order to better adapt to the development of China's economy, science and technology and society. For maritime colleges and universities, with the increasing degree of ship automation, PLC technology is gradually promoted and applied in main engines, auxiliary engines and power stations. This requires that maritime education must adapt to it, especially the marine engineering major must strengthen the education of PLC technology. At the same time, in order to meet the requirements of the IMO (International Maritime Organization) STCW 78/95 Convention, in addition to the PLC principle and application included in the "Marine Automation" course for undergraduate and junior college students of the school's marine engineering department, the marine electrical crew training course commissioned by the Maritime Safety Administration also requires the opening of the "PLC Principle and Application" course, supplemented by a certain amount of experiments. In view of this, the establishment of a PLC laboratory for crew education has become an urgent task.

2. Overall plan for establishing a PLC laboratory

The laboratory is the foundation of discipline construction and development, the base of teaching and scientific research, and an important indicator of the level of education and scientific research of colleges and universities. Therefore, the goal of our PLC laboratory construction is to build a high-standard open laboratory that can adapt to modern crew education and meet the requirements of the STCW 78/95 Convention. The laboratory consists of two parts:

1. Basic experiment part - Make a batch of standard experiment boards with PLC as the core, the input end is composed of several switches and sensors, and the output end is some indicator lights, relays and fuses. Because PLC experiments are different from general electrical and electronic experiments, they need to be programmed by themselves and input PLC debugging. They are hands-on, but the failure rate is high. With standard experiment boards, safety and intuitiveness are improved. Teachers can let students practice boldly, let them choose their own topics, connect their own circuits, and debug themselves. The role of the instructor in the whole process is only to guide, check, check and solve students' difficult problems.

2. Research and development section - Provide a place for teachers to conduct scientific research and technology development. Give full play to the technical advantages of professional teachers to solve some PLC application problems for shipping companies and related departments, conduct simulation tests or do some product development. This not only gives back to the society, but also provides conditions for the school to raise teaching and scientific research funds, and at the same time can improve the scientific research and teaching levels of teachers. The main equipment includes computers, special programming software, data connections and several sets of PLCs.

3. Construction of PLC Laboratory

At the end of 1999, our institute purchased 12 sets of FX2N-48MR micro programmable controllers and 1 set of FX-2P portable programmers from Mitsubishi. We designed and made ten experimental boards using these devices. The outer shell was formed by bending a metal sheet and then treated with electrostatic spraying (egg blue). In the middle was the PLC (for easy viewing of the status indicator LEDs of the input and output terminals on the PLC). In the upper left corner were the ~220V power input, switch, power indicator light, DC24V terminal and fuse. Considering the convenience of students' operation, we placed the input control switch and sensor terminal in the lower half of the experimental board, and the output relay, AC contactor, terminal and indicator light in the upper half (the PLC input terminals X0~X27 are on the top, and the output terminals Y0~Y27 are on the bottom). Since the output circuit of the PLC has no built-in fuse, in order to prevent the PLC base wiring from being burned out by load short circuit and other faults, a 5A fuse is set for every 4 output points (that is, a COM point). The PLC has excellent performance and has three types of outputs: relays, triacs and transistors. It can be connected to a variety of input and output expansion devices, and many experiments can be completed using simple instructions. In order to make the experimental teaching effect more ideal, several teaching boards were also made for demonstration. Since March 2000, we have opened three basic experiments in accordance with the newly compiled experimental instructions: "Understanding of the Basic Composition and Input and Output Interfaces of PLC", "PLC Programming of Light Cycle Lighting and Delay Lighting", and "Demonstration of PLC Application in AC Motor Control System". Considering the current widespread application of PLC on ships, such as main engine remote control, ship alarm monitoring, fuel boiler automatic control and other systems, and also to adapt to the new characteristics of crew education under modern conditions, we have gradually developed several ship equipment simulators for teaching with PLC as the core. The following is a brief introduction to the boiler control simulator as an example:

The boilers used in diesel engine power units are called auxiliary boilers. Since there are many such auxiliary equipment in the ship's engine room, the automatic control of the auxiliary equipment is one of the necessary conditions for realizing an "unmanned" engine room. To realize the automatic control of the auxiliary boiler, we must first understand its combustion sequence control, as shown in Figure 1.

According to the control block diagram of the boiler, we formulated the overall structure of the program. Considering that it is a simulator, we specially added a fault setting part to enhance the teaching function. We downloaded a Mitsubishi FX2N programming software from the Sinan Industrial Control website, bought a dedicated data cable, and started to write the boiler control simulator program. After the first draft of the program came out, it was repeatedly scrutinized and debugged paragraph by paragraph before it was fully input into the PLC for final testing. The corresponding hardware and wiring were also completed at the same time. The final program consists of 358 sentences and 719 lines. For example, Figure 2 provides a ladder diagram of the ignition process. The shape of the simulator is a floor cabinet. The shell is made of thin metal plates that are bent and welded and electrostatically sprayed (egg blue). The upper part is the indicator light, buzzer and instrument, and the middle inclined protruding part is the control panel (divided into three parts, see the following description).

Figure 3 System diagram of boiler control simulator

Figure 3 is a schematic diagram of the boiler control simulator. The panel is mainly composed of three parts: combustion control, water level control and fault setting. The layout is relatively simple and intuitive. Our institute has a boiler laboratory with a set of modified Japanese old boilers for teaching use. However, in terms of teaching and scientific research, real equipment also has obvious shortcomings, such as frequent start-up and easy damage, high operating costs and many faults cannot be reproduced, etc. The simulator makes up for these shortcomings.

IV. Conclusion

Since the establishment of the PLC laboratory, nearly 600 people have conducted experiments, and teachers and students generally responded well. It has also passed the acceptance of the Maritime Administration and other management agencies. This is of great significance for better adapting to the requirements of the IMO (International Maritime Organization) STCW 78/95 Convention and improving the quality of seafarer education and training management at Ningbo University. Of course, there are still deficiencies in the laboratory, which need further improvement and development. We plan to take the PLC laboratory to a higher level in three aspects: expanding experimental projects, continuing to develop ship engine room equipment simulators that apply PLC, and adding PLC brands and models to experimental equipment.