Application of embedded soft PLC virtual machine in electrical test
PLC uses OMRON CQM1H-CPU11 PLC plus expansion module, its number of I/O points can reach 26, which can meet multi-channel test. It can judge the product or load by using the timer difference between the timer of the control action relay and the load feedback relay. State, and system shutdown protection, after the completion of the experiment, the product or load is used to evaluate its products in terms of mechanical and electrical characteristics. 3. Virtual running system of embedded platform Next page A plate flange is a flat, circular disk that is welded onto the end of a steel pipe and allows it to be bolted to another pipe. Typically used in fuel and water pipelines, the two flange plates will be bolted together with a gasket in between them. The flange plate will have bolt holes all around the perimeter and will be used to create junctions, tees and joints. Plate Flanges,Flange Dimensions,Forged Steel Plate Flanges,Plate Flat Flange Shandong Zhongnuo Heavy Industry Co.,Ltd. , https://www.znforged.com
In the testing of some electronic component products, many manufacturers used relay contact control systems. The system consists of discrete components. Due to the simple circuit, the component control accuracy is not high, and the anti-interference ability level is poor, so the operation is not stable enough and the malfunction is frequent, which makes the product testing and analysis inaccurate. With the high precision requirements of modern technology, in order to adapt to the market demand, the original relay electrical control system is modified by programmable controller, but most of the hardware modules and software structures of PLC manufacturers are dedicated and incompatible. The interaction mode and communication mechanism of each module of the system are also different, which makes the control system relatively independent and closed to each other. As technology advances and market competition intensifies, this proprietary architecture control system is increasingly exposed to its inherent flaws. Because the software PLC based on the PC platform does not need a special programmer, it can make full use of the hardware and software resources of the PC, directly adopt ladder diagram or language programming, and has the advantages of good human-machine interface, so it gradually replaces the hardware PLC and becomes research. hot spot.
1. Introduction to the principle of electrical test system
The life test system can use a timer to control the operating frequency of the electronic component product, and uses a timer to control the number of actions. The basic principle is shown in FIG. 1 . 
Figure 1 Basic principles of electrical testing
Among them, the interrupt protection, the action relay and the load feedback Relay are all controlled by the PLC internal high-precision timer. The principle is to control the high voltage with low voltage to achieve high and low voltage separation, which ensures the safety of the test system. For the protection of the break, Fuji Electric Co. Ltd. JapanSC-13AA type contactor, withstand voltage up to 600V, single contact rated current is 32A, action relay and load feedback relay (can also use photoelectric coupling or current transformer) are used OMRON MY series relay.
Actually, the DL750 scoper measurement found that these two kinds of precision are not very high, and the error often has 8-10ms.
In practice, product evaluation requires a lot of data, and many products need to be tested. This requires multiple independent circuits, wiring is difficult, and parasitic circuits are generated. Therefore, considering the compatibility and testing cost of PLC products, the current advanced embedded system is adopted. Soft PLC technology can greatly shorten the test cycle and reduce costs.
2, soft PLC technology
After more than ten years of development, the traditional PLC has been very mature, and has been widely used in industrial control with high speed, high stability and high performance. At the same time, with the development of modern computer technology and electronic technology, Engineering has gradually shown its shortcomings: traditional PLC manufacturers monopolize the market, their product households are not compatible, lack clear and consistent standards, it is difficult to build an open hardware architecture; the programming methods of various manufacturers' products are very different, and the technology is more proprietary. Strong, long training time for staff, resulting in a very slow price-performance growth of PLC.
In the mid-1990s, the rapid development of computer and microelectronics technology and the development of PLC's international standard IEC61131 produced soft PLC technology. All "soft PLC technology" uses PC as a hardware support platform to realize standard hardware PLC using software. The basic function, that is, the PLC control function is packaged in the software, running in the PC environment, PC-based control system, while providing the same functions of the PLC, but has the advantages of the PC.
Soft PLC technology generally consists of two parts: the development system and the operating system. The development system runs on the PC platform, while the runtime system runs on the embedded hardware platform. Generally speaking, the embedded hardware platform must run some embedded operating system, such as μC/OS-II, μClinux, etc.
The characteristics of modern development systems are generally integrated development environments, friendly interfaces, and easy to use. The soft PLC embedded system is based on the IEC61131 international standard, so it is necessary to support several languages. The system runs on the embedded hardware platform and is responsible for interpreting the execution of the target files generated by the development system after compilation and linking. The running system is generally composed of It runs the kernel, communication interface and system management. Its design and implementation accuracy is very high, and its execution efficiency will directly affect the response speed of the system in the field control.
The structural composition of the operating system is shown in Figure 2. The main tasks of the System Manager are to handle different tasks, coordinate program execution, and read and write variables from I/O images. The I/O interface can communicate with local I/O systems and remote I/O systems. The communication interface enables the operating system to communicate with the development system or other devices. The kernel interpreter is the core part of the runtime system and is responsible for interpreting the object code that executes the PLC application compiled by the development system. 
Figure 2 Structure of the operating system