Abstract : This paper mainly discusses the system integration application principle of Yonghong PLC and Yonghong HMI in the sterilization and drying of the pharmaceutical industry, and demonstrates the system integration advantages of isomorphic platform electromechanical automation products.
Keywords : microwave, vacuum, human-machine interface PLC
I. Microwave Generation Principle:
The device that generates microwaves is a magnetron. A PLC controls an intermediate solid-state relay to drive a step-up transformer, with a voltage of approximately 6000V. A magnetron is an electrovacuum device used to generate microwave energy. Essentially, it is a diode placed in a constant magnetic field. Electrons inside the magnetron, under the control of mutually perpendicular constant magnetic and electric fields, interact with a high-frequency electromagnetic field, converting energy obtained from the constant electric field into microwave energy, thus achieving the purpose of generating microwave energy.
Magnetrons can be divided into two categories based on their operating states: pulse magnetrons and continuous wave magnetrons.
A magnetron consists of a core and a magnet (or electromagnet). The core structure comprises four parts: the anode, the cathode, the energy output device, and the magnetic circuit system. The inside of the tube is maintained in a high vacuum state. The structure and function of each part are described below.
1. Anode
The anode is one of the main components of a magnetron, and together with the cathode, it forms the space where electrons interact with the high-frequency electromagnetic field. Under the influence of a constant magnetic field and a constant electric field, electrons complete the energy conversion within this space. In addition to collecting electrons like the anode of a regular diode, the anode of a magnetron also plays a decisive role in the oscillation frequency of the high-frequency electromagnetic field.
The anode is made of a highly conductive metal material (such as oxygen-free copper) and has multiple resonant cavities. The number of resonant cavities must be even, and the higher the operating frequency of the tube, the more cavities it has.
The anode resonant cavity is often of the form of a slotted, fan-shaped, or slotted-fan shape. Each small resonant cavity on the anode is equivalent to a parallel 2C oscillation circuit. Taking the slotted-fan shape cavity as an example, the slotted part of the cavity can be considered to mainly constitute the capacitance of the oscillation circuit, while its fan-shaped part mainly constitutes the inductance of the oscillation circuit.
The anode of the magnetron is coupled together by many resonant cavities, forming a complex resonant system. The resonant frequency of this system is mainly determined by the resonant frequency of each small resonant cavity, and we can also estimate the operating frequency band of the magnetron based on the size of the small resonant cavities.
In addition to generating the required electromagnetic oscillations, the anode resonant system of a magnetron can also generate various electromagnetic oscillations with different characteristics. To ensure that the magnetron operates stably in the desired mode, a spacer strip is commonly used to isolate interference modes. The spacer strip connects the anode fins one at a time to increase the frequency spacing between the operating mode and adjacent interference modes.
In addition, since electrons still have a certain amount of energy after energy exchange, these electrons hit the anode, causing the anode temperature to rise. The more electrons the anode collects (i.e., the greater the current), or the greater the energy of the electrons (the lower the energy conversion rate), the higher the anode temperature. Therefore, the anode needs to have good heat dissipation capabilities. Generally, power transistors use forced air cooling, and the anode has heat sinks. High-power transistors are mostly water-cooled, with a cooling water jacket on the anode.
2. Cathode
The cathode and its leads: The cathode of a magnetron is both the electron emitter and a component of the interaction space. The performance of the cathode has a significant impact on the tube's operating characteristics and lifespan, and it is considered the heart of the entire tube. There are many types of cathodes, each with different properties. Directly heated cathodes are commonly used in continuous wave magnetrons. These are made of tungsten wire or pure tungsten wire wound into a spiral shape, and after being heated to a specified temperature by passing an electric current, they acquire the ability to emit electrons. This type of cathode has advantages such as short heating time and strong resistance to electron bombardment, and is widely used in continuous wave magnetrons. This type of cathode requires a large heating current, necessitating short and thick cathode leads and good contact at the connection points. The cathode leads of high-power tubes operate at very high temperatures and are often cooled by forced air cooling. When the magnetron is operating, the cathode is connected to a negative high voltage; therefore, the lead section should have good insulation properties and meet the requirements of vacuum sealing. To prevent overheating of the anode due to electron backfire, the cathode current should be reduced according to regulations after the magnetron has stabilized to extend its service life.
3. Energy output device
An energy output device is a device that delivers microwave energy generated in the interaction space to a load. The function of the energy output device is to transmit microwaves without loss or breakdown, maintain the vacuum seal of the tube, and facilitate connection to external systems. Low-power continuous-wave magnetrons mostly use coaxial outputs located at the point of strongest high-frequency magnetic field in the anode resonant cavity. A coupling loop is placed; when the magnetic flux through the loop changes, a high-frequency induced current is generated on the loop, thereby diverting the high-frequency power outside the loop. The larger the area of the coupling loop, the stronger the coupling. High-power continuous-wave magnetrons commonly use axial energy output devices, with the output antenna connected to the anode fins through pole shoe holes. The antenna is generally made in the shape of a strip, rod, or cone. The entire antenna is sealed by the output window. The output window is usually made of low-loss glass or ceramic. It must ensure lossless microwave energy transmission and have good vacuum tightness. High-power tubes often use forced air cooling for the output window to reduce heat generated due to dielectric losses.
4. Magnetron in the magnetic circuit system
A strong, constant magnetic field is required for normal operation, typically with a magnetic field strength of several thousand gauss. The higher the operating frequency, the stronger the applied magnetic field. The magnetic circuit system of a magnetron is the device that generates this constant magnetic field. Magnetic circuit systems are broadly classified into permanent magnet and electromagnetic systems. Permanent magnet systems are generally used in low-power tubes, where the magnet and the core are firmly integrated into a single unit, forming a so-called packaged system. High-power tubes often use electromagnets to generate the magnetic field. The core and electromagnet work together, with upper and lower pole shoes inside the core to fix the distance of the magnetic gap. When a magnetron is working, the output power and operating frequency can be easily adjusted by changing the magnitude of the magnetic field strength. Additionally, the anode current can be fed into the electromagnet coil to improve the stability of the tube's operation.
II. Precautions
Since the heating element of the equipment uses microwaves, interference from microwaves must be considered. Yonghong PLCs are independently developed products, with all controls integrated onto a single chip called "SOC" (System-on-Chip), resulting in strong anti-interference capabilities. Because the equipment requires heating control, analog modules are essential. The heating sensor in this equipment is a far-infrared sensor with a signal range of 4-20mA. Yonghong PLC's analog input board has a 12-bit precision and reads the analog value in each scan cycle, providing real-time updates. Combined with the reasonable price of the analog input board, it is acceptable to customers.
III. Process Flow
IV. Introduction to Yung-Hong Electric
Founded in Taiwan in 1992 by a group of engineers with many years of experience in PLC design, Yung-Hung Electric Co., Ltd. launched its FBE and FBN series products in 1993. After years of effort, the company launched its new FBS series in 2003, which received widespread acclaim in the industry. Yung-Hung has always focused on the high-performance small-to-medium-sized PLC market, and its own brand, "FATEK," enjoys a high reputation in the industry. Providing customers with high-performance, cost-effective products has always been Yung-Hung's mission, and years of dedicated work and practice have finally yielded fruitful results.
V. Human-Computer Interface
The human-machine interface uses Yung-Hong Electric's new product: a 5.7-inch touchscreen.
Figure 1 shows the parameter settings for a microwave vacuum drying and sterilizing machine.
Figure 2 shows the motion control of a microwave vacuum drying and sterilizing machine.
Figure 3 shows the manual control of each magnetron in the microwave vacuum drying and sterilizing machine.
Figure 4 shows the automatic status control of the microwave vacuum drying and sterilizing machine. Each temperature setting and time is displayed. After the first temperature setting ends, it automatically jumps to the second setting, and so on.
VI. Analog Panel Description
Temperature control is achieved using the cost-effective Yung-Hong FBS-B4AD analog input board. The FBS-B4AD is a 12-bit precision analog input board with a unipolar measurement range of 0-20mA or 0-10V. The Yung-Hong PLC design uses a 14-bit representation, i.e., 0-16380 corresponding to 0-20mA or 0-10V, with a maximum resolution of 2.44mV (voltage) and 4.88µA (current). The direct register reading method facilitates programming, occupying fixed addresses from D4072 to D4075.
VII. Conclusion
Yung-Hong's superior quality, powerful application command functions, and diverse communication methods have enabled us to play a crucial role in production and design. With the enrichment and development of Yung-Hong's electromechanical products, and the continuous improvement of their functions, coupled with customers' demands for comprehensive services, our products possess broad and promising market expansion potential.
