Abstract: Based on the requirements of remote control of high-frequency transmitters and simplified design, a high-frequency transmitter control system based on PLC and touch screen was designed. It was networked with the existing system by combining ProfiBus bus and Ethernet technology. STEP7, WinCC, and Protool were used to complete the PLC programming, host computer HMI, and touch screen HMI design, respectively. The hardware configuration, network structure, frequency fine-tuning, HMI, and software design of the system are described in detail. This system design simplifies the network structure and improves reliability and stability. Keywords: High-frequency transmitter; Remote control; Focusing beam; Fieldbus; Programmable controller. 1. Introduction The focusing beam NB2 is a high-frequency system in the heavy ion accelerator system used to improve beam quality. Its working principle is shown in Figure 1. [align=center] Figure 1: Working principle diagram[/align] Charged particles with different velocities will be subjected to velocity modulation when passing through a vacuum accelerating cavity coupled with a high-power high-frequency signal, eventually causing the particle velocities to converge. If particle 1 moves in the beamline with a velocity of V1 and particle 2 moves with a velocity of V2, where V1 is less than V2, after the same amount of time, particle 2 reaches the negative half-cycle of the high-frequency signal, and particle 1 reaches the positive half-cycle of the high-frequency signal. Both are subjected to acceleration 'a' generated by the electric field force. As shown in Equation 1-1, after the same amount of time, the particle velocities tend to be consistent, thus improving the beam quality. V2-at=V V1+at=V Equation 1-1 The high-frequency transmitter system, as shown in Figure 2, mainly consists of four parts: high-frequency amplification, tank circuit, cooling system, and power supply system. The high-frequency amplification section is a two-stage amplification system composed of a solid-state broadband amplifier and vacuum tubes; the power supply system is mainly responsible for supplying power to the filament, grid, screen grid, anode, and broadband amplifier of the vacuum tubes; in addition, the entire transmitter is a system dominated by distributed parameters, therefore the tank circuit is an important component for improving the transmitter parameters and performance. Considering that the transmitter operates in an electromagnetic environment with a mixture of high voltage, low voltage, AC, DC, pulse and analog signals, in order to ensure the stability and reliability of the control system, Siemens S7-300 series PLC and touch screen were adopted, and the NB2 transmitter control system was designed in combination with Ethernet (industrial Ethernet) technology to realize the remote control of the transmitter. Ethernet network is an industrial Ethernet technology that uses commercial Ethernet communication chips and physical media to realize point-to-point connection between devices using Ethernet switches. It is a commercial product that can support 10M and 100M Ethernet at the same time. Its data packet can be up to 1500 bytes, and the data transmission can reach 10Mbps or 100Mbps; thus realizing high-speed data transmission [1]. [align=center] Figure 2: Transmitter block diagram[/align] 2. Composition of control system The control system is to realize the interlock protection of the transmitter, that is, if any parameter of the transmitter's cooling, power supply, electron tube, or tank circuit is abnormal, the system can realize alarm and take relevant emergency measures to ensure the safety of the system. The field control HMI (Human Machine Interface) is configured using a Siemens TP270, enabling local operations such as alarms, recording, printing, and parameter reading. It also allows remote operation of the cooling system, power supply, electron tube biasing, and excitation from the control room; and displays the system's operating status, acceleration voltage (D voltage), and other relevant parameters on the industrial PC's HMI in the control room. 2.1 Hardware Configuration of the Control System To achieve the above requirements, the system adopts the structure shown in Figure 3. In the field, a Siemens S7-300 PLC and a touchscreen TP270 serve as the local controller and HMI for the high-frequency transmitter. Then, it connects to the existing control network via Ethernet and a switch, and finally connects to the industrial PC in the control room via an Ethernet card to complete remote control. [align=center] Figure 3: System Structure and S7-300 PLC Configuration Diagram[/align] The configuration of the PLC used in the system is shown in Figure 3. The power supply module is a PS305, capable of providing DC24V voltage and DC5A current. The CPU is 313-2DP. This CPU module has 32 DI/DO points and two hardware pulses with a maximum frequency of 30KHZ to meet the pulse modulation and drive of the stepper motor in the slot. The SM338 module is used to read the absolute position encoding data of the motor transmitted through the SSI bus. In order to facilitate communication, the CP3413-1 communication processor module is configured, which can be directly connected to the SWITCH switch with twisted pair cable to access the existing control network. In addition, in order to generate high-precision analog control signals, the 16-bit precision SM332 module is used. The sampling signals are all 4-20mA signals. The system is configured with SM331 analog module to complete the parameter measurement. 2.2 Control of the slot fine-tuning capacitor When the excitation is adjusted to change the output energy of the transmitter, that is, to change the D voltage, the fine-tuning capacitor needs to be changed at the same time to match the coupling network and reduce the reflection coefficient [2]. The control of the fine-tuning capacitor adopts the closed-loop control structure shown in Figure 4. When the PLC receives an action signal from the local TP270 touchscreen (local control mode) or from WinCC (remote control mode), it calls the corresponding function block FC to generate pulse and direction signals. These signals are amplified by the driver and used to drive the stepper motor, changing the distance between the capacitor banks, thereby changing the capacitance value and matching the coupling network. The position sensor used is a SICK ATM60 SSI absolute position encoder. The position encoding data of the capacitor banks is transmitted in SSI protocol format to the S7-300 SM338 module, and then uploaded via Ethernet to the industrial PC in the control room for display in the WinCC-configured HMI. Simultaneously, the position encoding data is transmitted to the local TP270 touchscreen via Profibus for display in the local HMI configured with Protool. [align=center] Figure 4: Simplified diagram of the fine-tuning capacitor drag control of the slot circuit[/align] 2.3 Conditioning circuit In order to ensure the monitoring of various system parameters of the transmitter, the optical isolation analog measurement conditioning circuit with TP521 as the core is adopted as shown in Figure 5 [3]. As long as the variable resistor in the figure is adjusted and the coefficient factor of the SM331 module is set appropriately, the parameter can be accurately measured; and displayed in the configured HMI to achieve the purpose of remote monitoring of transmitter parameters. [align=center] Figure 5: Parameter measurement conditioning circuit[/align] 3. Software design The software design of the system mainly includes PLC software design, upper-level HMI design of industrial PC and HMI design of the local control touch screen TP270. The PLC program design mainly realizes the on-site data measurement, status monitoring, control strategy judgment and Wincc data communication with the upper computer. In the Wincc configuration software environment, the transmitter operation flowchart, status monitoring diagram, parameter measurement display diagram and parameter trend curve diagram are designed respectively; and it has alarm recording, report generation and printing functions. The HMI design for the locally controlled touchscreen TP270 was configured in the Protool environment, and its functions are roughly the same as those of the WinCC-configured HMI. As shown in Figure 6, its human-machine interface (HMI) is divided into an operation flow area, a transmitter parameter measurement and monitoring area, a transmitter status monitoring area, and a function selection area. [align=center] Figure 6: Operation Interface[/align] In Step 7, the program loop organization block is OB1. By judging the status of the operation variables from the upper industrial control computer WinCC or the touchscreen TP270 and the status of the PLC input contacts, it cyclically calls the power on/off function block FC20, the pulse width modulation generation block SFB49 and the background data block DB20, the parameter measurement function block FC21, the excitation signal adjustment function block FC22, the system interlock protection block FC23, and the function block FC24 for communication with DB. The entire program structure is shown in Figure 7. After the PLC is powered on and initialized, it enters the OB1 main loop block and scans the function block FC24 to achieve communication with Wincc and TP270, obtains operation information and connects the PLC's input contacts and auxiliary nodes such as M1.0, calls the corresponding function block FC, and completes the corresponding control operation; at the same time, it uploads the relevant data and parameter status to Wincc through FC24 to achieve remote monitoring. If the system parameters are abnormal at any time, the PLC will call the interlock protection block FC23 to put the system into the protection standby state and display the fault on the Wincc and TP270 operation interface to inform the system operator [3]. [align=center] Figure 7: Software structure diagram[/align] 5. Conclusion The system uses Siemens S7-300 PLC as the local controller, which has the advantages of strong anti-interference ability and reliable operation. By combining Profibus fieldbus and using the TP270 touch screen as the human-machine interface for local control, the scheme of using buttons, digital tubes, analog meters and other similar devices as human-machine interfaces has been replaced; the wiring of the system has been reduced, the design of the interface circuit has been simplified, and the design is simple, reliable, and intuitive. The HMI is configured with Wincc, which makes the host computer operation interface user-friendly, the status display intuitive, reduces the difficulty of operation, improves the level of automation, and saves human resources. The innovation of the author: By combining Profibus bus technology and touch screen, the traditional design idea of ​​using buttons, digital tubes, analog meters and other similar devices as human-machine interfaces has been changed. Under the harsh EMC (electromagnetic compatibility) conditions, the control of the transmitter system has been reliably realized. References: [1] Yang Xianhui. Industrial Data Communication and Control Network. Beijing: Tsinghua University Press. 2003.: 150-152. [2] Wang Xianwu. Automatic Frequency Tuning System of High Frequency D Circuit of Accelerator Based on PLC . Microcomputer Information, 2003, 12-1: 30-32.　　[3] Wen Lianghua. Transmitter control system retrofit based on PLC and Ethernet. Electrical Engineering Technology, 2007, 3-10: 2-3.　　Design of a transmitter control system based on PLC and touch screen