Abstract: This paper details the working principle, hardware structure, and software design of actuators based on the EPA standard. Utilizing the multi-information transmission capabilities of the EPA standard, it realizes remote configuration, remote calibration, and remote fault diagnosis functions for the actuators, achieving the goals of intelligent, digital, and networked actuator equipment. Keywords: Actuator, Valve Positioner, EPA Standard, Ethernet Function Block 1 Introduction Actuators are an important component of process control systems, and can be classified into three main categories according to their driving energy form: electric, pneumatic, and hydraulic. Each has its own characteristics and is suitable for different applications. An actuator typically consists of an actuator mechanism and a control valve. The actuator mechanism is a device that generates thrust or displacement based on control signals. The actuator mechanism drives the control valve, changing the energy or material delivery rate, thereby enabling the production process to execute normally according to predetermined requirements. With the development of automation, electronics, and computer technology, more and more actuators have evolved towards intelligence, and many actuators already possess fieldbus communication and intelligent control functions. The EPA standard is an international fieldbus standard based on industrial Ethernet with completely independent intellectual property rights in China. This paper combines the structural and technical characteristics of traditional actuators to develop intelligent electric actuators and electric valve positioners that conform to the EPA standard, enabling them to have fieldbus communication functions. These actuators pass tests on EPA conformance and interoperability testing platforms. Simultaneously, utilizing the multi-information transmission capabilities of the EPA standard, remote configuration, remote calibration, and remote fault diagnosis functions of the aforementioned actuators are achieved, realizing the goals of intelligent, digital, and networked field devices. 2. Working Principle and Hardware Design of the Actuator Currently, mainstream actuator products have widely adopted microcontroller technology, partially achieving intelligent functionality and largely replacing traditional analog actuator products. However, they still primarily rely on the "old-fashioned but reliable" 4-20mA analog communication technology. With the development and popularization of fieldbus technology, people's familiarity with and confidence in fieldbus technology are constantly increasing. More and more control systems are trending towards adopting a fieldbus-based architecture, and digital protocols will become the preferred communication technology for 21st-century control systems. Therefore, this paper mainly describes the implementation of fieldbus communication technology based on the EPA standard in actuators. The actuators involved include two main categories: electric actuators and electric valve positioners. 2.1 The overall structure of the electric actuator is shown in Figure 1. The control circuit of the electric actuator mainly consists of a central control unit, an EPA communication module, a position detection unit, a torque detection unit, an infrared remote control and display unit, a fault detection unit, a local control unit, a motor control module, and a power supply circuit. The EPA communication card receives valve position control parameters from the controller and compares them with the current valve position of the electric actuator. Through a specific execution control algorithm, it drives the motor and reducer, thereby making the valve move to the corresponding position. The position detection technology adopts advanced contactless position feedback technology, which greatly improves positioning accuracy and service life. The torque detection unit uses a professional pressure sensor to dynamically measure the torque of the output shaft. The introduction of fault detection and EPA communication technology makes remote fault diagnosis of electric actuators possible. [align=center]Figure 1 Schematic diagram of electric actuator circuit[/align] 2.2 The overall structure of the electric valve positioner is shown in Figure 2. The control circuit of the electric valve positioner mainly consists of a central control unit, an EPA communication module, a position detection unit, a display and keyboard unit, a fault detection unit, a piezoelectric valve control circuit, and a power supply circuit. The EPA communication card receives valve position control parameters from the controller, compares them with the current valve position of the electric valve positioner, and drives the piezoelectric valve control circuit through a specific adaptive control algorithm. By controlling the intake or exhaust volume, the valve moves to the corresponding position. [align=center]Figure 2 Schematic diagram of electric valve positioner circuit[/align] 2.3 The design of the EPA communication card is shown in Figure 3. The EPA communication card mainly consists of a processor unit, RAM, program memory, watchdog circuit, Ethernet controller, Ethernet interface circuit, Ethernet power supply circuit, and interface circuit with the instrument card. The processor unit uses a low-power, high-performance 32-bit RISC ARM processor from ATMEL, which has the advantages of small size and adaptability to industrial environments. Its stability and reliability are completely trustworthy, and its computing speed can fully meet the requirements of communication and control. The Ethernet controller uses the ASIX AX88796, an NE2000-compatible Fast Ethernet controller. It integrates a 10/100 Mbps adaptive physical layer transceiver and 8K×16-bit SRAM, supporting various CPU bus types including the MCS-51 series, 80186 series, and MC68K series. The AX88796 performs 10Mb/s and 100Mb/s Ethernet control functions based on the IEEE 802.3/IEEE 802.3u LAN standard. The AX88796's address and data buses are connected to the CPU's address and data buses, respectively. The CPU controls the AX88796's operating status by reading and writing to the NE2000 registers via I/O, and exchanges data with the AX88796's internal SRAM cache through remote DMA FIFOs. Local DMA is used between the SRAM and the MAC core to send data to the MAC layer, and then via the internal PHY layer to the RJ45 interface. [align=center]Figure 3 EPA Communication Card Circuit Diagram[/align] 2.4 Ethernet Bus Power Supply Solution In harsh industrial environments, to reduce the complexity of on-site installation and improve safety and economy, it is generally desirable for the cables connected to field devices to not only transmit data signals but also provide power to the field devices, i.e., bus power supply. Bus power supply technology plays an important role in industrial field applications. There are two methods for powering field devices based on the EPA standard: bus power supply and network power supply. Regardless of the method, it is essential to ensure that the Ethernet communication signal and the power signal do not interfere with each other to guarantee the reliability of Ethernet communication, measurement, and control operations of the field devices. Ethernet-based Bus Power Supply This method uses modulation and demodulation. At the Ethernet signal output of the Ethernet hub or switch, the 24-48V DC power signal is modulated together with the Ethernet communication signal. At the Ethernet signal input of the field device, the DC power supply and the Ethernet communication signal are separated, and the 24-48V DC power is converted into DC operating power for the field device through DC-DC conversion, thus realizing Ethernet-based bus power supply. The drawback of this method is that it alters the electromagnetic characteristics of the network transformer and, to some extent, changes the transmission logic of Ethernet. Ethernet-based network power supply utilizes two spare twisted pairs from the four twisted pairs in the Ethernet transmission cable to directly provide 24-48V DC power to the field devices. This power is then converted to the operating power of the field devices by a DC-DC converter. This method overcomes the shortcomings of bus power supply. The electric valve positioner designed in this paper adopts network power supply. Furthermore, in the EPA-based Ethernet power supply solution, the safety and reliability of bus power supply are also carefully considered. 3. Software Design The software design of the actuator product based on the EPA standard adopts a modular design approach. Software development can be divided into three parts: EPA user application, EPA communication stack software package, and hardware driver module. The EPA user application includes the following three modules: EPA function block shell and AO function block, EPA electric or pneumatic actuator technology block, and the interface module between the EPA communication card and the actuator control circuit. The EPA communication stack software package includes the following modules: EPA deterministic scheduling and precise time synchronization algorithm, TCP/UDP/IP protocol software, EPA application layer services, EPA application layer service interface, and EPA management services, etc. The software hierarchy is shown in Figure 4. [align=center] Figure 4 Schematic diagram of software hierarchy[/align] 3.1 Hardware Driver The hardware driver module includes processor initialization (including startup code, peripheral device configuration, interrupt vector settings, stack settings, etc.), Ethernet controller driver (network interface initialization, receive and transmit initialization), FLASH driver, etc. 3.2 EPA Communication Stack Software The EPA communication stack software implements three tasks: namely, the implementation of data (including real-time and non-real-time data) transmission services and the service interfaces provided to the user layer, and EPA management services (including automatic device identification, system clock synchronization, system operating status management, device tag number and other information management, etc.). The EPA communication protocol is based on the TCP/UDP/IP protocol, providing real-time and non-real-time data transmission services between user layer applications. The EPA communication protocol implements three communication mechanisms: client/server, publisher/subscriber, and report distribution. The client/server mechanism is primarily used for uploading/downloading configuration information, querying device information, and downloading user-defined programs. Publisher/subscriber communication is used for the periodic transmission of real-time process information (such as measurement and control data), typically employing broadcast, multicast, and unicast transmission methods. Report distribution is used for transmitting alarm information in the control process, typically using multicast and broadcast communication. The EPA application layer service interface is developed based on the requirements of process control information transmission, providing data communication between user-layer applications and implementing the following services: domain management service, domain upload service, domain download service, event management service, event reporting service, confirmed event reporting service, change event monitoring condition service, variable access service, variable read service, variable write service, and information distribution service. EPA management services are a crucial component of the EPA communication protocol. EPA system management primarily performs the following system management functions: device identification, object location, address allocation, clock synchronization, and function block scheduling. The precise time synchronization algorithm implements the complete IEEE 1588 precise clock synchronization protocol, ensuring that the clocks of all devices on the EPA network are synchronized. The EPA deterministic scheduling engine implements the EPA deterministic scheduling mechanism, ensuring that only one device is sending messages on the network at any given time, fundamentally avoiding Ethernet message collisions. 3.3 EPA User Application The EPA user application mainly includes: EPA function block shells and AO function blocks, EPA electric or pneumatic actuator technology blocks, and interface modules between the EPA communication card and the actuator control circuit. EPA function blocks are defined based on IEC 61499. A function block encapsulates a specific function in the control process and provides an interface for the user. The user does not need to worry about the specific details of how the function is completed, but only needs to configure the corresponding control system according to the interface of the function block. The interface definition of the function block is divided into data input/output interfaces and event input/output interfaces. The event input interface is used to trigger the execution of a certain function algorithm in the function block, while the event output interface is used to notify other function blocks after the calculation of this function block is completed. The data input/output interface is used to transmit data used for function calculation. Each actuator contains an AO function block that conforms to the EPA function block standard. The AO (Automatic Actuation) function block converts input data (typically valve position control values ​​provided by the controller) into values ​​required by the hardware channels. Since the AO function block is designed as a hardware-independent standard function block, a mapping relationship is needed between the physical hardware channels and the AO function block. The technical block isolates the hardware channel data from the standard function block, and the AO function block provides hardware data information through channel parameters. Additionally, the technical block provides calibration and diagnostic functions for the actuator. The EPA (Electrical Automation System) function block standard specifies corresponding technical block specifications for electric and pneumatic actuators. Due to space limitations, these will not be detailed here. The interface module between the EPA communication card and the actuator control circuit primarily handles data exchange between the two. The specific implementation of the interface module depends on the overall product structure. For a single-CPU solution, this interface is a program module that handles data exchange between different program modules; for a dual-CPU solution, this interface is a communication interface, which can be serial or parallel communication, handling data exchange between the two CPUs. 4. Implementation of Remote Configuration, Calibration, and Fault Diagnosis Functions The EPA remote configuration, calibration, and fault diagnosis software enables remote configuration, calibration, and fault diagnosis of EPA actuators via network. These functions rely not only on EPA function block and technical block standards but also on XDDL-based EPA device description technology. The EPA device description file describes all resources in the EPA device, including function blocks, technical blocks, and physical blocks; however, due to space limitations, this will not be elaborated upon here. Based on the device description file, the EPA device management software provides online EPA device management functions, including online EPA monitoring, remote configuration, remote calibration, and remote fault diagnosis. The interface of the EPA actuator remote configuration, calibration, and fault diagnosis software is shown in Figure 5. [align=center] Figure 5 Schematic diagram of the remote configuration, calibration and diagnostic software interface for EPA actuators[/align] 5 Conclusion The EPA standard is an international fieldbus standard based on industrial Ethernet with completely independent intellectual property rights in China. The intelligent electric actuator and electric valve positioner designed in this paper conform to the EPA standard and have Ethernet communication function. They have passed the tests of the EPA conformance and EPA interoperability test platforms. At the same time, by utilizing the multi-information transmission capability of the EPA standard, the actuator can realize remote configuration, remote calibration and remote fault diagnosis functions, so as to achieve the purpose of intelligentization, digitalization and networking of field equipment.