Abstract: This paper starts from the mechanism of electric actuators and the problems existing in their field applications, and focuses on the design points of the position adjustment module for the technical transformation of traditional electric actuators. Keywords : Electric actuator; Intelligence; Position adjustment module; Closed-loop control 0 Introduction Traditional electric actuators are characterized by their simplicity and cost-effectiveness, and have been widely used in production process control systems in fields such as power, metallurgy, petroleum, and light industry. Electric actuators and servo amplifiers in China were designed uniformly in the 1960s, and there has been no major technological innovation for over 30 years. These electric actuators have poor control capabilities, require extensive maintenance, and involve numerous connecting cables, making it difficult to meet the needs of China's industrial automation level. Currently, the servo amplifier section配套 (matched) with most electric actuators typically consists of an input isolation amplifier circuit, a comparator, a trigger circuit, and a power output circuit. The input is generally isolated by a coil and then amplified by a magnetic amplifier; the comparator circuit generally uses a voltage comparator composed of discrete components; the trigger circuit uses a relaxation oscillation trigger circuit, which has poor stability and reliability; the power output circuit uses a thyristor output circuit, and the servo motor speed is fixed, resulting in poor output positioning effect. This type of electric actuator cannot obtain some of its own characteristic parameters during the control process, resulting in low control accuracy and reliability. It can only accept one type of input signal, such as current or resistance. The detected signal is then compared with the input signal, and the resulting control signal is sent to the drive circuit to control the actuator's displacement output. Although some electric actuators have alarm circuits, they lack interlocking protection measures, making them unsafe even under alarm conditions. Therefore, this type of servo-amplified electric actuator is not suitable for applications requiring high precision, reliability, and stability. How to achieve high-precision and stable operation of field electric actuators through a distributed control system (DCS) is a problem that many industrial and mining enterprises need to consider in their technological upgrading projects. This paper takes Zhejiang University Control's JX-300XDCS as an example and introduces how to design a Position Adjusting Type Module (PAT module) for commonly used domestic electric actuators to achieve closed-loop control of the electric actuator, improve valve positioning accuracy and safety, and simplify operation. 1 Design Mechanism of PAT Module The PAT module is specially designed for electric actuators, replacing the traditional servo amplifier. It can be regarded as a new type of servo amplifier with higher control accuracy, more complete functions, more advanced, safe and reliable, and integrated with DCS. 1.1 Hardware Design of PAT Module Electric actuators generally provide 5 signal points: 1 analog signal, used to feed back the position signal of the electric actuator; 2 digital contact input signals, used to feed back the 2 limit alarm signals of the electric actuator; and 2 drive interfaces for forward and reverse coils, used to connect power devices, such as solid-state relays and thyristors. Servo amplifiers or PAT modules can drive solid-state relays or thyristors through digital output signals, thereby driving the electric actuator to rotate forward or reverse. Electric actuators are generally used in harsh environments. In industrial sites, for the convenience of engineering implementation, valve position feedback signal lines, power supply lines and digital output signal lines are concentrated in the same cable, and crosstalk between signal lines is serious. Therefore, the hardware of PAT module must be strictly designed in terms of isolation, anti-interference and electromagnetic compatibility [2]. The PAT module design employs opto-isolation and electromagnetic isolation technologies. Analog signal processing circuits are isolated separately, while the switching signal sections are uniformly isolated. The switching output section further isolates low-voltage and high-voltage signals via solid-state relays, effectively overcoming interference between different signals. Simultaneously, further signal conditioning and protection measures are implemented in the analog signal processing and switching signal circuits. This results in the PAT module possessing strong anti-interference capabilities and excellent electromagnetic compatibility, significantly improving stability and reliability. Electric actuators are generally highly sensitive, meaning valve positions change significantly within a short timeframe. Their feedback signals are rapidly changing analog signals. Therefore, when designing the analog signal processing circuit, the filter constant of the filtering circuit should be as small as possible. At the same time, it is important to select a fast A/D chip, such as a successive approximation type A/D chip, which can quickly sample and track valve position changes in a timely manner, thus ensuring good control performance. Hardware interlocking protection has the advantages of timeliness and reliability. Therefore, in the design of the PAT module, limit alarm signals are used in the output drive interlocking protection: the upper limit alarm input participates in the output increase hardware interlocking, and the lower limit alarm input participates in the output decrease interlocking protection. When the valve reaches its upper or lower limit, the PAT module's output can be directly cut off by hardware, eliminating the need for CPU processing and ensuring timely and reliable operation. Since the PAT module drives the field electric actuator via a relay, the quality of the relay directly affects normal control. Compared to commonly used electromagnetic relays, solid-state relays are contactless switching relays assembled from solid components. Their inputs are isolated using optocouplers, requiring only a small current to operate. Because there are no moving parts inside the output section, they offer reliable operation, fast switching speed, high operating frequency, long lifespan, and no electromagnetic interference. Therefore, solid-state relays are recommended for applications with high adjustment frequencies. 1.2 PAT Module Software Design (1) Threshold: En, which is related to the overall inertia of the module, relay, and electric actuator. It is the correction value of the change value of the valve position of the electric actuator after the control signal of the PAT module is cut off; (2) Valve position stabilization time, which is the time for the electric actuator to move due to inertia: Toff; (3) Minimum action step, which is the minimum pulse length that can make the electric actuator move: Ton; (4) Minimum action step length, which is the change in the valve position of the electric actuator when the pulse with the minimum action step length is output: Smin; (5) Dead zone, also known as the insensitive zone, which is the control accuracy that the electric actuator can achieve. 1.2.1 PAT Module Control Scheme Design In the process of controlling the electric actuator, there are generally three control schemes that can be adopted: the first scheme is to use continuous long pulse control, the second scheme is to use full-range step adjustment control, and the third scheme is a control method that combines long pulse control and short pulse step drive [3, 4]. The first scheme has the advantage of rapid adjustment and a simple control algorithm. It only requires judging the relationship between the difference between the valve position setpoint Sv and the valve position feedback value Pv and the dead zone (DeadZoon): when Pv - Sv < DeadZoon/2, an increasing pulse is output to drive the electric actuator to rotate forward; when Pv - Sv > DeadZoon/2, a decreasing pulse is output to drive the electric actuator to rotate in reverse. To eliminate oscillations using this control scheme, the only way is to reduce sensitivity and increase the dead zone (DeadZoon). However, this DeadZoon is no longer a true dead zone, as it includes an inertial component. Field control has certain sensitivity requirements, so the shortcomings of this scheme are obvious, and it is not recommended. The second scheme inserts a pause phase during motor rotation, causing the speed control system to slow down, thereby reducing system inertia. This control method can effectively eliminate oscillations and greatly improve control accuracy. However, if this stepper-driven control method is used for the entire adjustment process, the adjustment time will be greatly increased, which is absolutely unacceptable in many industrial applications. The third control scheme (Figure 2) combines the advantages of the first and second control schemes. When the absolute value of the difference between the actual valve position value Pv and the setpoint value Sv is greater than En, the module uses long pulse drive; when the difference is between the threshold En and half of the dead zone (DeadZoon), a short pulse step control method is used, that is, the module outputs a short pulse for the Ton time and waits for the Toff time until the absolute value of the difference between the valve position value and the setpoint is less than half of the dead zone, that is, when the control accuracy is reached, the output stops, and one control process is completed. The PAT module adopts the above control scheme, which makes full use of the system's inertia and the characteristics of the electric actuator, effectively overcoming the overshoot and oscillation phenomena that occur in the control process of the electric actuator, and improving the control accuracy. The settings of En, Ton, and Toff should be appropriate, with no more than 2 to 3 short pulses being optimal, so as to speed up the adjustment time. 1.2.2 PAT Module Adaptive Function Design The technical performance parameters mentioned in the manual of general electric actuators, apart from external characteristics such as dead zone, hysteresis, lag, and working voltage, do not describe internal characteristic parameters such as Ton, Toff, and Smin. The PAT module's self-learning function can obtain the characteristic parameters of these electric actuators, providing strong support for the reasonable setting of these parameters. The self-learning function is designed based on the principle of artificial neural networks and employs a backpropagation algorithm. This design stems from the fact that the characteristic parameters of electric actuators change under different loads and valve position ranges. The PAT module judges the control effect of the electric actuator and promptly corrects the characteristic parameters based on the control effect, thereby achieving optimal control. When the load is large, the corresponding dead zone and threshold are smaller than in the no-load situation, Ton is longer than in the no-load situation, while Toff is shorter. In this case, the PAT module can intelligently judge the rationality of the set parameters (see Figure 2; the intelligent handling of excessively long Ton pulses is similar and will not be described in detail) and adjust them in time to ensure optimal control. 1.2.3 Enhanced Function Design of the PAT Module In practical applications, unexpected and special situations often occur. For example, some valves do not have valve position limit switches, in which case the limit interlock protection function of the PAT module becomes ineffective. By judging whether the valve position changes accordingly when the module is outputting, it can determine whether the electric actuator has reached its limit or is in a stalled state, thus timely cutting off the output and preventing motor burnout. The valve positioner of the electric actuator is also a vulnerable component, and valve position feedback line breaks are not uncommon. These unexpected situations can cause the valve position acquired by the PAT module to fail to reflect the actual valve position value. In actual use, the valve position value of the electric actuator serves as the controlled variable of the inner loop, while the controlled gas flow or liquid flow rate serves as the controlled variable of the outer loop. At this time, the inner loop is in an open-loop state, and the PAT module automatically switches from closed-loop control to manual operation. Users can manually operate the electric actuator through the PAT module based on the controlled variable of the outer loop, thereby ensuring the normal operation of the entire loop. 2 Conclusion As an important intelligent module in the Zhejiang University Control JX-300XDCS, the PAT module's stability, reliability, functional completeness, and good control effect have been fully proven in practical applications, especially in the steel and power generation industries, where its performance has been recognized by users.