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After decades of development in electrical valve positioners, although the products offered by different companies vary, their basic principles remain roughly the same. A schematic diagram is provided below to illustrate this. Its basic structural components are shown in Figure 1. Its working principle is based on the principle of force balance. The feedback rod inside the actuator provides feedback on the changes in the valve’s opening position. When the electromagnetic torque generated by the input signal is equal to the torque produced by the actuator’s feedback system, the force balance system of the actuator is in equilibrium, and the actuator is in a stable state; at this point, there is a proportional relationship between the input signal and the valve position. When the input signal changes or forces exerted by the medium fluid change, the equilibrium state of the force-balancing system is disrupted. The force generated by the magnetoelectric components and the force produced by the feedback loop due to changes in the valve stem position become unbalanced. As a result of the action of the nozzle and baffle, the output pressure of the actuator’s air supply changes; this change in pressure within the actuator’s air chamber drives the actuator to move, positioning the valve stem in a new location that corresponds to the new input signal, thereby achieving a new equilibrium state. Working principle of intelligent electrical valve positioners: Intelligent electrical valve positioners share essentially the same control mechanism as traditional positioners; both adjust the output pressure signal by comparing the input signal with the position feedback. However, the actuating elements of intelligent positioners are completely different from those of traditional positioners, which means that their working methods are also entirely distinct. First, a microprocessor is used as the core, and secondly, new types of devices are employed. The Siemens SIPARTPS2 series of intelligent electrical valve positioners are based on microprocessors; they use new piezoelectric valves to replace the nozzle and baffle pressure-regulation systems found in traditional positioners, thereby enabling precise control of the output pressure and ensuring accurate positioning of the valve. Currently, many companies manufacture intelligent electrical valve positioners. The SIPARTPS2 series of intelligent electrical valve positioners produced by Siemens is a very typical and representative example. Taking the SIPARTPS2 series as an example, the working principle of intelligent positioners will be explained here. A valve stem position sensor detects the actual opening degree of the valve; this signal is converted into a digital code through A/D conversion. This digital code is then compared with the digital code of the input (set) signal in the CPU, and the difference between the two values is calculated. If this difference exceeds the positioning accuracy, the CPU issues commands to activate the corresponding on/off piezoelectric valves. That is, when the set signal is greater than the valve position feedback, the pressure-increasing piezoelectric valve V-1 opens, causing the output air pressure P1 to increase. As a result, the pressure in the actuator’s air chamber rises, which leads to an increase in the valve’s opening degree, thereby reducing the difference between the two values ； If the set signal is lower than the valve position, the novelty of the SIPARTPS2 intelligent electrical valve positioner in regulating the output air pressure lies in the following: 1) The output pressure is regulated using PID pulse width modulation (PWM) technology, ensuring rapid and accurate control. Since the CPU controls the piezoelectric valve using a five-step switching program, it is possible to precisely and quickly regulate the increase or decrease in the pressure of the output air supply. Its control algorithm generally employs digital PID regulation; the CPU performs PID calculations based on the magnitude and direction of the deviation between the input signal and the valve position, and outputs a PWM pulse signal to control the opening and closing of the piezoelectric valve. Since the width of the pulse corresponds to the change in the air supply pressure at the actuator’s output, it is possible to rapidly and accurately adjust the air supply pressure output P1. When the deviation is large, the regulator outputs a continuous signal that rapidly and significantly changes the value of P1. When the deviation is small, the regulator outputs a pulse signal with a narrower pulse width, causing P1 to change in a discontinuous and minor manner. When the deviation is very small (entering the dead zone), no pulses are emitted, and the valve position remains stable. 2) The use of new piezoelectric valve devices ensures high control precision. Since the key component of the piezoelectric valve is a piezoelectric flexible switch valve, also known as a silicon microcontrol valve, its low mass results in very low switching inertia, enabling it to operate at high switching frequencies. Thus, acting as a high-frequency pulse valve, it controls the output gas path pressure P1 and drives the actuator, achieving high precision in valve positioning. 3) The valve position feedback element features high positioning accuracy and a long service life. The valve position feedback element is a conductive plastic potentiometer with a simple structure, high precision, and high reliability; it converts the linear or angular displacement of the actuator into a resistance signal, thereby enabling accurate detection of the valve position. It also facilitates the setting of the valve’s zero point, full scale, as well as its flow characteristic curve. Okay, that’s it for now. If everything goes well, I’ll continue to update it. Do you know what to do? Follow!