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This article is reproduced from: http://www.azbil-positioner.com/a/Xwzx/197.html. Keywords of this article: valve positioner. Valve positioners are widely used in daily life and are very popular among the public. The internal structure of this locator is clear and simple; it mainly consists of a SPAN span adjustment mechanism, an amplifier, a feedback cam, a constant-throttle orifice, nozzles, a zero-point adjustment device, baffles, etc. Its internal working principle is basically similar to that of other locators. The valve positioner features a 4-20mA feedback control regulating element and a potentiometer. The 4-20mA feedback control regulating element consists of an INPUT terminal for connecting the 4-20mA control signal, wiring terminals, a SUPPLY terminal for connecting to a 24VDC DC power source, and 4 interfaces; a wire needs to be connected to each of these components. A potentiometer, also known as a knob resistor, can be used to detect the actual angular displacement of a positioner. Each component in the instrument has its own function, and these components complement each other with clear divisions of labor, thereby enabling the full advantage of the locator’s performance. Operation principle of the valve positioner: As the input current (DC4~20mA) increases, through the input processing circuit, calculation processing circuit, and output processing circuit on the substrate, the current flowing into coil 0 of the torque motor changes, causing armature 0 to swing around plate spring 0 as a pivot point. With this action, the gap between the nozzle and the baffle opens, and the back pressure inside the nozzle decreases. As a result, the exhaust spool in the pilot valve moves to the right, the pressure on the OUT1 side rises, and the diaphragm valve operates. The operation of the diaphragm valve is transmitted to the displacement output processing circuit on the substrate via the feedback shaft 0, angle sensor 0, and feedback lever; through computational processing, the output current is made to match the position of the input current. The above has introduced the components of valve positioners as well as their operating principles during use; I hope this will be helpful to you when utilizing them. Shanghai Mengyan Automation Equipment Co., Ltd. Address: Room 1119, Jiahong Building, No. 639 Guangfulin Road, Songjiang, Shanghai. Contact person: Xu Gong. Mobile phones: 18616582302 / 18616582330. QQ: 764861476. Email: sales@shmyzdh.com