基礎(chǔ)篇——閥門定位器介紹（中英文）
閥門定位器的功能
The Function of a Valve Positioner
閥門定位器是一種通過增加或減少執(zhí)行器上的空氣負載壓力來將閥門置于正確位置的設(shè)備。過程控制器不會直接向執(zhí)行器發(fā)送信號來移動閥門，而是閥門定位器會感知閥門的準確位置并與執(zhí)行器通信以移動閥門。
閥門定位器通常安裝在氣動執(zhí)行器的軛或頂殼上（用于線性控制閥），或軸的末端附近（用于旋轉(zhuǎn)控制閥）。對于任何一種設(shè)置，定位器都以機械方式連接到閥桿或閥軸。這樣可以將閥門的位置與控制器請求的位置進行比較。
Valve positioners are devices used to put a valve in the correct position by increasing or decreasing the air load pressure on the actuator. Instead of the process controller sending a signal directly to the actuator to move the valve, a valve positioner senses the exact position of the valve and communicates to the actuator to move the valve.
Valve positioners are usually mounted on the yolk or top casing of a pneumatic actuator (for linear control valves), or near the end of the shaft (for rotary control valves). For either set-up, the positioner is connected mechanically to the valve stem or valve shaft. This allows for the valve’s position to be compared with the position requested by the controller.
閥門定位器的類型
Types of Valve Positioners
閥門定位器有四種基本類型：氣動、電子、電動氣動和數(shù)字；這些類型根據(jù)定位器使用空氣還是電力來移動執(zhí)行器而有所不同。
? 氣動裝置發(fā)送和接收氣動信號。它們本質(zhì)安全，可以提供很大的力來關(guān)閉閥門。
- 單作用或三通氣動定位器只向單作用閥門執(zhí)行器的一側(cè)送氣并從一側(cè)排氣，該執(zhí)行器由范圍彈簧對置。
- 雙作用或四通氣動定位器從執(zhí)行器的兩側(cè)送氣和排氣。
? 電動閥門定位器發(fā)送和接收電信號。有三種電動驅(qū)動類型：單相和三相交流 (AC) 和直流 (DC) 電壓。
? 電動氣動閥門定位器將電流控制信號轉(zhuǎn)換為等效的氣動信號。它們使用電和空氣的混合物。
? 數(shù)字或“智能”設(shè)備使用微處理器來定位閥門執(zhí)行器并監(jiān)控和記錄數(shù)據(jù)。它們非常精確，比模擬定位器消耗更少的空氣，并允許在線數(shù)字診斷。
There are four basic types of valve positioners: pneumatic, electronic, electro-pneumatic, and digital; these differ based on whether the positioner uses air or electricity to move the actuator.
? Pneumatic devices send and receive pneumatic signals. They are intrinsically safe and can provide a large amount of force to close a valve.
- Single-acting or three-way pneumatic positioners send air to and exhaust air from only one side of a single-acting valve actuator that is opposed by a range spring.
- Double-acting or four-way pneumatic positioners send and exhaust air from both sides of the actuator.
? Electric valve positioners send and receive electrical signals. There are three electric actuation types: single-phase and three-phase alternating current (AC), and direct current (DC) voltage.
? Electro-pneumatic valve positioners convert current control signals to equivalent pneumatic signals. They use a mixture of electricity and air.
? Digital or “smart” devices use a microprocessor to position the valve actuator and monitor and record data. They are very accurate, use less air than analogue positioners, and allow for online digital diagnostics.
使用閥門定位器的原因
Reasons to Use a Valve Positioner
為什么可能選擇在應用中使用閥門定位器？以下是五個原因：
? 更精確的控制：由于閥門定位器知道閥門的確切位置，因此它們提供比單獨使用執(zhí)行器所能實現(xiàn)的更精確的控制。
? 更快的控制：定位器可幫助控制閥更快地響應過程變量的變化，從而更大限度地減少系統(tǒng)在設(shè)定點以上或以下運行的時間。
? 一致的閥門位置：閥門兩端的壓差變化可能表明控制回路不穩(wěn)定。定位器是幫助穩(wěn)定閥門位置的一種解決方案。
? 更靈活的配置和功能：定位器允許在控制器和控制閥之間留出距離。
? 更大限度地減少摩擦的影響。閥桿填料中的摩擦會導致滯后和死區(qū)，從而降低生產(chǎn)率。
Why might you elect to use a valve positioner in your application? Here are five reasons:
? More accurate control: Since valve positioners know the valve’s exact position, they provide more precise control than can be achieved by an actuator on its own.
? Faster control: Positioners help control valves respond faster to changes in the process variable, minimizing the amount of time the system is operating above or below the setpoint.
? Consistent valve position: Varying differential pressure across the valve can indicate instability in the control loop. A positioner is one solution to help stabilize valve position.
? More flexible configurations and functions: A positioner allows you to put distance between the controller and the control valve.
? Minimize the effects of friction. Friction in the valve stem packing contributes to both hysteresis and deadband, which reduce productivity.
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