基础篇——阀门定位器介绍（中英文）

阀门定位器的功能

The Function of a Valve Positioner

阀门定位器是一种通过增加或减少执行器上的空气负载压力来将阀门置于正确位置的设备。过程控制器不会直接向执行器发送信号来移动阀门，而是阀门定位器会感知阀门的准确位置并与执行器通信以移动阀门。

阀门定位器通常安装在气动执行器的轭或顶壳上（用于线性控制阀），或轴的末端附近（用于旋转控制阀）。对于任何一种设置，定位器都以机械方式连接到阀杆或阀轴。这样可以将阀门的位置与控制器请求的位置进行比较。

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.

阀门定位器的类型

Types of Valve Positioners

阀门定位器有四种基本类型：气动、电子、电动气动和数字；这些类型根据定位器使用空气还是电力来移动执行器而有所不同。

• 气动装置发送和接收气动信号。它们本质安全，可以提供很大的力来关闭阀门。

- 单作用或三通气动定位器只向单作用阀门执行器的一侧送气并从一侧排气，该执行器由范围弹簧对置。

- 双作用或四通气动定位器从执行器的两侧送气和排气。

• 电动阀门定位器发送和接收电信号。有三种电动驱动类型：单相和三相交流 (AC) 和直流 (DC) 电压。

• 电动气动阀门定位器将电流控制信号转换为等效的气动信号。它们使用电和空气的混合物。

• 数字或“智能”设备使用微处理器来定位阀门执行器并监控和记录数据。它们非常精确，比模拟定位器消耗更少的空气，并允许在线数字诊断。

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.

使用阀门定位器的原因

Reasons to Use a Valve Positioner

为什么可能选择在应用中使用阀门定位器？以下是五个原因：

• 更精确的控制：由于阀门定位器知道阀门的确切位置，因此它们提供比单独使用执行器所能实现的更精确的控制。

• 更快的控制：定位器可帮助控制阀更快地响应过程变量的变化，从而更大限度地减少系统在设定点以上或以下运行的时间。

• 一致的阀门位置：阀门两端的压差变化可能表明控制回路不稳定。定位器是帮助稳定阀门位置的一种解决方案。

• 更灵活的配置和功能：定位器允许在控制器和控制阀之间留出距离。

• 更大限度地减少摩擦的影响。阀杆填料中的摩擦会导致滞后和死区，从而降低生产率。

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.