MC-GDID83
在可变条件下使用自动控制
必须加以控制。在HVAC系统中
受控条件包括压力、温度、湿度和
流量。自动控制系统的应用范围
从简单的住宅温度调节到的温度调节
工业过程控制。
受控变量
自动控制要求系统中的
变量存在。自动控制系统控制
通过操纵第二个变量。第二个
变量，称为操纵变量，导致
受控变量的变化。
在通过热水盘管的空气加热的房间内
例如，恒温器测量温度（受控
规定温度下的室内空气（受控介质）的
地方当房间冷却时，恒温器操作一个阀门
调节热水流量（操纵变量）
（控制剂）通过线圈。这样，线圈就会
加热以加热室内空气。
控制回路，控制回路
在空调系统中，受控变量为
通过改变机械设备的输出进行维护
通过自动控制回路。控制回路包括
输入传感元件，如温度传感器；一
处理输入信号并产生输出的控制器
信号以及终控制元件，如阀门
根据输出信号。

Automatic controls are used wherever a variable condition must be controlled. In HVAC systems, the most commonly controlled conditions are pressure, temperature, humidity, and rate of flow. Applications of automatic control systems range from simple residential temperature regulation to precision control of industrial processes. CONTROLLED VARIABLES Automatic control requires a system in which a controllable variable exists. An automatic control system controls the variable by manipulating a second variable. The second variable, called the manipulated variable, causes the necessary changes in the controlled variable. In a room heated by air moving through a hot water coil, for example, the thermostat measures the temperature (controlled variable) of the room air (controlled medium) at a specified location. As the room cools, the thermostat operates a valve that regulates the flow (manipulated variable) of hot water (control agent) through the coil. In this way, the coil furnishes heat to warm the room air. CONTROL LOOP In an air conditioning system, the controlled variable is maintained by varying the output of the mechanical equipment by means of an automatic control loop. A control loop consists of an input sensing element, such as a temperature sensor; a controller that processes the input signal and produces an output signal; and a final control element, such as a valve, that operates according to the output signal.