MU-TDOD23
自供电系统是一种相对较小但仍然重要的控制类型。这些系统使用测量变量的幂来诱导必要的纠正措施。例如，传感器处的温度变化会导致压力或体积变化，这些变化直接作用于阀门或阻尼器致动器中的隔膜或波纹管。许多完整的控制系统使用上述类别的组合。组合系统的一个示例是空气处理器的控制系统，该系统包括风扇的电气开/关控制以及加热和冷却盘管的气动控制。本手册以下章节介绍了各种控制方法：-气动控制基础知识。-电气控制基础-电子控制基础-基于微处理器/DDC基础。请参见控制方法的特征和属性。模拟和数字控制传统上，模拟设备执行HVAC控制。典型的模拟HVAC控制器为气动型，可连续接收数据并对其进行操作。在气动控制器中，传感器向控制器发送连续的气动信号，其压力与被测变量的值成比例。控制器将传感器发送的空气压力与设定点确定的所需空气压力值进行比较，并根据比较结果发出控制信号。

Self-powered systems are a comparatively minor but still important type of control. These systems use the power of the measured variable to induce the necessary corrective action. For example, temperature changes at a sensor cause pressure or volume changes that are applied directly to the diaphragm or bellows in the valve or damper actuator. Many complete control systems use a combination of the above categories. An example of a combined system is the control system for an air handler that includes electric on/off control of the fan and pneumatic control for the heating and cooling coils. Various control methods are described in the following sections of this manual: — Pneumatic Control Fundamentals. — Electric Control Fundamentals. — Electronic Control Fundamentals. — Microprocessor-Based/DDC Fundamental. See CHARACTERISTICS AND ATTRIBUTES OF CONTROL METHODS. ANALOG AND DIGITAL CONTROL Traditionally, analog devices have performed HVAC control. A typical analog HVAC controller is the pneumatic type which receives and acts upon data continuously. In a pneumatic controller, the sensor sends the controller a continuous pneumatic signal, the pressure of which is proportional to the value of the variable being measured. The controller compares the air pressure sent by the sensor to the desired value of air pressure as determined by the setpoint and sends out a control signal based on the comparison.