1C31127G01模块备件

1C31127G01

噪声抑制
2-6.1.数字信号噪声抑制
Ovation系统采用三种特定的数字噪声抑制措施：
信号设备互连：
•低通滤波
•大量信号电平（48 VDC或115 VAC）
•隔离或光耦合
低通滤波和大信号电平技术的使用提供了频率和
分别是能级鉴别。
数字信号接收器与地面的隔离是一种重要的方法，用于：
抑制噪声，使信号对中的两条导线改变对地电压
电位。这种隔离的一个例子是信号源（变送器）
其在远离接收器的点处接地，其中发射器和
接收器接地电压不相同。在这种情况下，接地电位
差异表现为相应信号对的两根导线上的电压。
另一个可能需要隔离以拒绝接地电势的示例
差异噪声将出现在信号线之间存在耦合的电路中，
在两根导线中感应电势。当信号线
存在于电磁场或静电场变化的环境中。
在这种情况下，可能需要隔离。
光学隔离器（也称为光隔离器）可用于将数字
向接收器发送信号。除非信号线：
噪声电流流动。低频电流，可能由于以下原因而流动：
如果出现以下情况，则消除信号对两根导线上的噪声电压对地电位：
信号线的接地点不超过一个。这就是所谓的
共模电压。
笔记
高频噪声电流可通过杂散电流流动
电容作为其路径的一部分。这需要使用
除了光学滤波之外的低通滤波
隔离
噪声小化技术
R3-1150（第3版）2-6 2/03
艾默生过程管理专有2C类
2-6.2.模拟信号噪声抑制
提供模拟信号隔离的原因与所讨论的相同
数字信号（如第2-6节所述）。然而，由于模拟信号是
通常，低电平、滤波和隔离噪声抑制技术更多
模拟信号比数字信号更重要。
模拟信号滤波通过对一个周期（或
周期的整数倍）。电力线相关噪声，
在电力线频率及其谐波下，当
平均值正好在一个周期内取下，并由此从信号中滤出
技巧
瞬态噪声（高频阻尼振铃）的平均值为零
时间段内的平均值，比时间段的持续时间长得多

1C31127G01

1C31127G01

Noise Rejection 2-6.1. Digital Signal Noise Rejection The Ovation System employs three specific noise rejection measures for digital signal plant interconnections: • Low pass filtering • Substantial signal levels (48 VDC or 115 VAC) • Isolation or optical coupling Low pass filtering and the use of large signal level techniques provide frequency and energy level discrimination, respectively. Isolation of the digital signal receiver from ground is important as a means for rejecting noise which causes both wires in a signal pair to change voltage-to-ground potentials. An example of this type of isolation is a signal source (transmitter) which is grounded at a point remote from the receiver, where transmitter and receiver grounds are not at the same voltage. In this case, ground potential difference appears as a voltage on both wires of the corresponding signal pair. Another example in which isolation may be required to reject ground potential difference noise would be in circuits where coupling exists between signal wires, inducing a potential in both wires. Induced potentials can occur when signal wires are present in environments with changing electromagnetic or electrostatic fields. Isolation may be required in this case. An optical isolator (also known as an opto-isolator) may be used to bring digital signals into the receiver. No receiver response to noise can occur unless signal line noise current flows. Low frequency current, which may flow as a result of equal noise voltage-to-ground potentials on both wires of the signal pair, is eliminated if the signal wires are not grounded at more than one point. This is called the common-mode voltage. Note High frequency noise currents can flow using stray capacitance as part of their path. This requires the use of low pass filtering in addition to the optical isolation. Noise Minimization Techniques R3-1150 (Rev 3) 2-6 2/03 Emerson Process Management Proprietary Class 2C 2-6.2. Analog Signal Noise Rejection Analog signal isolation is provided for the same reasons that are discussed for digital signals (as described in Section 2-6). However, since analog signals are typically low level, filtering and isolation noise rejection techniques are more critical for analog signals than for digital signals. Analog signal filtering is achieved by averaging applied signals for one cycle (or an integer multiple of cycles) of the AC power line frequency. Power line related noise, at the power line frequency and its harmonics, has exactly zero average value when the average is taken over exactly one cycle and is filtered out of the signal by this technique. Transient noise (high frequency damped ringing) has zero average value for averages taken over time periods much longer than the duration of th