1C31233G04模块备件

1C31233G04

概述
本节讨论Ovation系统中电气噪声的原因，以及
消除或减少噪声的推荐技术。
本节包括以下主题：
•背景（第2-2节）
•噪声识别（第2-3节）
•噪声源（第2-4节）
•噪声等级（第2-5节）
•噪声抑制（第2-6节）
•模拟信号屏蔽技术（第2-7节）
•常见输入注意事项（第2-8节）
2-2.背景
各种模拟和/或数字电路与Ovation相关
系统的安装。有低电平电压电路，高电平电压
电路、传输信息的电路和传输功率的电路。这些
电路分为两类：噪声产生电路和噪声敏感电路
电路。
噪声问题通常发生在传输模拟（电压、电流和
其他测量值）或数字信息（开/关条件、脉冲串或
类似数据）通过互连或有线电路传输。所携带的信息
此类电路中的信号可能在传输过程中失真，并可能导致错误
从这种失真中。
传输信息的信号与该信息的信号之间的差异
接收到的信息称为噪声（见图2-1和图2-2）。噪音
本节简要介绍的小化技术侧重于防止错误
通过消除噪声，或在无法消除噪声时，执行
减少其影响的步骤。
噪声小化技术
R3-1150（第3版）2-2 2/03
艾默生过程管理专有2C类
2-3.噪声识别
自然信号特性（如数字信号的峰值）或产生的条件
在信号传输期间（如模拟信号的电压），用于：
使信号中的所需信息看起来不同于噪声。这个
因此，从噪声信号中恢复正确信息取决于
从所需信息中减去噪声的能力。
信号有三个分量可用于分离所需信号：
来自噪声信号的信息：
•能级
•频率
•来源（信号和噪声）
以下各页解释了如何将这些组件应用于：
小化可能由于噪声信号而发生的误差。
2-3.1.能级
能级是信号的总能量加上任何感应噪声。如果有
信号和噪声之间的显著差异，则噪声被拒绝
很容易通过阈值技术（如图2-1所示）。如果有
如果信号和噪声之间没有显著差异，则噪声不是
容易被拒绝（如图2-1所示为不需要）。
图2-1.振幅辨别示例
完美的
信号
完美的
信号
严峻的
噪音
征税
信号
加
噪音
不受欢迎的
噪声和信号不足
振幅对比度允许简单
阈值鉴别

1C31233G04

1C31233G04

Overview This section discusses the causes of electrical noise in your Ovation system and the recommended techniques for eliminating or reducing that noise. The following topics are included in this section: • Background (Section 2-2) • Noise Discrimination (Section 2-3) • Noise Sources (Section 2-4) • Noise Classes (Section 2-5) • Noise Rejection (Section 2-6) • Analog Signal Shielding Techniques (Section 2-7) • Common Input Considerations (Section 2-8) 2-2. Background A wide variety of analog and/or digital circuits are associated with the Ovation System’s installation. There are low-level voltage circuits, high-level voltage circuits, circuits that transfer information, and circuits that transfer power. These circuits are placed into two categories: noise-producing circuits and noise-sensitive circuits. Noise problems typically occur when transmitting analog (voltage, current, and other measured values) or digital information (on/off conditions, pulse trains or similar data) via inter-connected or wired circuits. The information carried by signals in such circuits may become distorted during transfer and errors may result from this distortion. The difference between the signal of transmitted information and the signal of that information as received is called noise (see Figure 2-1 and Figure 2-2). The noise minimization techniques briefly described in this section focus on preventing errors by either eliminating the noise, or when elimination is not possible, performing steps to lessen its impact. Noise Minimization Techniques R3-1150 (Rev 3) 2-2 2/03 Emerson Process Management Proprietary Class 2C 2-3. Noise Discrimination Natural signal properties (such as the peaks of a digital signal) or conditions created during signal transmission (such as the voltage of the analog signal) are used to make the desired information in the signal appear different from the noise. The recovery of correct information from a noisy signal therefore depends upon the ability to subtract the noise from the desired information. There are three components of a signal that can be used to separate the desired information from a noisy signal: • Energy Level • Frequency • Source (of both Signal and Noise) The following pages explain how each of these components can be applied to minimize errors that may occur because of a noisy signal. 2-3.1. Energy Level The energy level is the total energy for the signal plus any induced noise. If there is a significant difference between the signal and the noise, then the noise is rejected easily by thresholding techniques (as identified as Desirable in Figure 2-1). If there is not a significant difference between the signal and the noise, then the noise is not easily rejected (as identified as Undesirable in Figure 2-1). Figure 2-1. Amplitude Discrimination Example Ideal Signal Ideal Signal Severe Noise Imposed Signal plus Noise Undesirable The noise and signal have insufficient amplitude contrast to permit simple threshold discrimination