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系统中的电气元件、电子元件以及模件的电磁相容性越来越显得重要。在设计和制造这样的设备的时候,必须考虑它们对其他信号引起的电磁干扰问题。测量设备和科学仪器现在的问题:(i)越来越灵敏并且响应速度越来越快;(ii)不得不在被宽频率范围及大幅度电磁噪声“污染”了的环境中工作;(iii)甚而要受仪器本身有源、无源元件和模件高密度排列的影响。尽管如此,仍然要求这些仪器能满意地工作,以探测或测量信号,即待测的量。本文将讨论有助于达到这一目的措施。但是,不仅环境影响仪器,仪器内部的信号干扰源(线路变压器、时钟脉冲线路、可控硅整流元件、开关等)也同样影响仪器。在仪器的机械设计和电路设计中就不得不考虑这些因素,以避免或减少干扰的影响。本文不讨论对仪器或其组件具有破坏性的那些影响(如雷击或仪器内部的静电放电等),仅讨论其影响可以复原的电学量。要解决干扰问题以进行精确测量,首先要对系统进行分析并定义“干扰敏感性”或称“灵敏度”。只要所需信号和干扰信号的频率范围差别很大,即使干扰信号是高电平的,也能很容易将其分离。可是,如果噪声即使很低但频带很宽(高斯噪声),或要探测的是处于高斯噪声或不规则噪声中的脉冲,那就很难区分信号和噪声了。对于后一种情况,系统理论的原则、信号理论和信息论都有助于解决问题而被广泛应用,本文不讨论这些问题。本文讨论的是在测量过程中有效地减小或避免仪器受到干扰影响的一般原则和方法。在本文中,解决这一问题的步骤是:(i)找出可能的干扰源;(ii)确定所需信号和干扰信号之间耦合的类型;(iii)找出能抑制干扰信号(在信号源处)的测量方法;(iv)能减小仪器内部(在干扰信号汇处)干扰影响的测量方法。这些方法包括:(a)机械设计方面(组件的布局排列、屏蔽);(b)电路设计方面(平衡、滤波、屏蔽、接地、使用高共模抑制的差分放大器,等等);(c)其他方法(网状屏蔽、极状屏蔽、绞绕导线)。
Electromagnetic compatibility of electrical components, electronic components and modules in the system is becoming more and more important. In the design and manufacture of such devices, they must consider the electromagnetic interference caused by other signals. (Ii) have to work in an environment that is “polluted” by a wide range of frequencies and substantial electromagnetic noise; (iii) Even by the instrument itself active, passive components and modules high-density arrangement. However, these instruments are still required to work satisfactorily to detect or measure signals, ie quantities to be measured. This article will discuss measures that will help achieve this goal. However, not only environmental impact instruments but also signal interference sources (line transformers, clock lines, thyristor elements, switches, etc.) within the instrument also affect the instrument. These factors have to be considered in the mechanical design and circuit design of the instrument to avoid or reduce the effects of interference. This article does not discuss those effects that can have destructive effects on the instrument or its components (such as lightning strikes or static discharges inside the instrument), but discusses the amount of electrical energy that can affect recovery. To solve the interference problem for accurate measurements, the system is first analyzed and the “interference sensitivity” or “sensitivity” defined. As long as the desired signal and the frequency range of the interfering signal vary widely, they can be easily separated even if the interfering signal is high level. However, if the noise is low, but the band is very wide (Gaussian noise) or if it is to detect pulses that are in Gaussian noise or irregular noise, then it is hard to tell the difference between the signal and the noise. For the latter case, the principles of system theory, signal theory and information theory are all helpful to solve the problem and are widely used. This article does not discuss these problems. This article discusses the general principles and methods for effectively reducing or avoiding instrument interference during measurement. In this paper, the steps to solve this problem are: (i) to identify possible sources of interference; (ii) to determine the type of coupling between the wanted signal and the interfering signal; (iii) to find out what type of interfering signal Source); (iv) Measurement methods that reduce the effects of interference inside the instrument (at the confusion of signals). These methods include: (a) mechanical design (layout of components, shielding); (b) circuit design (balancing, filtering, shielding, grounding, differential amplifier using high common mode rejection, etc.); Other methods (mesh shield, pole shield, twisted wire).