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(三)开环对数幅频L(ω)、对数相频特性φ(ω)与系统品质间的联系多数情况下,频率特性是用对数幅频、对数相频特性来表示的,这是由于它运算简单,绘制方便,便于系统的分析与综合。为了应用对数幅频圆图必须先将开环对数幅频、对数相频特性变换为开环对数幅相特性,之后再求出20lgA(ω)并评价品质,显然较麻烦。根据下述四点结论我们可由开环对数幅频、对数相频特性直接评价系统品质,这些结论可由前面讨
(C) Open-loop logarithm L (ω), the relationship between the logarithm phase frequency characteristics φ (ω) and system quality In most cases, the frequency characteristics are expressed in logarithmic amplitude frequency, logarithmic phase frequency characteristics This is because it is simple, easy to draw, easy to analyze and synthesize the system. In order to apply the logarithmic amplitude-frequency circle diagram, the open-loop logarithm amplitude and logarithmic phase-frequency characteristics must first be transformed into the open-loop log-phase amplitude and phase characteristics. Afterwards, 20lgA (ω) is obtained and the quality is appraised. Obviously, it is troublesome. According to the following four conclusions, we can directly evaluate system quality by the open-loop logarithmic amplitude-frequency and log-phase-frequency characteristics. These conclusions can be obtained from the previous discussion