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当现场的测量信号送入计算机或仪表系统进行控制或数据处理时,由于各种干扰,会引起测量信号严重失真,采用本文介绍的这种实用电路可以使设计出的智能仪器性能更加稳定、可靠。例如,由该电路构成的一种微波电子测量仪器如雷达测速仪,目前已用于公路、铁路及其它需要测速、限速的场所,受到了国内外用户的欢迎。该电路组成框图见图1。电路中,低通滤波部分的作用是只允许1.2kHz以下的信号频率通过,这个范围是我们所关心的。带自动增益控制的放大电路的作用是当输入信号快速变化时,确保一个恒定的电平输出;即当输入量增加时,输出量不增加或几乎不增加,使强信号饱和。这两个部分的电路图见图2。跟踪滤波电路能将噪声与信号分别开来,从而能容易地识别出信号,它是低频信号跟踪与提取的关键部分。图3所示是跟踪滤波电路的原理框图。
When the measured signal is sent to the computer or instrumentation system for control or data processing, due to various kinds of interference, the measured signal will be seriously distorted. The practical circuit described in this paper can make the smart instrument designed more stable and reliable . For example, a microwave electronic measuring instrument such as a radar gun made up of this circuit has been used in the places where the speed, speed and speed of roads, railways and other needs are currently used and has been well received by users both at home and abroad. The circuit block diagram shown in Figure 1. Circuit, the role of low-pass filter is only allowed to pass the signal frequency below 1.2kHz, this range is our concern. The amplifier circuit with automatic gain control ensures a constant level output when the input signal changes rapidly; that is, when the input level increases, the output signal does not increase or scarcely increases, saturating the strong signal. The two parts of the circuit shown in Figure 2. Tracking filter circuit can separate the noise and signal, which can easily identify the signal, which is the key part of the low-frequency signal tracking and extraction. Figure 3 shows the block diagram of the tracking filter circuit.