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一、失真仪测频原理和频率刻度盘校准失真仪一般采用文氏电桥基波抑制器,其线路简化如图1。当电桥对基波平衡时,aa′对基波而言无电压输出,即滤去基波。平衡条件为: 化简上式,取等式两边虚部相等和实部相等。并令C_1=C_2=C;R_1=R_2=R。则有ω=1/(RC)或f_0=1/(2πRC)(f_0称中心频率)(1) R_4=2R_3 (2) 进一步分析可知,相位平衡不影响中心频率。当“调谐”和“调相”满足(1)和(2)式时,从失真仪电压表最小示值读出失真度,其频率刻度盘上的示值就应该是被测信号的基波频率。如果被测信号为振动台上传感器的输出信号,此时失真仪的示值就是振动台的频率。
First, the distortion of the principle of frequency measurement and frequency dial calibration distortion instrument generally used Venturi bridge fundamental suppressor, the line simplified as shown in Figure 1. When the bridge on the fundamental balance, aa ’no voltage output for the fundamental, that is, filtered to the fundamental. The equilibrium condition is: Simplify the above formula, take the imaginary part of the equality on both sides and the real part is equal. And let C_1 = C_2 = C; R_1 = R_2 = R. (1) R_4 = 2R_3 (2) Further analysis shows that the phase balance does not affect the center frequency. When “tuning” and “phase modulation” satisfy (1) and (2), read the distortion from the minimum value of the distortion meter voltmeter, and the indication on the frequency dial should be the fundamental of the signal under test frequency. If the signal under test is the output signal from the sensor on the vibration stage, the indication of the distortion instrument at this moment is the frequency of the vibration stage.