Series resonance? Wuhan UHV specializes in producing series resonators, with a wide range of product options. When looking for series resonators, choose Wuhan UHV.         

In order to deepen everyone's understanding of series resonance, and to comprehend the physical significance and measurement methods of circuit quality factor and passband, and to master the measurement methods of resonance frequency. Today, we will briefly discuss the experimental principles and methods of series resonance, as well as the issues that should be noted. 

Principle of series resonance test

The RLC series circuit is shown in the figure, and changing the circuit parameters L, C or power frequency may cause resonance in the circuit.       

The impedance of this circuit is a function of the power angular frequency ω: Z=R+j (ω L-1/ω C). When ω L-1/ω C=0, the current in the circuit is in phase with the excitation voltage, and the circuit is in a resonant state. The resonant frequency is only related to the values of the components L and C, and is independent of the resistance R and the angular frequency ω of the excitation power supply. When ω<ω 0, the circuit is capacitive and the impedance angle φ<0; When ω>ω 0, the circuit is inductive and the impedance angle is greater than 0.

Test method for series resonance

1. Method for measuring the resonant frequency f0 of a circuit.  

Method 1: Maintain the output amplitude of the signal source constant, gradually increase the frequency of the signal source from small to large, measure the voltage UR at both ends of R. When the reading of UR is maximum, the frequency value read is the resonant frequency f0 of the circuit.  

Method 2: Based on the characteristic that the input signal and resistance voltage have the same phase when the circuit resonates, connect these two signals to the two channels of the oscilloscope and set the oscilloscope to X-Y mode. By adjusting the signal frequency of the input signal generator, an ellipse with varying pole distances can be seen on the oscilloscope. When the ellipse becomes a straight line, the circuit resonates, and the frequency of the input signal is the resonant frequency.  

2. Measurement and monitoring of frequency characteristic curve composition

Measure the circuit, use an AC millivolt meter to measure the voltage, and monitor the signal source output with an oscilloscope to ensure that the output voltage US is ≤ 3V and remains constant. On both sides of the resonance point, take 8 measurement points in sequence, increasing or decreasing the frequency by 500Hz to 1kHz, and measure the values of I, UR, UL, Uc. point by point. Draw a curve based on the data.  

3. Measurement of quality factor Q of circuit circuit

Measure the output voltage US of the signal source and the inductance voltage UL when the circuit resonates, and calculate the quality factor Q of the circuit according to equation 7.2.

4. Measurement of current resonance curve

Keeping the voltage of L, C, and signal source constant in the circuit, changing the value of R will result in different Q values. Measure the current resonance curve under different Q values.  

Precautions for series resonance test

1. The selection of frequency points should take several points near the resonant frequency, and the maximum value point in frequency characteristics should not be missed.   

2. Before conducting frequency conversion testing, the signal output amplitude should be adjusted (monitored with an oscilloscope) to maintain a constant value. Before measuring UC and UL values, the measurement limit of the millivolt meter should be increased by approximately 10 times. When measuring UC and UL, the "+" terminal of the millivolt meter should be connected to the common point of C and L, and its grounding terminals should be taken as the near ground terminals of L and C, respectively.  

Through the series resonance test of Wuhan UHV, we can draw a conclusion that the series resonance circuit is current resonance and generally plays a role in current amplification. Amplify weak current signals through series resonance.