GT4503/A (microcomputer type) LCR circuit characteristics research experiment instrument manual

Research on LCR circuit characteristics

The impedance of a capacitor or an inductor in an AC circuit varies with the frequency of the power supply. When a sinusoidal AC voltage is applied to a circuit composed of a resistor, a capacitor, and an inductor, the voltage and phase of each component change. This is called the steady-state characteristic of the circuit; when a step voltage is applied to the circuit composed of LCR components, the state of the circuit changes from one equilibrium state to another, and the voltage on each component changes regularly. This is called the transient characteristic of the circuit.

[Purpose]

1. Observing the amplitude-frequency characteristics and phase-frequency characteristics of RC and RL series circuits

2. Understand the phase-frequency characteristics and amplitude-frequency characteristics of LCR series and parallel circuits

3. Observe and study the series resonance and parallel resonance phenomenon of LCR circuits

4. Observe the transient process of RC and RL circuits and understand the meaning of time constant Ï„

5. Observing the transient process of LCR series circuit and its damping oscillation

6. Understand and be familiar with the characteristics of half-wave rectification and bridge rectifier circuits and RC low-pass filter circuits.

[laboratory apparatus]

1, GT4503/A (microcomputer type) LCR circuit experiment instrument

2. Double trace oscilloscope

3, digital storage oscilloscope (optional)

[Experimental content]

The sinusoidal wave is used for the observation of the steady-state characteristics of the RC, RL, and LCR circuits. The DC power supply and the square wave signal can be used for the transient characteristics of the LCR circuit, and the square wave can be used as the test signal for convenient observation by an ordinary oscilloscope. When the signal is used for experimentation, a digital storage oscilloscope is needed to get better observation.

GT4503/A (microcomputer type) LCR circuit tester use and performance see the Appendix, the use of the oscilloscope refers to the manufacturer's instructions or the guidance of the experimental teacher. Note: the instrument uses an open design, the wiring should be correctly used, do not short circuit the power signal Source to prevent damage.

First, the steady state characteristics of the RC series circuit

1, the amplitude and frequency characteristics of the RC series circuit

Select the sine wave signal, keep its output amplitude unchanged, measure the UR and UC at different frequencies with the oscilloscope respectively, and take C=0.1μF, R=1KΩ, or choose the R and C parameters according to the actual situation.

When using a two-channel oscilloscope, one channel can be used to monitor the signal source voltage, and the other channel can measure UR and UC separately. However, it should be noted that the grounding point of the two channels should be at the same point of the line, otherwise some circuits will be short-circuited.

2. Phase frequency characteristics of RC series circuit

Connect the signal source voltage U and UR to the two channels of the oscilloscope respectively, which can be C=0.1μF, R=1KΩ (also optional). Adjust the signal source frequency from low to high to observe the phase changes of the two waveforms on the oscilloscope. It can be observed by Lissajous figure method and record the phase difference at different frequencies.

Second, the steady state characteristics of the RL series circuit

The amplitude-frequency characteristic and phase-frequency characteristic of the RL series circuit are similar to those of the RC serial circuit. L=10mH and R=1KΩ can be selected.

Third, the steady state characteristics of the LCR series circuit

Select the appropriate L value, C value and R value, use the two channels of the oscilloscope to measure the signal source voltage U and the resistance voltage UR. It must be noted that the common lines of the two channels are connected, and the access circuit should be at the same point, otherwise Will cause a short circuit.

1, amplitude and frequency characteristics

Keep the signal source voltage U constant (Upp=5V), estimate the resonant frequency according to the selected L and C values ​​to select the appropriate sine wave frequency range. Adjust the frequency from low to high, when the voltage of UR is maximum The frequency is the resonant frequency, recording the UR size at different frequencies.

2, phase frequency characteristics

Observe the phase difference of U with the two-channel oscilloscope. The phase of UR is the same as the phase of the current in the circuit. Observe the phase change at different frequencies and record the phase difference at a certain frequency.

Fourth, the steady state characteristics of LCR parallel circuit

Connect according to Figure 9. Note that R is the internal resistance of the inductor, which varies with the value of the different inductors. Its value can be measured with the DC resistance meter under the corresponding inductance value. Select L=10mH, C=0.1. μF, R' = 10KΩ. It can also be designed and selected by itself. Note that the value of R' should not be too small, otherwise it will affect the size of UR' due to the large change of total current in the circuit.

1. Amplitude-frequency characteristics of LC parallel circuit

Keep the U value of the signal source constant (take UPP 2~5V) and measure the change of U and UR'. Pay attention to the common terminal wiring of the oscilloscope, which should not cause short circuit.

2. Phase-frequency characteristics of LCR parallel circuit

Use the two channels of the oscilloscope to measure the phase change of U and UR'. Determine the circuit parameters by yourself.

V. Transient characteristics of RC series circuit

If the signal source is selected as DC voltage, observe the single charge process using a storage oscilloscope. We choose square wave as the signal source to conduct experiments to observe with ordinary oscilloscope. Because the power signal output is used, it should prevent short circuit.

1. Select the appropriate R and C values, and select the appropriate square wave frequency according to the time constant Ï„. Generally, the square wave period T>10Ï„ is required, which can completely reflect the transient process and select the appropriate oscilloscope scanning speed. To completely display the transient process.

2. Change the R value or C value, observe the variation law of UR or UC, record the waveform condition of different RC values, and measure the time constant Ï„ respectively.

3. Change the square wave frequency, observe the change of the waveform, and analyze the waveform change of the same Ï„ value at different frequencies.

Sixth, the transient process of the RL circuit

Select the appropriate L and R values, note that the value of R should not be too small, because L has internal resistance. If the waveform has distortion and self-excitation, the L value and R value should be re-adjusted for experiment, the method and RC series circuit The transient characteristics experiment is similar.

Seven, the transient characteristics of the LCR series circuit

1. Select the appropriate L and C values ​​first, and adjust the R value according to the selected parameters. Observe the waveforms of the three damped oscillations. If the number of oscillations is less than under damping, the L and C values ​​should be re-adjusted.

2. Using the oscilloscope to measure the under-oscillation period T and the time constant Ï„.Ï„ value reflect the attenuation speed of the oscillation amplitude. The time from the maximum amplitude attenuation to the maximum amplitude of 0.368 times is the Ï„ value.

Eight, the characteristics of the rectification filter circuit observation

1, half-wave rectification

Connect according to the principle of Figure 17, select the sine wave signal as the power supply. Do not connect the filter capacitor first, observe the waveform of U and Uo.

Then access the C value of different capacity. Observe the change of Uo waveform.

2, bridge rectifier

According to the principle of Figure 18, do not connect the filter capacitor, observe the Uo waveform, and then access the C value of different capacity. Observe the change of Uo waveform and compare with the half-wave rectification.

[data processing]

1. According to the measurement results, the amplitude-frequency characteristics and phase-frequency characteristics of the RC series circuit are taken.

2. According to the measurement results, the amplitude-frequency characteristics and phase-frequency characteristics of the RL series circuit are obtained.

3. Analyze the frequency characteristics of RC low-pass filter circuit and RC high-pass filter circuit.

4. According to the measurement results, the amplitude-frequency characteristics and phase-frequency characteristics of the LCR series circuit and the LCR parallel circuit are calculated. The Q value of the circuit is calculated.

5. According to different R values, C values ​​and L values, what is the difference between the transient response curves of the RC circuit and the RL circuit.

6. According to different R values, the transient response curve of LCR series circuit is made, and the influence of R value on charge and discharge is analyzed.

7. Make the output voltage waveform of half-wave rectification and bridge rectification according to the waveform of the oscilloscope, and discuss the influence of the value of the filter capacitor.

Appendix GT4503/A (Microcomputer Type) LCR Circuit Tester Technical Description

GT4503/A (microcomputer type) The LCR circuit experiment instrument adopts an open design, and the student's own connection to complete the study of the steady state and transient characteristics of the RC, RL, and LCR circuits, so as to grasp the first-order circuit and the second-order circuit. The response process of sine wave and step wave, and understand the working principle of integral circuit, differential circuit and rectifier circuit.

First, the instrument composition

The instrument consists of power signal generator, frequency meter, resistor box, inductor box, capacitor box and rectifier filter circuit, see the attached figure.

GT4503/A (microcomputer type) LCR circuit experiment instrument panel diagram

Second, the main technical parameters of the instrument

1, power supply: single phase 220V, 50Hz

2, the working temperature range is 5~35 °C, the relative temperature is 25~85%

3. Signal source:

Sinusoidal wave 50Hz~1KHz, 1K~10KHz, 10KHz~100KHz three bands

The square wave is 50Hz~1KHz, and the signal amplitude is adjustable from 0~6Vpp.

DC 2~8V adjustable

4, frequency meter working range: 0~99.999KHz, 5 digits display, resolution 1Hz

5. Decimal resistance box: (10KΩ +1KΩ+100 Ω+10Ω)×10, accuracy 0.5%

6, decimal inductor box: (10mH + 1mH) × 10, accuracy 2%

7. Decimal capacitor box: (0.1μF+0.01μF+0.001μF)×10, accuracy 1%

8, instrument dimensions: 400mm × 250mm × 120mm

Third, matters needing attention

1. Preheat the instrument for 10~15 minutes before use, and avoid strong magnetic field source or magnetic material around it.

2. The instrument adopts open design. It should be correctly wired when used. Do not short-circuit the power signal source to prevent damage. Turn off the power after use.

3, the use and storage of the instrument should be cleaned to avoid corrosion and sun exposure.

4. The warranty period of this instrument is one year.

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