The Tuned Circuit. Aim of the experiment. Circuit. Equipment and components. Display of a decaying oscillation. Dependence of L, C and R.

Transcription

1 The Tuned Circuit Aim of the experiment Display of a decaying oscillation. Dependence of L, C and R. Circuit Equipment and components 1 Rastered socket panel 1 Resistor R 1 = 10 Ω, 1 Resistor R 2 = 1 kω 2 Capacitors C 1, C 2 = 0.1 µf 1 Capacitor C k = 4.7 nf 1 Capacitor C p = 10 nf 1 Coil, 500 turns, 1 Transformer core 1 Function generator 1 Oscilloscope 2 Sets of probes Bridging plugs, Connecting leads 1

2 Conducting the experiment Part 1 1. Assemble the measuring circuit. 2. Function generator: f = 100 Hz (square - wave) U 1 approx. 5 V pp Apply this signal to the differentiator (R 2 C 1 ). At the output spike pulses will appear with positive leading and negative trailing edges, which excite the tuned circuit. Oscilloscope: Y 1 (5 V/cm) first connected to the square-wave signal and then to the spike signal. Time base: 1 ms/cm; AT Y 2 (100 mv/cm) connected to the tuning circuit. Coil without iron core. Short-circuit R 1 = 10 Ω. 3. You should get the following graph. Make a true-to-scale drawing. Part 2 4. Adjustments as in part 1, but slowly insert the core into the coil. Observe the 1 frequency of the decaying oscillation. T 2

3 Part 3 5. Adjustments as in part 2, but connect a capacitor C p = 10 nf in parallel to C 2. Part 4 6. Adjustments as in part 3, but remove the core, and also remove the shortcircuit across the resistor R 1 = 10 Ω. When doing so, observe the decaying oscillation. 3

4 Parallel Resonant Circuit Aim of the experiment Measuring the resonance frequency and displaying the resonance curve. Changing the resonance frequency Measuring the phase of the inductive and capacitive reactive current with respect to the resonance voltage Measuring bandwidth and Q Circuit Equipment and components 1 Rastered socket panel 1 Resistor R 1 = 10 Ω 1 Capacitor C = 0.1 µf 1 Capacitor C k = 4.7 nf 1 Capacitor C p = 10 nf 1 Coil, 500 turns, 1 Transformer core 1 Function generator, 1 Oscilloscope 2 Sets of probes Bridging plugs, Connecting leads 4

5 Conducting the experiment Part 1 1. Set U 1 = 2 V pp (sine). Measuring point A (Y 1 : 1 V cm ). 2. Assemble the circuit without the resistor R = 10 Ω (short circuit), and without inserting the iron core into the coil. 3. Connect Y 2 (1 V cm, 10:1) to the point of C k, L, C = measuring point B ( hot point of the circuit). 4. Change the frequency until a voltage maximum is observed at Y 2. Read off the frequency.(this is the resonant frequency f res of the parallel-tuned circuit). f res = U res = Part 2.A Measuring the resonant curve. 5. Connect Y 1 (200 mv cm Set U 1 to U res = 1.2 V pp (6 divisions.). ) to measuring point B. 6. Measure the output for frequencies above and below the resonance frequency. 7. Tabulate the results and draw a graph. In order to characterize a tuned circuit, those frequencies above and below the resonance frequency are important where the voltage has dropped to: U res 2 = U res. f/ khz U 2 / V pp 5

6 Part 2.B 8. Repeat the measurement with R = 10 Ω connected in series to the coil. f/ khz U 2 / V pp Make a diagram of both curves with U 2 = Function of frequency F (f) Exercise Measure the band width (b), where b = 2 Δf b = Measure the quality factor Q which is defined as the ratio between: resonance frequency band width = f res 2Δf = Q Q = Part 3 9. Adjust the frequency of the generator to f = 5 khz (2 V pp ). 10. Connect Y 2 (0.5 V cm, 10 : 1) to measuring point B and trigger on Y Remove Y 1. Slowly insert the iron core and see if a maximum can be obtained: U res = Part Connect the capacitor C p = 10 nf in parallel to the capacitor C = 0.1 µf and retune the frequency for maximum: f res = U res = 6

7 Series Resonant Circuit Aim of the experiment Measure the course of the voltages across the resistor, the coil and the capacitor as a function of the frequency Measure bandwidth, and quality factor Circuit Equipment and components 1 Rastered socket panel 1 Resistor R = 10 Ω 1 Capacitor C = 0.1 µf 1 Coil, 500 turns, 1 Transformer core 1 Function generator, 1 Oscilloscope 2 Sets of probes Bridging plugs, Connecting leads 7

8 Conducting the experiment Measure the voltages across the resistor: U R. Measure the voltages across the capacitor: U C. Measure the voltages across the coil: U L. With U 1 = 2 V pp f khz U R mv pp U L V pp U C V pp Make a diagram of U R, U L and U C. Exercises Calculate the band width b : b = 2Δf = Calculate the quality factor Q : Q = f res 2Δf = 8