Inductors in DC Circuits

Electric Circuits Lab

Inductors in DC Circuits

I. Objectives:

After completing this lab experiment, you should be able to:

· Measure the resistance and Inductance.

· Use the Oscilloscope and Function generator.

· Measure the LR time constant using VR and VL.

· Understand the effect of series and parallel inductors on LR time constant.

II. Parts List:

· Resistor (1) 5.1 kΩ

· Inductor (2) 100mH

III. Procedures:

Part I:

1. Construct the circuit shown in Figure 1 in Multisim. (You may use either the clock voltage component or the function generator.)

PP

Figure 1: RL Circuit

2. Connect Channel A of the oscilloscope across the resistor and Channel B across the inductor.

3. Set the voltage source to 5VPP; 300 Hz, Square wave, 50% duty cycle

4. You should be able to see the waveform as shown below. (Use Volts/Div and Time/DIV settings to adjust the signal)

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Figure 2. Voltage across the inductor and resistor

5. Calculate the time constant of an LR circuit. Record the result in Table 1 below under the calculated value.

 = L/R

Calculated value

Measured value using VL

Measured value using VR

Time constant ()

19.6 us

20.319 us

20.398 us

Table 1: Calculated and measured time constant values

6. Turn on the cursors on the oscilloscope

7. Measuring the time constant with VL: (shown in Figure 3)

i. Set Channel A to “0” to turn off Channel A signal.

ii. Measure the peak value of the voltage across the resistor, by placing one of the cursors at the peak point _____5.002 V____.

iii. Calculate the 37% of the above value ___1.85V______.

iv. Place the second cursor at the voltage calculated above in step (iii).

v. Observe the change in time (T2-T1) value on the scope, which is the value of one time constant.

vi. Record the T2-T1 value in Table 1 above under measured value using VL.

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Figure 3: Measuring RL time constant using VL example (L = 150 mH)

Note: your scope screen will be different

8. Set Channel B to “0” to turn it off.

9. Set Channel A to “AC”

10. Adjust the Trigger settings, if needed, and you should be able to see the waveform as shown below. (Use Volts/Div and Time/DIV knobs to adjust the signal)

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Figure 4: Voltage across the resistor

11. Measuring the time constant: (shown in Figure 5)

i. Measure the peak value of the signal, by placing one of the cursors (T1) at the peak point and the other cursor (T2) at the negative peak. Calculate the total peak-to-peak voltage (T1-T2) _4.998V________.

ii. Calculate the 63% of the above value __3.15V_______.

iii. Place the second cursor (T2) at the negative peak value plus the step (ii) value above .

iv. Place T1 at the negative peak just before the signal begins to rise.

vii. Observe the dT (T2-T1) value on the scope, which is one time constant.

viii. Record the result in Table 1 above under measured value using VR.

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Figure 5: Measuring RL time constant using VR example (L = 150 mH)

Note: your scope screen will be different

Part II:

12. Place two inductors in series as shown below.

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Figure 6: Series Inductors

13. Calculate the total inductance value and record the results in Table 2 (Calculated) below.

14. Measure the total inductance value. (If you have the proper measuring device to do so). Use the following procedure to measure the inductance in Multisim if you do not have the proper measuring device.

i. Connect the Impedance Meter (Simulate >>Instruments>>LabView Instruments>>Impedance Meter) as shown in Figure 7.

ii. Measure the inductive reactance, XL, as shown in Figure 7 .

iii. Calculate the inductance using the equation. and record the value in Table 2 (Measured).

Calculated Value

Measured Value

Inductance

200

199.99

Table 2: Series Inductors

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Figure 7. Impedance Meter in Multisim Example

15. Build the circuit in Figure 8.

Figure 8: RL circuit with series Inductors

16. Calculate the new LR time constant. Record the result in Table 3 below.

17. Connect Channel A of the oscilloscope across the resistor.

18. Adjust the Trigger, if needed, and you should be able to see the waveform as shown below. (Use Volts/Div and Time/DIV knobs to adjust the signal)

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Figure 9: Voltage across the resistor

19. Use the cursors on the oscilloscope to measure the time constant (refer to step 11). Record the result in Table 3 below under measured value.

Calculated value

Measured value using VR

Time constant ()

40 us

41.276 us

Table 3: Calculated and measured time constant values

Part III:

20. Place two inductors in parallel as shown below. ( Note: The 0.001 Ω resistor is ONLY required for simulation in Multisim. Without the resistor, the mathematical model will not converge.)

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Figure 10: Parallel Inductors

21. Calculate the total inductance value and record the results in Table 4 (Calculated).

Calculated value

Measured value

Inductance

50

50

Table 4: Parallel Inductors

22. Measure the total parallel inductance value. (If you have the proper device to do so). Use the following procedure to measure the inductance in Multisim if you do not have the proper measuring device.

i. Connect the Impedance Meter (Simulate >>Instruments>>LabView Instruments>>Impedance Meter).

ii. Measure the inductive reactance, XL 18.8496 .

iii. Calculate the inductance using the equation and record the value in Table 4 (Measured).

23. Build the following circuit. ( Note: The 0.001 Ω resistor is ONLY required for simulation in Multisim. Without the resistor, the mathematical model will not converge.)

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Figure 11: RL circuit with parallel Inductors

24. Calculate the new LR time constant. Record the result in Table 5 below.

25. Connect Channel A of the oscilloscope across the resistor.

26. You should be able to see the waveform as shown below. (Use Volts/Div and Time/DIV knobs to adjust the signal)

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Figure 12: Voltage across the resistor

27. Use the cursors on the oscilloscope to measure the time constant (refer to step 11). Record the result in Table 5 below under measured value