**Laboratory Procedures**

**DeVry University
College of Engineering and Information Sciences**

## I. OBJECTIVES

1. To simulate the operation of a series and parallel resonance circuit consisting of a resistor (R), an inductor (L), and a capacitor (C).

2. To plot the resonance curves of the simulated RLC circuit by varying the AC voltage source. frequency.

3. To build series and parallel RLC resonance circuit and to verify the results obtained by simulation.

## II. PARTS LIST

Equipment:

###### IBM PC or compatible

Function generator

DMM (digital multimeter)

Parts:

** **1 – 470 ? resistor 1 – 1 µF capacitor

1 – 47 mH inductor

Software:

MultiSim 11

## III. PROCEDURE

## A. Simulation of a Parallel Resonance Circuit

1. Construct the RLC parallel circuit shown in **Figure 1**. Simulate the circuit at the frequencies shown in Table 1. Note and record the current readings obtained in the table with switch S1 closed. This represents the inductor as an ideal inductor with zero wire resistance.

The inductor self-resistance, *R*L = 65 ?, has been included in the schematic after measuring the actual component. If the inductor you choose has different DC resistance, please feel free to modify the circuit.

2. Plot the data obtained above in the graph sheet below. Note: frequency should be on the *X*-axis; the source current ** IS (mA**) should be on

*Y*-axis.

Figure 1: Parallel Resonance Circuit

**Frequency, Hz**

*I***S**** (RMS), mA**

*I***C**** (RMS), mA**

*I***L**** (RMS), mA**

200

300

500

700

730

734

738

800

1000

1200

1400

**Table 1: Parallel Resonance Simulation with Switch S1 “OFF”**

** Plot 1 – Parallel Resonance Data**

3. Answer the questions below:

a)

What happens to the source current, *I*S, as the frequency is changed from low to high? Describe in your own words.

Answer:

b)

Did the source current, *I*S, go through a minimum or maximum as the frequency is changed from low to high?

Answer:

c)

What is the source frequency at the source current, *I*S, minimum? What do you call the frequency at that point?

Answer:

d)

What do you notice from the values of the currents *I*C and *I*L at *I*S minimum?

Answer:

e)

What is the phase relationship between *I*C and *I*L at *I*S minimum?

Answer:

f)

What happens to the total impedance, *Z*P, of the parallel circuit at the current minimum? Choose the correct answer below:

Answer:

i) OPEN Circuit ii) SHORT Circuit

g)

Why is the source current, *I*S, minimum at this frequency?

Answer:

4. Turn the switch J1 in the simulator to the OPEN condition. Vary the source frequency between 700 Hz to 734 Hz (in steps of 2 Hz) to obtain the minimum source current, *I*S. Note it and also record the frequency below.

New resonant frequency with the J1 switch OPEN = Hz.

5. Answer the questions below with the J1 switch open:

a)

What happened to the inductive branch of the circuit with the switch J1 OPEN?

Answer:

b)

Did the resonance frequency go UP or DOWN compared with the previous result? Circle the correct answer.

Answer:

c)

Calculate the Quality Factor, *Q* of the inductor at this resonance frequency.

*Q* = {?res L }/ *R*L

Answer:

**B****. ****Simulation of a Series Resonance Circuit**

1. Construct the RLC series resonance circuit shown in **Figure 2** in Multisim. Simulate the circuit at the frequencies shown in Table 2, and record the current readings obtained.

The inductor self-resistance, *R*L = 65 ?, has been included in the schematic. If the inductor you choose has different DC resistance, please feel free to modify the circuit.

Figure 2: Series Resonance Circuit

**Frequency, Hz**

*I***S**** (RMS), mA**

*V***C**** (RMS), mV**

*V***L**** (RMS), mV**

200

300

500

700

730

734

738

800

1000

1200

1400

**Table 2: Series Resonance Simulation**

2. Plot the data obtained above in the graph sheet below. Note: frequency should be on the *X*-axis; the source current ** IS (mA**) should be on

*Y*-axis.

3. Use the simulation results to answer the following questions:

a)

What happens to the source current, *I*S, as the frequency is changed from low to high? Describe in your own words.

Answer:

b)

What is the source frequency at the source current, *I*S, maximum? What do you call the frequency at that point?

Answer:

c)

What do you notice from the values of the voltages *V*C and *V*L at *I*S maximum?

Answer:

d)

What is the phase relationship between *V*C and *V*L at *I*S maximum?

Answer:

e)

What happens to the total impedance, *Z*S, of the series L and C part of the circuit at this current maximum? Choose the correct answer below:

Answer:

i) OPEN Circuit ii) SHORT Circuit

f)

Why is the source current, *I*S, maximum at this frequency?

Answer:

** Plot 2 – Series Resonance Data**

**C. Construction of a Series or Parallel RLC Circuit and Measurement of Circuit Characteristics**

1. Construct the circuit in either Figure 3 or 4.

**Important note**: You **do not need** the **switch** arrangement for the parallel resonance circuit; The inductor self-resistance, which is an integral part, cannot be isolated as in the simulator analysis.

**Figure 3 – Parallel Resonance Circuit**

**Figure 4 – Series Resonance**

2. Set the function generator voltage to 10 V RMS. Use the same value for frequency as used in the simulator experiment.

3. Vary the source frequency as indicated in the simulation part of the lab exercise. Record the current readings. Tabulate the results below:

**Frequency, Hz**

*I***S**** (RMS), mA**

200

300

500

700

730

734

738

800

1000

1200

1400

**Table 3 – Circuit Measurement Results**

4. Are the simulated and calculated values the same?** ________** (**YES** or **NO**)

5. If you answered NO, explain why you think they differ.

**IV. TROUBLESHOOTING**