OHM’S LAW LAB



ELECTRONICS

NAME:

RLC LAB

OBJECTIVES

At the completion of this experiment, you will be able to:

--Understand series reactance and resistance.

--Determine the net reactance, phase angle, and the impedance of an RLC circuit.

INTRODUCTION

Both the previous experiments, RL series circuit, and RC series circuit, were AC circuits. In both cases, the concept of reactance was investigated. The results showed that the reactive component had its own voltage drop that was out of phase with the resistive component, although the circuit current was the same in all parts of the circuit.

In an RLC series circuit, the same concepts apply. However, when XL and XC are both in the circuit, the opposite phase angles enable one to cancel the effect of the difference between the two series reactance, resulting in less reactance than either one alone.

Consider the circuit of Fig 31-1. Notice that the circuit current is found by dividing the applied voltage by the total net reactance of the circuit. Here,

120v = 6A

20Ω

The net reactance is the difference between XL = 60Ω and XC = 40Ω. In the same manner, the difference between the two voltages is equal to the applied voltage, because the IXL and IXC voltages are opposite. If the values were reversed, the net reactance would be 20Ω -- XC. The current would still be 6A, but it would have (-900) phase angle instead of (+900).

When resistance is added to the circuit, the total effect is determined by phasors. The phasor for the circuit of Fig. 31-1, would be:

With a resistor added in series:

LAB PROCEEDURE

Components Needed:

1K( resistor

100mH inductor

.1 uF capacitor

Signal Generator

Proto-Board

(Resistor is ½ watt)

PROCEEDURE

1. Connect the circuit of Fig. 31.5

2. Using and oscilloscope, measure the voltage across the capacitor, Vc, the inductor, Vl, and the resistor, Vr. Record these values on the data sheet 31-1.

Note: Avoid ground loops when measuring voltage with the oscilloscope by moving the resistor and the inductor to keep the ground leads of the signal generator and the oscilloscope connected together.

3. Calculate and record the values of XL and XC in the data sheet 31-1.

4. Calculate and record the value of Z, impedance, for the circuit. Record in the data sheet 31-1.

5. Calculate the value of I, and record the results on the data sheet 31-1.

6. Calculate the values for VR, VL, and VC. Record the values in data sheet 31-1.

7. Calculate the phase angle for the circuit and record in the data table 31.1.

Using EXCEL, create a graph for XL and XC vs Frequency.

Your chart should look like this:

|F |Xl=6.28*F*L |Xc=1/(6.28*F*C) |

|200 |  |  |

|400 |  |  |

|600 |  |  |

|800 |  |  |

|1000 |  |  |

|1200 |  |  |

|1400 |  |  |

|1600 |  |  |

|1800 |  |  |

|2000 |  |  |

|2200 |  |  |

|2400 |  |  |

|2600 |  |  |

|2800 |  |  |

|3000 |  |  |

|3200 |  |  |

|3400 |  |  |

|3600 |  |  |

|3800 |  |  |

|4000 |  |  |

Indicate on your graph the point at which “Resonance” would occur.

DATA TABLE

Measured Calculated Calculated Calculated

VR _______ XL _______ VR _______ Phase Angle _______

VL _______ XC _______ VL _______

VC _______ Z _______ VC _______

I _______

-----------------------

Fig. 31-1 LC circuit reactance. Net reactance is equal to Xl – Xc. 60[?] gˆ‰îü 2 5 VWYZ`c?ž¤¥"

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hU3H5?\? hU3H5?Ω - 40Ω = 20Ω

XL=60Ω

XC=40Ω

XL= 20Ω

XL=60Ω

XC=40Ω

Net

XL=20Ω

XL=60Ω

XC=40Ω

R=100Ω

Net

XL=20Ω

R=100Ω

[pic]

Fig. 31.5

Data Sheet 31-1

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