basic electercity

Name:		Lab:	6
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Lab 6: AC Waveforms and Characteristics

Objective:

After completing this exercise, you should be able to:

· Identify the primary functions and controls on a two channel oscilloscope

· Calculate RMS Voltage and Current for Single element resistive circuits

· Apply Kirchhoff’s Voltage Law to series AC resistive circuits

· Use the oscilloscope to measure the voltage across elements within an AC circuit.

Materials:

1 x	Elvis Unit with: Variable Power Supply Prototyping board	1 x	Digital Multi-Meter Fluke 179 or equivalent
1 x	2 channel Oscilloscope Tektronix TDS210 or DPO2012 or equivalent	2 x	2 kΩ
		1 x	1 kΩ, 3.3 kΩ

Discussion:

Our investigation into electricity to this point has focused on DC sources and circuits. This has provided us with the opportunity to investigate the fundamental laws of electricity with a constant source. Many applications however use AC or Alternating Current to supply power or information to a circuit. For this reason, it is imperative that an understanding of AC waveforms and characteristics is developed.

This Lab will provide an introduction to alternating current. It will provide an introduction to the use of the oscilloscope and the function generator. Both these instruments are fundamental in the design and analysis of advanced electrical circuits.

Procedure:

1.

Determine Vpk, Vp-p, VRMS, T, and f of the signal illustrated to the right and record the results in the table below.

Vpk =
Vp-p =
VRMS =
f =
T =

2. Construct the circuit shown in the circuit diagram to the right. Use the function generator on board the ELVIS unit as your signal source and an oscilloscope to verify the voltage and period of the signal measured across the resistor R1. Record the measured values for Vpk and T in the table below. Refer to the explanation below to setup the function generator on the Elvis Unit.

Vpk =
T =

Refer to the diagram to the right for proper configuration of the Function Generator on board the Elvis unit.

a.

Launch the Elvis Instrument Launcher under the National Instruments/NI Elvismx Directory

b. Select the Function generator by clicking on FGEN.

c. Set the Frequency to 25 kHz.

d. Set the Amplitude to 8 Vpp.

e. Select “Prototype board” for Signal Route. This will provide the output of the function generator to pin 33 of the lower left distribution point. Make sure you use the ground reference on either pin 49 or 54 as your circuit ground.

f. Click “Run” to activate the function generator output.

3. Calculate the RMS Voltage and current for the circuit in step 2. Use these values to determine the power dissipated by R1.

4. Use a DMM to measure the RMS current and voltage in the circuit above. Record the results from steps 3 and 4 in the table below.

	VRMS	IRMS	PR1
Calculated
Measured

5. Repeat step 4 with f = 500 hz. Record the measured RMS current and Voltage in the table below.

	VRMS	IRMS
Measured

6.

Construct the circuit shown in figure 3. Determine RT, VRMS, and IRMS and PAve for the circuit. Record these results in Table 4

Table 4
RT =
VRMS =
IRMS =
PAve =

7. Use the Oscilloscope to measure Vpk at

,

image4.png

, and

image6.png

. Recall from earlier discussions that

image8.png

. Use this approach to determine

image10.png

and

image12.png

. Record these results in the table below.

image13.png	image14.png	image15.png	image16.png	image17.png

Questions:

1. How does the Power calculated in step 3 compare to the peak power of the circuit in step 2?

2. Explain the differences between the RMS measurements in steps 4 and 5 above. Refer to the Fluke 179 User Manual for reference.

3. What quantities do

and

image21.png

represent? Why can these quantities not be determined directly?

Simulation Exercise:

1. Use MultiSim to construct the circuit to the right. Note: You do not need to include the nodes

Va and Vb.

2. Determine the total resistance of the circuit. Record this value below.

RT =

3. Use the Virtual Oscilloscope within Multisim to measure the voltage at Va and Vb.

4. Calculate

and the total circuit current. Record the results from steps 3 and 4 in the table below.

image24.png	image25.png	image26.png	IPk

Questions:

1. What was the effect of R3 on the circuit?

2. Is there a relationship between VR3 and the circuit current? What is it?

3. Can an oscilloscope be used to directly measure current? Indirectly?