Ac Circuits Lab Report

Objectives:

Alternating current supplies may be obtained for electromagnetical generators or from oscillators or signal generators. All AC waveforms are either sinusoidal or combinations of sinusoidal waves.

The objectives of this experiment are to determine the RMS value of an Ac voltage, the average value of an AC voltage and to measure phase displacement.

Equipment list:

1. 600mH Inductor

2. Oscilloscope with x1 Probe

3. 120/25V Multi-tap Transformer

4. Digital Multimeter

5. Identical 32V 30W lamps on a lamp board

6. Dual D.C. Power supply (output > = 5000mA)

7. Protoboard and component kit

8. Decade resistor box

9. 1AMP diode (1N4001 or !n4004)

Procedures:

PART I - THE EFFECTIVE VALUE OF A.C.VOLTAGE

l. We connect the apparatus as shown in Figure 1 and adjust the D.C. power until the A.C. powered lamp has the same brightness as the D.C. lamp.

2. Using the oscilloscope (with channel coupling selector set to D.C.), we measure the D.C. voltage applied to lamp LZ.

3. Now we measure the peak value of voltage applied to lamp L, (leave the channel coupling selector set to DC).

4. We modify the AC lamp connection as shown in Figure 2 (double power to L1) and adjust the D.C. power until the A.C. powered lamp has the same brightness as the D.C. lamp.

5. Following the procedure (steps 2 and 3) and use the oscilloscope to measure the A.C. and D.C. voltages carefully.

PART II - AVERAGE VALUE OF A.C. VOLTAGE

1. We connect the apparatus as shown in Figure 3, without making the connection between the diode and the transformer yet.

2. Connect the diode to the 12.SVolt tap on the transformer and plug the transformer in. We measure the peak voltage of the waveform with the oscilloscope and record this value below. Measure the DC voltage with the Multimeter and record this value below.

3. Unplug the transformer and connect the diode to the 25.OVolt tap and once again measure and record the peak voltage and the dc voltage as before. The values are recorded on the Lab Report Sheet.

PART III - PHASE ANGLE MEASUREMENT

The resistor voltage varies directly with the current and is used to represent the current

VR = R x i

1. We set the Time/cm switch to "x via YA" and set both voltage selectors to 10V/cm.

The supply voltage sample is applied to YA and the current sample is fed to YB, and the ellipse displayed on the screen will enable you to calculate the "Phase angle between the supply voltage and the resulting current".

2. We set the Time/cm switch to an appropriate time setting to see the two waveforms. When these are steady, sketch the waveforms on the Lab Report Sheet.

The horizontal distance between consecutive pairs of positive going zero crossings on one wave may be interpreted as the period (T) of the wave, or as 360 electrical degrees. The time base can be expanded so that each centimeter represents say 45 or 60 degrees. The angle of phase difference between the voltage wave and the current wave may then be more easily estimated. See Figure 6.