UNIVERSITY OF NEVADA LAS VEGAS. DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING LABORATORIES.

Class: EE221 Circuits II – 1001 Semester: Fall 2015

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Document topic: Postlab 5

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1. Introduction / Theory of OperationLab focused on the step response of RC, RL and RLC circuits. Step responses were recreated byintroducing a voltage source suddenly to a circuit. By using a pulse function we create a suddenintroduction of voltage to the circuits that is repeated, making us able to display the response onan oscilloscope in the form of a wave. The RC and LC circuits focused on the time constant,which indicates how fast a circuit charges / discharges. The focus on RLC circuits is damping ofvoltage/current due to the components. In both parallel and series RLC circuits there is arelationship to the resistor's value and whether the circuit is overdamped, critically damped, orunderdamped.

2. Description of ExperimentsExperiment 1:

Here we can see the rising curve that was predicted in the prelab.

We can see that at 5 time constants, that voltage across the resistor reaches approximately 0.993of it's full potential which is 5V * 0.993 = 4.965V. Experiment 2:

We notice with experiment 2 that the signal looks the same as the one in experiment 1. This isdue to the fact that we are sending multiple pulses, so there is a discharge period on top of thecharge period. The discharging part of the wave looks like the charging part of the wave inexperiment one.

Experiment 3:

Using equations and . We find that for a 4mH inductor and a 22nF capacitor

to cause a critically damped case we need a resistor of about 56ohm. Overdamped andunderdamped cases were demostrated using 10ohm resistor and a 10kohm resistor.

3. Encountered ProblemsThe three labs are simple theoretically, but that is not the case for one of them practically. Theone experiment that ended up giving us trouble is experiment 3. We were simply not getting theresults that were expected from the experiment. The equipment used in the lab was not suitablefor the values that were given from the lab. Instead of wasting more time the best alternative offinding more reasonable values of inductor and capacitor was taken. These values were selectedto be 4mH and 22nF.

4. SummaryIn experiment 1 we proved that for an RC circuit. We observed thatapplying a sudden voltage, or pulse, produced a rising voltage up to the maximum voltage as thecapacitor charged to full capacity over it's time constants. Likewise in experiment 2 we provedthat . As voltages pulsed up to maximum, the inductor apposed the voltagedifference until it allowed all the current to go through it, resulting in a decreasing voltage curveover time constants. The third experiment showed us that three different cases exists for RLCcircuits and specific component values cause each case.

5. ConclusionsThe first two labs really showed the fundamental properties of the capacitor and inductor. Thatthe capacitor does not allow for instant voltage difference across it when a pulse is applied to itin a RC circuit. Likewise in a LC circuit the inductor does not allow for a sudden change ofcurrent through it. The third experiment showed a little bit more than just circuit theory, itshowed us the reality sometimes cannot be predicted by theory. For instants in this lab wecalculated the theoretical value of resistances that causes the RLC circuit to be critically damped,but actually applying that resistance did not produce the expected results. This is because manyfactors, such as the allowable variance in the components expected value, as well as howtemperatures in the room affecting the values of resistance.