June 14, 2015
June 14, 2015
June 17, 2015
Electrical and Computer
26.136.1 - 26.136.9
A “Trick and Think” Approach to a Second-Order Circuit LabAs instructors, we always look to engage students in a way that keeps them alert, stimulates theirattention and interest, and adds some elements or insights to their skills. This is important in afirst circuit lab course, where students are struggling with many obstacles, such as understandingand performing correct circuit analysis, building the circuit on a breadboard, simulating it withappropriate software, and measuring relevant circuit parameters.One demanding task in a first circuit analysis lab course is the study of second-order circuits.The analysis of an RLC circuit, involving second order differential equations and differentregimes with underdamped or overdamped solutions is very demanding to sophomores, and thesubtleties of understanding and then designing circuit performances as needed by tuning valuesof the different components in the circuit might be lost or overlooked.In this paper I present one way to make a second-order circuit lab more lively, interesting andstimulating. In what might be called a “trick and think” approach, the students are provided witha prelab task to theoretically calculate and simulate the behavior of an RLC circuit with mixedserial and parallel features. The original circuit drawing provided to the student includes avoltage source that triggers the switch from one level of DC voltage to another, and the transientbehavior of the system is investigated.Students come to the lab after having solved and simulated the circuit, expecting to measure theunderdamped response that they obtained in their prelab solutions and simulations. To theirsurprise, the measurements show instead a clearly overdamped response.At this point the instructor opens a discussion inviting a brainstorming session on what could bethe cause of this inconsistency between theoretical/simulated values and measured ones. Ideasproposed by students are always interesting to hear; in some cases one of the students eventuallyoffers the correct explanation and suggestion; in many other instances the instructor has toproceed to one additional step and suggests running simulations with slightly altered values ofthe circuit parameters.Eventually, the mystery is solved and the solution pops out in a “Eureka” moment to one or moregroups. The original drawing lacks one additional resistance in the serial branch of the circuit,representing the internal resistance of the source! Once the students insert that resistance intotheir simulation, the response of the circuit flips from underdamped to overdamped. Of coursethe parameters of the original circuits have been chosen to be close to the critical dampingtransition, and insertion of the overlooked small internal resistance of the source tilts thebehavior of the response. Students are usually very elated at the moment “the puzzle” is solved.In this paper, I will show the different variants of the circuit and the corresponding simulations; Iwill also describe stimulating ideas and comments from students who undertook this lab exerciseover the many years it has been offered.
Gravé, I., & Estrada, T. (2015, June), A “Trick and Think” Approach to a Second-order Circuit Lab Paper presented at 2015 ASEE Annual Conference & Exposition, Seattle, Washington. 10.18260/p.23357
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