LAB INTRO OHM's LAW

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School

Lawrence Technological University *

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Course

4214

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Electrical Engineering

Date

Dec 6, 2023

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docx

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Uploaded by BrigadierClover826

1 Ohm’s Law NAME:________________________ Prof. K. Cook General Information It is important to come prepared to lab. This includes the class text, the lab exercise for that day, class notebook, calculator, and hand tools. The tools include an electronic breadboard, test leads, wire strippers, and needle nose pliers. and your own DMM (digital multimeter). A typical breadboard or protoboard is shown below: This particular unit features two main wiring sections with a common strip section down the center. Boards can be larger or smaller than this and may or may not have the mounting plate as shown. The connections are spaced 0.1 inch apart which is the standard spacing for many semiconductor chips. These are clustered in groups of five common terminals to allow multiple connections. The exception is the common strip which may have dozens of connection points. These are called buses and are designed for power and ground connections. Interconnections are normally made using small diameter solid hookup wire, usually AWG 22 or 24. Larger gauges may damage the board while smaller gauges do not always make good connections and are easy to break. The color highlighted sections indicate common connection points. Note the long blue section which is a bus. This unit has four discrete buses available. When building circuits on a breadboard, it is important to keep the interconnecting wires short and the layout as neat as possible. This will aid both circuit functioning and ease of troubleshooting. LAB REPORTS Lab exercises require a non-formal laboratory report. Lab reports are individual endeavors not group work. The deadline for reports is one week after the exercise is performed . A letter grade is subtracted for the first week late and two letter grades are subtracted for the second week late . Reports are not acceptable beyond two weeks late . The report should include a statement of the Objective (i.e., those items under investigation), a Conclusion (what was found or verified), a Discussion (an explanation and analysis of the lab data which links the Objective to the Conclusion), Data Tables and Graphs and Photo’s if applicable, and answers to any problems or questions posed in the exercise.

2 ENGINEERING NOTATION Scientists and engineers often work with very large and very small numbers. The practice of using commas and leading zeroes proves to be cumbersome. Scientific notation is more compact and a less error prone method of representation. Numbers is split into two portions: a precision part (the mantissa) and a magnitude part (the exponent, being a power of ten). For example, the value 23,000 could be written as 23 times 10 to the 3 rd power. The exponent may be thought of in terms of how many places the decimal point is moved to the left. Spelling this out is awkward. Therefore, a shorthand method is used where “times 10 to the X power” is replaced by the letter E (which stands for exponent). Thus, 23,000 could be written as 23E3. The value 45,000,000,000 would be written as 45E9. Note that it would also be possible to write this number as 4.5E10 or even .45E11. The only difference between scientific notation and engineering notation is that for engineering notation the exponent is always a multiple of three . Thus, 45E9 is proper engineering notation but 4.5E10 isn’t. On most scientific calculators E is represented by either an “EE” or “EXP” button. The process of entering the value 45E9 would be depressing the keys 4 5 EE 9. For fractional values, the exponent is negative and may be thought of in terms how many places the decimal point must be moved to the right. Thus, .00067 may be written as .67E-3 or 6.7E-4 or even 670E-6. Note that only the first and last of these three are acceptable as engineering notation. Engineering notation goes one step further by using a set of prefixes to replace the multiples of three for the exponent. The prefixes are: E12 = Tera (T) E9 = Giga (G) E6 = Mega (M) E3 = kilo (k) E-3 = milli (m) E-6 = micro (µ) E-9 = nano (n) E-12 = pico (p) Thus, 23,000 volts could be written as 23E3 volts or simply 23 kilovolts.

3 DC SOURCES & METERING The adjustable DC power supply is a mainstay of the electrical and electronics laboratory. It is indispensable in the prototyping of electronic circuits and extremely useful when examining the operation of DC systems. Of equal importance is the handheld digital multimeter or DMM. This device is designed to measure voltage, current, and resistance at a minimum, although some units may offer the ability to measure other parameters such as capacitance or transistor beta. Along with general familiarity of the operation of these devices, it is very important to keep in mind that no measurement device is perfect; their relative accuracy , precision , and resolution must be considered. Accuracy refers to how far a measurement is from that parameter’s true value. Precision refers to the repeatability of the measurement, that is, the sort of variance (if any) that occurs when a parameter is measured several times. For a measurement to be valid, it must be both accurate and repeatable. Related to these characteristics is resolution . Resolution refers to the smallest change in measurement that may be discerned. For digital measurement devices this is ultimately limited by the number of significant digits available to display. A typical DMM offers 3 ½ digits of resolution, the half-digit referring to a leading digit that is limited to zero or one. This is also known as a “2000 count display”, meaning that it can show a minimum of 0000 and a maximum of 1999. The decimal point is “floating” in that it could appear anywhere in the sequence. Thus, these 2000 counts could range from 0.000 volts up to 1.999 volts, or 00.00 volts to 19.99 volts, or 000.0 volts to 199.9 volts, and so forth. With this sort of limitation in mind, it is very important to set the DMM to the lowest range that won’t produce an overload in order to achieve the greatest accuracy. A typical accuracy specification would be 1% of full scale plus two counts. “Full scale” refers to the selected range. If the 2 volt range was selected (0.000 to 1.999 for a 3 ½ digit meter), 1% would be approximately 20 millivolts (0.02 volts). To this a further uncertainty of two counts (i.e., the finest digit) must be included. In this example, the finest digit is a millivolt (0.001 volts) so this adds another 2 millivolts for a total of 22 millivolts of potential inaccuracy. In other words, the value displayed by the meter could be as much as 22 millivolts higher or lower than the true value. For the 20 volt range the inaccuracy would be computed in like manner for a total of 220 millivolts. Obviously, if a signal in the vicinity of, say, 1.3 volts was to be measured, greater accuracy will be obtained on the 2 volt scale than on either the 20 or 200 volt scales. In contrast, the 200 millivolt scale would produce an overload situation and cannot be used. Overloads are often indicated by either a flashing display or a readout of “OL or E”. RESISTOR COLOR CODE The resistor is the most fundamental of all electrical devices. Its attribute is the restriction of electrical current flow: The greater the resistance, the greater the restriction of current. Resistance is measured in Ohms . The measurement of resistance in unpowered circuits may be performed with a digital multimeter (DMM). Like all components, resistors cannot be manufactured to perfection. There will always be some variance of the true value of the component when compared to its nameplate or nominal value. For precision resistors, typically 1% tolerance or better, the nominal value is usually printed directly on the component. Normally, general purpose components, i.e. those worse than 1%, usually use a color code to indicate their value. The resistor color code typically uses 4 color bands. The first two bands indicate the precision values (i.e. the mantissa) while the third band indicates the power of ten applied (i.e. the number of zeroes to add). The fourth band indicates the tolerance. It is possible to find resistors with five or six bands but they will not be examined here. Examples are shown below:

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