EMT1150_Lab3 - Resistors and Multimeter measurements(1)

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Mechanical Engineering

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Jan 9, 2024

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EMT1150 Lab Manual (08/2020) 1 | P a g e EMT1150 Lab Experiment 3 Resistors and Multimeter measurements Objective: To determine the Nominal (marked) value of the resistor by using the Color Code system. Use a Multimeter to measure the resistance value within a circuit. 3.1 Resistors and Color Coding 3.1.1 Resistance Resistors are electronic components that introduce a specific amount of resistance into electric circuits. If you went to the store to buy a resistor you would have to know the required power rating, the required resistance value, the tolerance you can allow, and the material that the resistor should be made of. The power rating of a resistor is an indication of how hot the resistor can get before burning up. Power rating is expressed in watts. Some common power ratings range from 200W down to 1/8 W. Usually, the power rating of a resistor is directly proportional to the physical size of the resistor: the higher the power rating, the bigger the physical size of the resistor. Carbon composition resistors are very popular. These resistors come in power ratings of 2W, 1W, 1/2W, 1/4W and 1/8W. The 2W resistor is as thick as a pencil while the 1/8W resistor is the size of a grain of rice. Table 3.1 shows the different size of resistors and its respective power rating. The resistor is usually identified by the letter R and either another letter or a number. Its resistance value is written next to it. The unit for the resistance value is the ohm , which is represented by upper case Greek omega ( ). It is customary to use the omega next to resistor values smaller than 1,000 ohms. Resistor values in the 1,000-ohm range or bigger are usually shown without the ohm symbol. Examples: 10 , 330 , 1.2 k , 1 M . Resistors and Power Rating 1/8 W resistor ¼ W resistor ½ W resistor 1 W resistor 2 W resistor 5 W resistor Table 3.1 – Resistors with difference power rating
EMT1150 Lab Manual (08/2020) 2 | P a g e 3.1.2 Resistor Color Code The value of the resistor in ohms and its tolerance are usually indicated by several bands of color grouped together on the left side of the resistor body. Most resistor has 4 bands together, the first and second band indicate the first two significant figures of the resistor value, the third band indicates the multiplier and the fourth band indicates the tolerance. Usually, the first three bands are close together and the fourth band is a little bit apart. Figure 3.1 Resistor with four color bands Resistors that have more than four colors, the other colors usually indicate the reliability (failure rate) of the resistor in % over 1000 hours of operation. It means how many resistors out of 100 will change their values to fall outside the allowed tolerance range after 1000 hours of operation. Also, some resistors with five colors means that the three first colors are the three resistance digit respectively, the forth color is the multiplier, and the fifth band is the tolerance. In order to indicate resistor values, manufacturers agreed to use the following value for each color: Value Color Tolerance Color 0 Black 20% No color 1 Brown 10% Silver 2 Red 5% Gold 3 Orange 4% Yellow 4 Yellow 3% Orange 5 Green 2% Red 6 Blue 1% Brown 7 Violet 0.5% Green 8 Gray 0.25% Blue 9 White 0.1% Violet 0.1 Gold 0.005% Gray 0.01 Silver Table 3.2 Color code for resistance value Table 3.3 Color code for tolerance Example 3.1 – Finding the resistance value using color coding For the following resistor, read the resistance value of the following resistor and find the lowest and highest resistance value 4th band 1st band 2nd band 3rd band
EMT1150 Lab Manual (08/2020) 3 | P a g e Solution: Identify the order of the color band and read the equivalent value for each color: - 1 st band = Blue = 6 - 2 nd band = Gray = 8 - 3 rd band = Red = 2 - 4 th band = Gold = + 5% Combining all digits together, we have 6 8 × 10 2 + 5% Ω Converting the value in engineering notation, we have 6 . 8 × 10 2+1 = 6. 8 × 10 3 6.8 k + 5% (Actual resistance value) To find the lowest and the highest resistance, we find the tolerance resistance first: 𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇 𝑇𝑇𝑇𝑇𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇 = 5% 𝑇𝑇𝑜𝑜 6.8 𝑘𝑘Ω = 5 100 × 6.8 𝑘𝑘Ω = 𝟎𝟎 . 𝟑𝟑𝟑𝟑 𝒌𝒌𝛀𝛀 Lowest resistance = actual resistance – tolerance resistance = 6.8 kΩ 0.34 kΩ = 6.46 kΩ Highest resistance = actual resistance + tolerance resistance = 6.8 kΩ + 0.34 kΩ = 7.14 kΩ 3.2 Multimeter Digital Multimeter (DMM) are the most common piece of electrical test equipment. They have the ability to measure voltage, current, resistance, and often many other function such as checking the reverse biasing of a diode. Understand the multimeter parts Multimeter typically has a set of terminal sockets marked as VΩ, A, COM, and a function selector switch, measure dial, or set of push buttons to select ranges and measurement functions as shown in Figures. Terminal socket VΩ stands for Volts and Ohms, which are the electrical unit of voltage and resistance, respectively. This terminal is used to measure voltage and resistance. Terminal A stands for Ampere, which is the unit for electric current. This terminal is used to measure current. Some multimeters have mAVΩ in one socket and some others have them separated as VΩ and A. The terminal COM stands for common terminal and it is the common terminal for all measurements.
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