EET-117_LAB 4_24W-REVISED_pdf

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Centennial College *

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Electrical Engineering

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Feb 20, 2024

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Centennial College ELECTRICAL ENGINEERING TECHNICIAN & TECHNOLOGY Course: EET-117 Name(s) Student Number(s) Date Lab #4 MEASUREMENT OF RESISTANCE Based on Experiments in Basic Circuits by David Buchla Objectives: 1 Determine the listed value of a resistor using the resistor colour code. 2. Use the DMM (or VOM) to measure the value of a resistor. 3. Determine the percent difference between the measured and listed values of a resistor. 4. Measure the resistance of a potentiometer and explain its operation. Required Instruments and Components: DMM (Digital Multi-meter) VOM Power supply Breadboard Alligator test leads (from the EET-117 labkit) Resistors: 5 assorted value resistors (from the EET-117 labkit) Potentiometer of any value (from the EET-117 labkit – example: when it is labelled “103” it is – 10x10 3 Ohm or 10 kOhm resistor) or Elenco XK-150 (1 kOhm or 100 kOhm)

Procedure 1. Orient the 5 resistors so that the colour bands may be properly read from left-to-right on the breadboard as is shown in Figure 1. Make sure to leave a 5-hole spacing between the resistors to facilitate individual measurements. Fig. 1 2. Determine the colour codes for the resistors and record them in Table 1. 3. Use the NULL function to correct the test lead’s resistance. Before taking any resistance measurements with the DMM, always make sure to check the meter's ZERO ERROR. Our DMM (Keithley 2110) has an auto-zero function that is automatically turned ON (p.81 of the manual). Over time and prolonged use, meters tend to go out of proper calibration and this will result in ZERO ERROR. In addition to the above, the test leads (their resistance) may impact the correctness of the readings. When the null feature is enabled, the displayed reading is the difference between the measured input signal and the stored null (also called relative) value: Displayed reading = Measured input reading - Null value You can acquire the null (relative) value by measurement or by specifying the value. The null value is stored in volatile memory, which will be cleared when power to the instrument is cycled. Cancel out test-lead resistance that can result in inaccurate low-level resistance Measurements. The subsequent resistance measurement reading will exclude the test lead resistance. a. Turn the DMM ON b. Press Ω2 to select the 2-wire ohm measurement. c. Connect the test leads to the instrument as shown below and connect them together (without a resistor). Fig. 2 d. Record the Resistance value shown on the display (test-lead resistance): _____________________ e. Use the NULL function to correct the test lead’s resistance. Fig. 3

4. With the Digital Multimeter (DMM) measure the actual ohmic value for each resistor and enter the results into Table #1. IMPORTANT: Make sure to wait for the meter's reading to stabilize before recording it into the table. 5. Use the % tolerance value to calculate the Minimum and Maximum possible resistance values for each resistor (Resistance Range) and determine (Yes or No) if the measured values fall within the tolerance range specified by the manufacturer. 6. Compute the percent difference between the measured and colour-coded values using the equation: Table 1. Experimental data readings (columns 2-5 and 9 to be completed in the lab). Are all the measured values for the resistors within the manufacturer's tolerance specifications? Indicate those that are out of tolerance. Marks: / 30 3 1 1 1 RESISTOR BEING TESTED BAND # 1 BAND # 2 BAND # 3 BAND # 4 Resistor value (Ω) Resistance range (calculated) DMM Measurement ( Ω ) % Dif. Is a tolerance within the range? (Y/N) Mark 1ST DIGIT 2ND DIGIT x10n Multiplier ±% Tolerance Min (Ω) Max ( Ω ) 1 2 3 4 5 6 7 8 9 10 11 EXAMPLE Colour orange orange orange gold 33000 33000- 1650= 31350 33000+ 1650= 34650 32500 -1.5% Y - Code # 3 3 3 ± 5% 1 Colour /6 Code # 2 Colour /6 Code # 3 Colour /6 Code # 4 Colour /6 Code # 5 Colour /6 Code #

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7. Remove all resistors from the breadboard but set aside two resistors with the largest and the smallest value for the next measurements. 8. Re-measure the values of the two resistors, but don't place them in the breadboard for measuring, instead hold the resistor leads and the meter probes between your fingers as shown in Figure 4. Record the readings in Table 2. Fig. 4 ( NOTE : This is an INCORRECT way of measuring resistance) Table 2 (all columns to be completed in the lab). Measured value as per Fig. 4 Measured value as per Table 1 Do you observe any difference between the two measurements? Explain below Marks: / 10

9. Use any potentiometer from your labkit. Number the terminals 1, 2, and 3, as illustrated in Fig. 5. Vary the potentiometer's shaft while you monitor the resistance between terminals 1 and 3. Notice that the resistance between the outside terminals does not change as the shaft is varied. Record the resistance between terminals 1 and 3 of the potentiometer (the outside terminals) in Table 3. Fig. 5 10. Turn the potentiometer completely counterclockwise (CCW – these potentiometers have an adjustment of 280 degrees nominal). Measure the resistance between terminals 1 and 2. Then measure the resistance between terminals 2 and 3. Record the measured resistances in Table 3. Compute the sum of the two readings and record it in Table 3. 11. Turn the shaft 90 degrees clockwise (CW) and repeat the measurements in step 10. 12. Turn the shaft another 90 degrees (180 degrees total) in the same direction (CW) from the starting point and repeat the measurements in step 10. Table 3 Marks Step 9: Total resistance between terminals 1 and 3: /1 Step Shaft Position Resistance Measured Between: The sum of Resistance Readings Terminals 1- 2 Terminals 2 -3 10 O degrees (fully CCW) /3 11 90 degrees CW /3 12 180 degrees CW /3 Marks: / 10

REVIEW QUESTIONS 1. D e termine the resistor colour code for the following resistors. The tolerance is 10%. Value 1 st band colour 2 nd band colour 3 rd band colour 4 th band colour Mark 1 k Ω / 2 22 0 Ω /2 3.3 kΩ /2 10 k Ω / 2 1 M Ω /2 Marks: / 10 2. Determine the expected value for resistors with the following colour codes. 1 st band colour 2 nd band colour 3 rd band colour 4 th band colour Value Mark green red red gold / 2 v iolet green brown silver /2 gr e en brown orange gold /2 whi t e red gold gold /2 grey red yellow s ilver /2 Marks: / 10 3. A resistor is colour - coded red - black-red-silver . N Question Answer Mark Q1 What is the resistance value of the resistor? /2 Q2 What is the largest value the resistor can be and still be in tolerance? / 2 Q3 What is the smallest value the resistor can be and still be in tolerance? /2 Marks: / 6 4. This experiment described how to read 5% and 10% tolerance resistors. The same idea is used for most 1% and 2% resistors except that 1% and 2% will have one more colour band than 5% and 10% resistors. The first three bands represent the first, second, and third significant figures. The fourth band represents the multiplier band. The decimal point is assumed to be after the third significant figure and then moved by the amount shown in the multiplier band. The fifth band represents the tolerance band. A 1% resistor has a brown tolerance band and a 2% resistor has a red tolerance band. There is a space between the fourth and fifth bands to avoid mistaking the tolerance band for the first significant figure and mistakenly reading the resistor backward. For each of the resistors shown in Table 4, find the remaining information and complete the table. The first line is completed as an example.

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Table 4 Resistor Colour of Band Colour-code value Minimum value Maximum value Mark 1 st 2 nd 3 rd 4 th 5 th 0 brown red violet brown gold 1.27 kΩ ± 5 % 1.24 kΩ 1.30 kΩ 1 356 Ω ± 1 % /4 2 5.38 MΩ ± 2 % /4 3 128 kΩ ± 1 % /4 4 orange green black gold red /4 5 brown violet black black brown /4 Marks: /20 5. What is the consequence of using a resistor with a wattage rating lower than the circuit requires? __________(2 marks) A) The resistor may overheat and potentially fail B) The resistance will double C) The circuit will become more energy-efficient D) The resistor will become a conductor 6. What is the primary function of a potentiometer in a circuit? __________(2 marks) A) To store electrical energy B) To store chemical energy C) To measure the current D) To regulate the resistance Conclusions. The conclusion summarizes the important points of the laboratory work. You must analyze the examples to add emphasis to significant points. You must also include features and/or things you have done /benefits of a particular procedure, instrument, component, or circuit directly related to the experiment . Marks: / 2 0

Rubric-Grading Criteria Max. Marks Punctuality 10 Lab Safety 20 Procedure 50 Review Questions 50 Conclusion 20 Neatness, Spelling, Grammar, and Sentence Structure 10 Total: /160