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Polytechnic of namibia http

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Evandro Conceicao

This lab report summarizes two experiments measuring resistance and voltage. In the first experiment, the resistance of three resistors was calculated from their color codes and measured with a digital multimeter. The measured values were within 5% of the calculated values, validating the accuracy of using color codes. In the second experiment, the voltage output of a power supply was measured at increasing levels and found to be slightly lower than the power supply readings due to internal resistance dropping voltage. The experiments helped familiarize the student with lab equipment and electrical measurements.

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1 Introduction Electricity is an essential part of the modern life experience, and as an engineer it is essential to know how it behaves and responds to changes in its trajectory. This lab was divided into two parts namely Part 1 is about measuring resistance using the colour coding technics and proving it with the (Digita l Multimeter) hence forth referred to as (DMM) and part 2 is working with the power supply and the(DMM) to determine voltage. The main goal of the lab is to get used to carbon resistors and determining their values from specification (colour codes) and measurements. And to show that the colour code method of identifying resistance tolerance through its colour coding is relativel y accurate. The purpose is to get familiarized with lab equipment, analyse simple resistors, measure circuit properties such as voltage and resistance through two conductors. Theory Basic definitions needed for the complete understanding of the content of this report: Voltage is electrical potential energy per unit charge which is measured in joules per coulomb which has its SI unit as volts. Resistance is defined as the opposition within a conductor to the passage of electric current which has its SI unit as Ohms (立). Carbon resistor are the components which are placed in a circuit to oppose current flow. Power supply is a device that supplies electric power to an electrical load. Basic formulas & other relevant information 躯″ ｍ ｍ 躯″ ｍ 100 ( ) Tolerance Colour Codes No Band = 20%; Silver = 10 %; Gold = 5% and Red=2%.
2 Pre-Lab Question 1: a) R= (Brown, Black)10red R= 10102= 1000立 Tolerance= Silver= 10% 10 100 1000 = 100立 Therefore this resistor has a value tolerance between 900立 and1100立 b) R= (Red, Green, Black) 10brown R= 250101= 2500立 Tolerance= Red = 2% 12 100 2500 = 50立 Therefore this resistor has a value tolerance between 2450立 and 2550立 b) R= (Brown, Black)*10blue R= 10106=10M立 Tolerance= Gold= 5% 5 100 10000000 = 500000 立 =0.5 M立 Therefore this resistor has a value between 9.5M立 and 10.5M立 Question 2: a) 1.75 k立 賊2% 1.751000= 1750 立 According to the Colour codes 1=brown, 7= violet, 5=green, brown= 2 and red is 2% The colour code is {Brown, Violet, Green, Brown, and Red} b) 10M立 賊5% 10106= 10000000 立 According to the colour codes 1= brown, 0= black, 6= blue and gold is 5% The colour code is {Brown, Black, Blue, and Gold}
3 c) 38k立 賊5% 381000= 38000 According to the Colour codes 3= orange, 8= grey, 3= orange and gold is 5% The Colour code is {Orange, Grey, Orange, and Gold} Equipment used Power supply Digital Multimeter (DMM) which serves as a Voltmeter and Ammeter Three carbon resistors with different resistances Two conductors Procedures To Measure Voltage: Change the voltage selection knob on the DMM to (DC or V) for DC measurement. Voltage is measured in parallel with the load and the range of your measurement can be altered by using the Range buttons. To Measure Current: Change the current outlet of the DMM to (+ terminal) and the COM outlet (ground). Current is measured in series you will have to break the circuit to measure current. For a current less than 200mA use the outlet (V立A) and for current greater than 200mA use the outlet written 20A in red else the DMM will not be accurate and may not show the current reading. You can vary the range of your measurement by using the Range buttons. To Measure Power Supply Voltage: A voltmeter is always connected in parallel across your load or power supply. The + terminal of the voltmeter should be connected to the + terminal of the Power Supply hence forth referred to as (PS) (usually the red outlet) and the - terminal of the voltmeter to the - terminal of the PS (usually the COM or black outlet) of the DMM. Part 1 of the lab 1. Push the power button to turn on the multi-meter. 2. To use the DMM as an ohmmeter, turn the knob so that it points on the side of resistance, where there is (立) symbol. 3. Get three resistors from your toolbox.
4 4. From the colour code of each resistor, determine the resistance and the tolerance of each resistor. 5. Calculate the range of resistance values for each resistor based on the tolerance of the resistors. 6. These results were recorded on the table provided. 7. Using the DMM, measure the resistance of each resistor. 8. To do this try to seek advice from the laboratory assistant (insert a red banana-to-clip connector into the 立-plug and a black banana clip connector into the COM-plug). Place the resistor-under-test between the red and the black connectors. 9. Record this on the table provided. Part 2 of the lab 1. Set the Meter knob of the PS to the +5 V position, and connect the two wires from the PS (+ V and COM outlets) to the voltmeter. 2. Since youre measuring DC voltage, press the --V button and maximum range on your Multimeter. 3. Adjust the output of the PS by using the Voltage +5 V knob. 4. Check your voltage by reading the volts scale of your PS (lower reading) and compare it to the voltmeter reading. Results Part 1 results: Measuring Resistance Exercise Calculations using Equation (1) % Error R1= 560 570 560 100 = -1.79% R2= 2727.2 27 100 = -0.74% R3= 4746 .9 47 100 = 0.2% Table 1 Resistor Colour Codes Value of resistance calculated from colour code Measured value or resistance % Error R1 Green, Blue, Brown, Gold 560立 賊5% 570立 -1.79% R2 Red, Violet, Black, Gold 27立 賊5% 27.2立 -0.74% R3 Yellow, Violet, Black, Gold 47立 賊5% 46.9立 0.2%
5 Table 2 Part 2: Use of Power Supply Exercise Readings from Power Supply and Voltmeter respectively Power Supply Voltmeter 5V 5.05V 10V 9.96V 15V 15.03V 20V 19.9V 25V 24.9V 30V 29.8V Table 3 Discussions Part 1: Tolerance for all the resistors is more or less 5%. The negative percentages just mean that the amount that we have calculated has been exceeded by that percentage, and the positive percentages just mean that the amount that we have calculated has not been exceeded by that percentage. All the errors for each resistance measured fall within the calculated ranges. Therefore the method of calculat ing resistance ranges using colour codes is approximately accurate and can be used as an alternative to measuring the resistances all the time. Part 2: The reason why the voltmeter readings are slightly lower or bigger is because the power supply has an internal resistance. Within the conductors energy is converted into other forms of energy such as (heat) causing the voltage drop. This affects the potential difference as proven above with table number 3. Conclusion: In conclusion I have learned how to operate the DMM and that making the use of colour codes to calculate the resistance of a resistor is faster than actually measuring that resistance. The errors due to these calculations is very small and is within the range of resistivity of the resistor. There is also the matter of the conversion of electricity from one form to another that I have noticed while doing the last exercise in which the voltage readings are quite different from the real ones. This is due to
6 the elements that contribute to the resistance namely (length of conductor, material of conductor, cross sectional area of the conductor and the material from which the conductor is made from). Furthermore I think that these findings were useful in the sense that I now understand more about electrical circuits than before these lab and that it will contribute to the foundation of my engineer ing career.

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Polytechnic of namibia http

  • 1. 1 Introduction Electricity is an essential part of the modern life experience, and as an engineer it is essential to know how it behaves and responds to changes in its trajectory. This lab was divided into two parts namely Part 1 is about measuring resistance using the colour coding technics and proving it with the (Digita l Multimeter) hence forth referred to as (DMM) and part 2 is working with the power supply and the(DMM) to determine voltage. The main goal of the lab is to get used to carbon resistors and determining their values from specification (colour codes) and measurements. And to show that the colour code method of identifying resistance tolerance through its colour coding is relativel y accurate. The purpose is to get familiarized with lab equipment, analyse simple resistors, measure circuit properties such as voltage and resistance through two conductors. Theory Basic definitions needed for the complete understanding of the content of this report: Voltage is electrical potential energy per unit charge which is measured in joules per coulomb which has its SI unit as volts. Resistance is defined as the opposition within a conductor to the passage of electric current which has its SI unit as Ohms (立). Carbon resistor are the components which are placed in a circuit to oppose current flow. Power supply is a device that supplies electric power to an electrical load. Basic formulas & other relevant information 躯″ ｍ ｍ 躯″ ｍ 100 ( ) Tolerance Colour Codes No Band = 20%; Silver = 10 %; Gold = 5% and Red=2%.
  • 2. 2 Pre-Lab Question 1: a) R= (Brown, Black)10red R= 10102= 1000立 Tolerance= Silver= 10% 10 100 1000 = 100立 Therefore this resistor has a value tolerance between 900立 and1100立 b) R= (Red, Green, Black) 10brown R= 250101= 2500立 Tolerance= Red = 2% 12 100 2500 = 50立 Therefore this resistor has a value tolerance between 2450立 and 2550立 b) R= (Brown, Black)*10blue R= 10106=10M立 Tolerance= Gold= 5% 5 100 10000000 = 500000 立 =0.5 M立 Therefore this resistor has a value between 9.5M立 and 10.5M立 Question 2: a) 1.75 k立 賊2% 1.751000= 1750 立 According to the Colour codes 1=brown, 7= violet, 5=green, brown= 2 and red is 2% The colour code is {Brown, Violet, Green, Brown, and Red} b) 10M立 賊5% 10106= 10000000 立 According to the colour codes 1= brown, 0= black, 6= blue and gold is 5% The colour code is {Brown, Black, Blue, and Gold}
  • 3. 3 c) 38k立 賊5% 381000= 38000 According to the Colour codes 3= orange, 8= grey, 3= orange and gold is 5% The Colour code is {Orange, Grey, Orange, and Gold} Equipment used Power supply Digital Multimeter (DMM) which serves as a Voltmeter and Ammeter Three carbon resistors with different resistances Two conductors Procedures To Measure Voltage: Change the voltage selection knob on the DMM to (DC or V) for DC measurement. Voltage is measured in parallel with the load and the range of your measurement can be altered by using the Range buttons. To Measure Current: Change the current outlet of the DMM to (+ terminal) and the COM outlet (ground). Current is measured in series you will have to break the circuit to measure current. For a current less than 200mA use the outlet (V立A) and for current greater than 200mA use the outlet written 20A in red else the DMM will not be accurate and may not show the current reading. You can vary the range of your measurement by using the Range buttons. To Measure Power Supply Voltage: A voltmeter is always connected in parallel across your load or power supply. The + terminal of the voltmeter should be connected to the + terminal of the Power Supply hence forth referred to as (PS) (usually the red outlet) and the - terminal of the voltmeter to the - terminal of the PS (usually the COM or black outlet) of the DMM. Part 1 of the lab 1. Push the power button to turn on the multi-meter. 2. To use the DMM as an ohmmeter, turn the knob so that it points on the side of resistance, where there is (立) symbol. 3. Get three resistors from your toolbox.
  • 4. 4 4. From the colour code of each resistor, determine the resistance and the tolerance of each resistor. 5. Calculate the range of resistance values for each resistor based on the tolerance of the resistors. 6. These results were recorded on the table provided. 7. Using the DMM, measure the resistance of each resistor. 8. To do this try to seek advice from the laboratory assistant (insert a red banana-to-clip connector into the 立-plug and a black banana clip connector into the COM-plug). Place the resistor-under-test between the red and the black connectors. 9. Record this on the table provided. Part 2 of the lab 1. Set the Meter knob of the PS to the +5 V position, and connect the two wires from the PS (+ V and COM outlets) to the voltmeter. 2. Since youre measuring DC voltage, press the --V button and maximum range on your Multimeter. 3. Adjust the output of the PS by using the Voltage +5 V knob. 4. Check your voltage by reading the volts scale of your PS (lower reading) and compare it to the voltmeter reading. Results Part 1 results: Measuring Resistance Exercise Calculations using Equation (1) % Error R1= 560 570 560 100 = -1.79% R2= 2727.2 27 100 = -0.74% R3= 4746 .9 47 100 = 0.2% Table 1 Resistor Colour Codes Value of resistance calculated from colour code Measured value or resistance % Error R1 Green, Blue, Brown, Gold 560立 賊5% 570立 -1.79% R2 Red, Violet, Black, Gold 27立 賊5% 27.2立 -0.74% R3 Yellow, Violet, Black, Gold 47立 賊5% 46.9立 0.2%
  • 5. 5 Table 2 Part 2: Use of Power Supply Exercise Readings from Power Supply and Voltmeter respectively Power Supply Voltmeter 5V 5.05V 10V 9.96V 15V 15.03V 20V 19.9V 25V 24.9V 30V 29.8V Table 3 Discussions Part 1: Tolerance for all the resistors is more or less 5%. The negative percentages just mean that the amount that we have calculated has been exceeded by that percentage, and the positive percentages just mean that the amount that we have calculated has not been exceeded by that percentage. All the errors for each resistance measured fall within the calculated ranges. Therefore the method of calculat ing resistance ranges using colour codes is approximately accurate and can be used as an alternative to measuring the resistances all the time. Part 2: The reason why the voltmeter readings are slightly lower or bigger is because the power supply has an internal resistance. Within the conductors energy is converted into other forms of energy such as (heat) causing the voltage drop. This affects the potential difference as proven above with table number 3. Conclusion: In conclusion I have learned how to operate the DMM and that making the use of colour codes to calculate the resistance of a resistor is faster than actually measuring that resistance. The errors due to these calculations is very small and is within the range of resistivity of the resistor. There is also the matter of the conversion of electricity from one form to another that I have noticed while doing the last exercise in which the voltage readings are quite different from the real ones. This is due to
  • 6. 6 the elements that contribute to the resistance namely (length of conductor, material of conductor, cross sectional area of the conductor and the material from which the conductor is made from). Furthermore I think that these findings were useful in the sense that I now understand more about electrical circuits than before these lab and that it will contribute to the foundation of my engineer ing career.