ELCT708: Electronics for Biotechnology

Transcription

1 ELCT708: Electronics for Biotechnology Lab Report 1 Name: Group:

2 Part 1 Introduction Electrical Quantities Objective: The objective of this experiment is to learn different electrical properties as Current, Voltage, Resistance and Power. Theory: 1. Current: (i or I) is the flow of electric charge from one point to another, and it is defined as the rate of movement of charge past a point along a conduction path through a circuit, or i = dq/dt. The unit for current is the ampere (A). One ampere = one coulomb per second. Note: To measure the current we use Ammeter.Some ammeters are fabricated and used to measure current only while others are fabricated in a multimeter to be used to measure other electrical parameters too. Ammeter must be connected in series to the resistance in which current is to be measured therefore it must be of very small resistance not to affect the current passing in this resistance i.e. Ammeter = zero but since there is no ideal case ever therefore the practical ammeter have a certain small resistance. 2. Voltage: (v or V) is the "potential difference" between two points, and it is defined as the work, or energy, required for moving a charge of one coulomb from one point to another. The unit for voltage is the volt (V). One volt = One joule per coulomb. 2

3 Note: To measure the voltage we use voltmeter.some voltmeters are fabricated and used to measure voltage only while others are fabricated in a multimeter to be used to measure other electrical parameters too. Voltmeter must be connected in parallel to the resistance across which voltage is to be measured therefore it must be of very large resistance not to withdraw current from resistance and therefore not to affect it s voltage. Ideally, voltmeter resistance Voltmeter = but since there is no ideal case ever therefore the practical voltmeter have a certain large resistance. 3. Resistance: (R) is the "constant of proportionality" when the voltage across a circuit element is a linear function of the current through the circuit element, or V = IR. A circuit element which results in this linear response is called a resistor. The unit for resistance is the Ohm (). One Ohm = one volt per ampere. The relationship V = RI is called Ohm's Law. Note: To measure the Resistance we use Ohmmeter.Some Ohmmeter are fabricated and used to measure resistance only while others are fabricated in a multimeter to be used to measure other electrical parameters too. To measure the resistance, the resistance must be disconnected from the circuit in which it lie in and then connected across the Ohmmeter to measure its resistance. Never measure the resistance when Power supply is ON. 4. Power: (p or P) is dissipated in a resistor in the form of heat. The amount of power is determined by: P=VI, P=I 2 R, or P=V 2 /R. The latter two equations are derived by using Ohm s Law (V = RI) and making substitutions into the first equation for power. The unit for power is the watt (W) One watt = one joule per second. Note: To measure the Power we get voltage across the resistance and current passing through it then use the law to get value of DC power. 3

4 Measuring Instruments The multimeter used in our lab is shown in the figure 1. Figure 1 It has two ranges for DC voltage measurements which are V (volts) and mv (mill volts). It can measure current by setting it to ma where the displayed measurement will be in ma and can measure resistance if it is set to. 4

5 Resistor Color Code Objective: The objective of this experiment is to allow you to read the color code of a resistor. Including the tolerance. Introduction: How can the value of a resistor be worked out from the colors of the bands? Each color represents a number according to the following scheme: Number Color 0 black 1 brown 2 red 3 orange 4 yellow 5 green 6 blue 7 violet 8 grey 9 white The first band on a resistor is interpreted as the FIRST DIGIT of the resistor value. For the resistor shown below, the first band is yellow, so the first digit is 4: The second band gives the SECOND DIGIT. This is a violet band, making the second digit 7. The third band is called the MULTIPLIER and is not interpreted in 5

6 quite the same way. The multiplier tells you how many zeroes you should write after the digits you already have. A red band tells you to add 2 zeroes. The value of this resistor is therefore ohms, that is, 4700, or 4.7K. Work through this example again to confirm that you understand how to apply the color code given by the first three bands. The remaining band is called the TOLERANCE band. This indicates the percentage accuracy of the resistor value. Most carbon film resistors have a goldcolored tolerance band, indicating that the actual resistance value is with + or - 5% of the nominal value. Other tolerance colors are: When you want to read off a resistor value, look for the tolerance band, usually gold, and hold the resistor with the tolerance band at its right hand end. Reading resistor values quickly and accurately isn't difficult, but it does take practice! 6

7 Breadboard and Wiring Objective: The objective of this experiment is to be familiar with breadboard and connection made on it. Introduction: In this lab you ll use a breadboard to implement simple circuits consisting of resistors, capacitors, inductors, diodes, and various integrated components. Breadboards provide you with a general wiring fabric in which to make connections among circuit components. Learning how to use this wiring fabric effectively takes time and, more vital, practice. Figure 2 shows you the basic layout of the breadboards you ll be using. Figure 2: Basic Breadboard As you can see, the surface of board is covered in pinholes into which you can insert wires or electric component leads. Beneath the plastic surface, the holes are connected with a network of metal tabs. But not all pinholes are connected together. Every row in each of the two main columns is wired together. [Note: The rows are NOT connected across the column.] You can also see a series of pinhole groups arranged in columns along the left and right 11 sides of the board. These are useful for wiring global signals and power supply voltages. 7

8 Figure 3: Special Sections for Global Signals Making a connection between two components is simple once you understand the internal wiring of the board. Let s take a simple example of connected two resistors in series or in parallel. The general wiring fabric of the breadboard provides an unlimited number of possibilities, but we want to focus on the efficient implementations. Never use more jumper wire than necessary! Let the breadboard do the work for you. Figure 4: Basic Wiring Combinations Figure 5 shows 3 examples of series wiring and 2 examples of parallel wiring. The pinholes where the component leads connect to the board are exaggerated with big circles. 8

9 Figure 5: Example Uses of the Breadboard These few examples show you the basics and give you enough knowledge to do the labs. A few general points to remember when you begin wiring a circuit: Try to use the breadboard to make connections, i.e. avoid the use of extra jumper wire. Murphy s Law tells us that the more wire you use; the more likely you are to make an error by shorting two wires or incorrectly wiring the circuit. When you use extra jumper wire, keep it as short as possible. The lab kits provide jumper wire of various lengths. Use them all! A mess of long wires creates the St. Louis Arch syndrome, where all your wires make glorious arches over each other. Now you can t be expected to appreciate why these arches are electrically undesirable (They act as antennas), but you can appreciate how easily they complicate your life. If your circuit looks like a bush of wires, imagine how hard it will be to debug it when [Note: not if] it doesn t work correctly. Keep related components together. Make the circuit on the breadboard look as much as possible like the schematic you re implementing. The visual correspondence will help you 9

10 differentiate the various nodes; plus, your TA can do more to help you debug if he can easily make sense of your circuit. All dots in each line are electrically connected 10

11 Com3Lab Master Unit Contents: The Master unit is shown in the figure below. It consists of: 1. Two multimeters. 2. Function Generator. 3. Oscilloscope. 4. Digital Analyzer. These parts are declared in the figures below: 11

12 To start using the Master Unit switch ON the Unit by pressing the ON/ OFF switch. Multimeters: The multimeters can measure voltage or current or resistance, just set the mode to the required quantity and then connect it in the proper way and get reading from the display. 12

13 Function Generator: There are two keys in the function generator part: The Function Key: It is used to choose between: 1. Square wave. 2. Sinusoidal wave. 3. Triangular wave. 4. DC signal. The Mode Key: It is used to control the parameters of the selected function. In case of: a. Sinusoidal wave, the Mode key chooses between frequency in khz, Peak to Peak voltage and DC level superimposed on the signal. b. Square wave, the Mode key chooses between frequency in khz, Peak to Peak voltage and DC level superimposed on the signal. c. Triangular wave, the Mode key chooses between frequency in khz, Peak to Peak voltage and DC level superimposed on the signal. d. DC mode, the Mode key has no use. Note that: The DC power supply is used to generate either a constant voltage (CV) or a constant current (CC). In our lab, we use the DC power supply to generate CV only, which gives an output range from -10 volt to 10 volt. You must press function and set it to DC to get constant voltage. To use this voltage source, the ground of the circuit must be connected to the ground of the voltage source and then use the OUT terminal to be connected to the circuit as the positive pole of the voltage source. To get a certain voltage within the specified range rotate the rotating knob until you obtain it. These are the part that will be of great use in the DC electric circuit s lab. The Oscilloscope and the Digital Analyzer will be explained when needed. 13

14 Part 2 OHM S LAW Introduction: The relation between the voltage across a certain resistor and the current flowing through it is governed by Ohm s Law, which states that The potential difference (voltage) across an ideal conductor is proportional to the current passing through it. The constant of proportionality is called the "resistance", R. Ohm's Law is given by: V = I R Where V is the potential difference between the two terminals of the resistor, R.I is the current flowing through the resistance. It is often expressed as: Where g is the conductance, g = 1/R. I = g V Materials that obey Ohm's Law are called "ohmic" or "linear", because the potential difference across it varies linearly with the current. Ohm's Law can be used to solve simple circuits. A complete circuit is a closed loop, which contains at least one source of voltage and at least one potential drop. The sum of the voltages around a complete circuit is zero. 14

15 Question (1): Solve for each of the following set of resistor colors: 1. Red, blue, green Brown from To 2. Red, red, black Red from... To 3. Green, red, brown Gold from. To 4. Violet, orange, orange Silver from. To... 15

16 Question (2): 1. Use the Ohmmeter to measure two of the resistors on your bench. 2. Connect the following circuit as shown in the below figure. 3. Set the DC voltage source in the Com3lab master Unit to be 5V. 4. Adjust multimeter 1 of the Com3lab unit to measure the current (I s ) in the resistors. 5. Adjust multimeter 2 of the Com3lab unit to measure the voltage drop (V) across the two resistors R total. 6. Record the measured current and voltage in the following table. Change the voltage source to be 6, 7, 8,9,10 volts. For each value, record (I s ) and (V). 7. Plot the graph between I s and V on the shown graph with the proper scale. 8. Calculate the slope of the line drawn. 9. Compare and comment on the measured value of R total using the ohmmeter and the reciprocal of the slope of the line. Fill in the following table and Draw V R1 versus I then calculate R total from the graph V (V) I (ma) R total =.. Ohms 16