NATIONAL UNIVERSITY OF TECHNOLOGY (NUTECH)
DEPARTMENT OF ELECTRICAL ENGINEERING
EXPERIMENT# 01
Introduction to the Lab Equipment
Objective
•
To familiarize with voltmeter
•
To familiarize with Ammeter
•
To understand the resister color coding
Theoretical Explanation
Breadboard
A breadboard is a construction base for prototyping of electronic circuits. Because the solderless
breadboard does not require soldering, it is reusable. This makes it easy to use for creating
temporary prototypes and experimenting with circuit design.
Many electronic components have long metal legs called leads. Almost all components withleads
will work with a breadboard. Breadboards are designed so you can push these leads into the holes.
They will be held in place snugly enough that they will not fall out but are lose enoughthat you
can pull them out easily.
Interconnects of Breadboard
Remember that the inside of the breadboard is made up of sets of five metal clips. This means
that each set of five holes forming a half-row is electrically connected as indicated by theblue
box. Two parallel buses on the opposite side of the breadboard are not electrically connectedto
each other. Typically, they are used to make power and ground available on both sides of the
breadboard.
This image shows which holes are electrically connected in a typical Full-sized breadboard,
NATIONAL UNIVERSITY OF TECHNOLOGY (NUTECH)
DEPARTMENT OF ELECTRICAL ENGINEERING
The figure below shows resistors connected in series with power supply connected across
them.
The figure below shows resistors connected in parallel with power supply connected across
them.
How to Make DC Current Measurements:
•
Rotate the knob to A.
•
Verify that the red lead plugs into the A (or mA) jack and the black lead plugs into the COM
jack.
•
To make a current measurement, the tip of the red lead and the tip of the black lead must be
inserted in series with the element whose current is to be measured.
NATIONAL UNIVERSITY OF TECHNOLOGY (NUTECH)
DEPARTMENT OF ELECTRICAL ENGINEERING
•
A positive meter reading means the point where the red tip is connected has current entering
it.
NOTE: The unit for current is the ampere (symbol A – upper case). Smaller units of currentare
the milliampere (10-3 (10 ampere) symbol mA, and the microampere 10-6) symbol μA.
Think about the changes you would have to make to a practical circuit in order to include the
ammeter. To start with, you need to break the circuit so that the ammeter can be connected in
series. All the current flowing in the circuit must pass through the ammeter. Meters are not
supposed to alter the behavior of the circuit, or at least not significantly, and it follows that an
ammeter must have a very LOW resistance.
How to Make DC Voltage Measurements
•
Rotate the knob from OFF to V.
•
Verify that the red lead plugs into the V jack and the black lead plugs into the COM jack.
•
To make a measurement, connect the tip of the red lead and the tip of the black lead across
the points where you want to measure voltage (potential difference).
•
A positive meter reading means the point where the red tip is connected is higher in voltage
than the point where the black tip is connected.
NOTE: The unit for voltage is the volt (symbol V). Smaller units of voltage are the millivolt
NATIONAL UNIVERSITY OF TECHNOLOGY (NUTECH)
DEPARTMENT OF ELECTRICAL ENGINEERING
(10-3 volt) symbol mV, and the microvolt (10-6 volt) symbol μV.
This time, you do not need to break the circuit. The voltmeter is connected in parallel between
the two points where the measurement is to be made. Since the voltmeter provides a parallel
pathway, it should take as little current as possible. In other words, a voltmeter should have a
very HIGH resistance.
How to Make Resistance Measurements
An ohmmeter does not function with a circuit connected to a power supply. If you want to measure the
resistance of a particular component, you must take it out of the circuit altogether and test it separately, as
shown in diagram D:
NATIONAL UNIVERSITY OF TECHNOLOGY (NUTECH)
DEPARTMENT OF ELECTRICAL ENGINEERING
Ohmmeters work by passing a small current through the component and measuring the voltage
produced. If you try this with the component connected into a circuit with a power supply,the most
likely result is that the meter will be damaged. Most multi-meters have a fuse to help protect
against misuse.
How to Make Resistance Measurements using Colour Coding
The use of Resistors Colour Bands is the most common system for colour coding carbon resistors. Colour
bands are printed at one end of the insulating body. Reading from left to right, the first band is close to
the edge gives the first digit in the numerical value of R. the next band marks the seconddigit. The
third band is the decimal multiplier, which gives the number of zeroes after two digits.In some
resistors first three bands represent the digits and fourth band is decimal multiplier.
The amount by which the actual R can be different from the color-coded value is the tolerance,
usually gives in percentage. For instance, a 1000ohm resistor with -+10% tolerance can have
resistance 10% above or below the coded value. This R, therefore, is between 900ohm and
1100ohm.
In four band resistor the 4th band and in five band resistor, the 5th band is tolerance band.
NATIONAL UNIVERSITY OF TECHNOLOGY (NUTECH)
DEPARTMENT OF ELECTRICAL ENGINEERING
In case of four-color bands, the first two bands are the significant figures of the value, the third
band is a multiplier (number of zeros) and fourth band is the tolerance band, i.e. red black brown
gold would be 2 0 x 10 + 5% or 200+5% ohms.
In case of five color bands first three bands are the significant figures of the value, the fourthband
is a multiplier, and fifth band is the tolerance band.
NATIONAL UNIVERSITY OF TECHNOLOGY (NUTECH)
DEPARTMENT OF ELECTRICAL ENGINEERING
In case of six color bands the sixth band is the temperature coefficient band. Following tables
give the values allocated to different colors to find the value of a resistor through the colorbands
it has on it.
The resistance value of the resistor is not the only thing to consider when selecting a resistorfor
use in a circuit. The "tolerance" and the electric power ratings of the resistor are also important.
The tolerance of a resistor denotes how close it is to the actual rated resistance value.For example,
a ±5% tolerance would indicate a resistor that is within ±5% of the specified resistance value. The
power rating indicates how much power the resistor can safely tolerate. Themaximum rated power
of the resistor is specified in Watts. Power is calculated using the square of the current (I2) x the
resistance value (R) of the resistor. If the maximum rating of the resistor
NATIONAL UNIVERSITY OF TECHNOLOGY (NUTECH)
DEPARTMENT OF ELECTRICAL ENGINEERING
is exceeded, it will become extremely hot and even burn. Resistors in electronic circuits are
typically rated 1/8W, 1/4W, and 1/2W. 1/8W is almost always used in signal circuit
applications. Note, the IEC standard replaces the decimal point with the engineering prefix,
thus 1.2 k is alternatelywritten 1k2.
Example:
Mnemonics:
A useful mnemonic for remembering the first ten color codes matches the first letter of thecolor
code, by order of increasing magnitude.
•
B.B.ROY is in Great Britain with Very Good Wife.
•
Examples:
•
A resistor with a color-coded of “Red-Violet-Orange-Silver” would have a colorcoded value of 27 kΩ.
The color -coded tolerance of silver band is ±10%, and 10% of 27 kΩ is 2.7 kΩ. This
meansthe resistor should have an actual measured value within the range of 27 k Ω –
2.7 kΩ = 24.3kΩ and (27 kΩ + 2.7 kΩ = 29.7 kΩ ).
•
NATIONAL UNIVERSITY OF TECHNOLOGY (NUTECH)
DEPARTMENT OF ELECTRICAL ENGINEERING
Experiment Procedure
Given the color codes in Table below, determine and record the nominal value, tolerance
and the minimum and maximum acceptable values.
NATIONAL UNIVERSITY OF TECHNOLOGY (NUTECH)
DEPARTMENT OF ELECTRICAL ENGINEERING
Given the nominal values and tolerances in Table below, determine and record the corresponding
color code bands.
NATIONAL UNIVERSITY OF TECHNOLOGY (NUTECH)
DEPARTMENT OF ELECTRICAL ENGINEERING
Comments