Villanova University
ECE 2053 Fundamentals of Electrical Engineering I Lab
Spring 2005
1 – Basic Instrumentation and Measurements
Learning Objectives:
1.
2.
3.
4.
5.
At the end of this session you should be able to:
Use the digital multimeter for dc voltage measurements
Use the digital multimeter for dc current measurements
Set the dc power supply for different voltages
Use the resistor color code
Use the digital multimeter to measure dc resistance using the 2-wire method
Parts List
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Digital Multimeter (Agilent model 34401A)
Triple Output DC Power Supply (Agilent model E3631A)
# 47 lamp
Prototyping board (PB)
Wire stripper
Needle nose pliers
Hook up wire
Small DC motor
Resistors: 1200, 1500, 2200, 2700 all 5%, ¼ W
Exercise 1: Digital Voltmeter and DC Voltage Measurements
The top instrument at the right of your lab bench is the digital multimeter (abbreviated
DMM). It measures voltage, current and resistance. Press the Power button – the DMM can be
left on for the lab session.
How to Make DC Voltage Measurements. Press the DC V button. Verify that the red probe
plugs into the HI jack and the black probe plugs into the LO jack. To make a measurement,
connect the tip of the red probe and the tip of the black probe to points (called nodes) where you
expect a 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.
The unit for voltage is the volt (symbol V – upper case). Smaller units of voltage are
the millivolt (10-3 volt) which has the symbol mV, and the microvolt (10-6 volt) which
has the symbol μV.
You may want to review the document Quick Start on the DMM which is on your lab bench.
Exercise 2: Digital Ammeter
How to Make DC Current Measurements. Press the the Shift DC I buttons (I stands for
current). Verify that the red probe plugs into the I jack and the black probe plugs into the LO
jack. To make a current measurement, the tip of the red probe and the tip of the black probe
must be inserted in series with the element whose current is to be measured. A positive meter
reading means the point where the red tip is connected has current entering it.
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The unit for current is the ampere (symbol A – upper case). Smaller units of current
are the milliampere (10-3 ampere) which has the symbol mA, and the microampere
(10-6 ampere) which has the symbol μA.
Exercise 3: Prototyping Board
1. The image shows a prototyping board (PB) whereupon circuits are built. The PB is shown in
the landscape orientation which I recommend. First note the vertical strip on the left – this is
referred to as a buss. It has 2 columns of holes; all of the holes in each column are
electrically connected. Next note there are 4 more busses on the PB, oriented horizontally.
DC power is usually connected to the busses. Between each horizontal buss is a socket strip
with a gutter running down the center. On one side of the gutter is an area of 5 rows by more
than 50 colums. The 5 holes in each column are electrically connected.
Exercise 4: DC Power Supply
On your lab bench is a dc power supply, the Agilent model E3631A. The power supply (PS)
has three independent (and variable) dc voltage sources: a + 25 volt supply, a – 25 volt supply,
and a 6 volt supply. Each supply has a current limit which can be set by the user.
1. Press the Power On button. The display should read OUTPUT OFF. The power supply
defaults to the + 6 volt supply. Small annunciators give the operating status of the PS. For
example, if the + 6 volt supply is operating in constant voltage mode then the +6V
annunciator and the CV annunciator will be on. If the power supply is remotely controlled,
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then the Rmt annunciator will be on. The power supply can also be used in a constant
current mode; in that case the CC annunciator would be on.
2. Press the Display Limit button. The left hand side of the display shows the voltage of the
PS, and the right hand side of the display shows the current limit of the PS.
3. Press the Output On/Off button. If the OFF annunciator is lit, the three power supply
outputs are disconnected from the front panel connectors of the PS.
4. For constant voltage operation press the Output On/Off button to make sure the annunciator
reads OFF.
5. Let's initially set the + 6 volt supply for a constant voltage of 0.68 volts. Press the Display
Limit button. The Lmt annunciator blinks indicating that the display is in the limit mode and
the knob at the right is set for voltage adjustment. The second digit of the voltmeter display
will be blinking. Set the blinking digit to a 6 by rotating the knob. (Check that the Lmt
annunciator still blinks.)
Note: If the display times out press the Display Limit button again.
6. Next press the right arrow button to move the blinking digit to the right. Change the blinking
digit to an 8.
7. Set the current limit to 1.20 amperes – this value will limit the current of the PS in the event
the terminals are accidentaly shorted. To do this, press the Voltage/Current button so the
current display is blinking. Use the knob to adjust the current limit to 1.20 A.
Exercise 5: Voltage – Current Measurements of a Lamp
1. Obtain a #47 lamp and socket. Plug the wires into 2 holes on your PB – call the holes N1
and N2.
2. Set the DMM for current measurement as follows. Plug the red probe into the I jack and the
black probe into the LO jack. Press the Shift DC I buttons. Note that I is the symbol for
current.
3. Get a piece of red wire and connect one end to the positive terminal of the + 6 volt supply
and the other end to a hole on the PB that is electrically connected to N1. Connect the tip of
the red probe of the DMM to N2.
4. Get a piece of black wire and connect it to the tip of the black probe of the DMM. Connect
the other end of the black wire to the negative terminal of the + 6 volt supply. The circuit
that you have just wired is a series circuit consisting of the PS, an ammeter, and a lamp.
5. Make a sketch of the circuit in your notebook.
6. Press the Output On/Off button to connect power to the lamp. Set the PS for a voltage of 6.0
volts. The ammeter should display a reading. If not, it may be because the ammeter fuse is
blown – see your instructor.
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7. Record the the lamp voltage from the PS display and the current from the digital ammeter.
8. Repeat the above for PS voltages from 0.5 up to 5.5 V in increments of 0.5 V. Note and
record the voltage when the lamp lights. Put all of your data in tabular form – see Table 1 in
the Appendix for an illustration of a data table.
9. Make a graph, in your notebook, with voltage on the abscissa (x-axis) and current on the
ordinate (y-axis). Plot the recorded, and draw a smooth curve through the data points. This
is referred to as the i-v characteristic for your lamp (see page 62 of Franco). Label the axes
of the graph and place a Title at the top of the graph. Show this to your instructor.
10. Compute the power absorbed by the lamp, in milliwatts, for a voltage of 3.0 and 6.0 volts.
11. Press the Output On/Off button on the PS to disable the outputs.
Exercise 6: Voltage – Current Measurements of a DC Motor
1. Obtain a small DC motor and connect this to your PB in place of the lamp/socket unit.
2. Set 0 volts on the PS. Then press the Output On/Off button on the PS. Increase the PS
voltage by slowly rotating the Ps knob until the motor starts to run.
3. Record the voltage and the current, and compute the power absorbed by the motor.
4. Repeat the above for PS voltages of 4.5, and 6.0 volts. Put your data in tabular form similar
to Table 2 shown in the Appendix.
5. Press the Output On/Off button on the PS to disable the outputs. Then remove the motor.
Exercise 7: Resistance and Resistors
The resistance of a conductor is defined as the ratio of voltage, V, across the conductor to the
current, I, through it. The unit is volt/ampere which is defined to be an ohm, with the symbol .
How to Make DC Resistance Measurements. Press the Ω 2 W button. Verify that the red
probe plugs into the right hand "HI jack" and the black probe plugs into the right hand "LO jack".
Note: The symbol Ω 2 W found on the front panel of the DMM means a resistance
measurement using two wires (the red and black probes). Most of our measurements do not
require the four wire technique.
To make a measurement, connect the tip of the red probe and the tip of the black probe to two
points where a resistance measurement is required – make good electrical contact.
The unit for resistance is the ohm (symbol Ω). Larger units of resistance are kilohm
(1000 ohms) which has the symbol kΩ, and megohms (1,000,000 ohms) symbol MΩ.
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1. Examine the i-v curve for the #47 lamp that you plotted for the lamp. Calculate the
resistance of the lamp, using Ohm’ law, at these voltages: 1.3, 2.3, 3.3, 4.3, 5.3 and 6 volts.
Put the results in tabular form.
2. Connect the two DOM leads across leads of the lamp. Record the resistance of the lamp.
Note: Make good connections with the clip leads—Do not hold the clips with your fingers.
There are differences in the results from step 1 and 2. In step 2 you determined the cold
resistance of the bulb, while in step 1 you measured the hot resistance of the bulb
(remember, there was current passing through the bulb!).
3. Now measure the resistance between your hands—let your partner try it. The readings will
be erratic because body resistance varies with finger pressure and moisture.
4. Select a ¼ -watt resistor with a nominal value between 1000 and 3300 ohms. Note its color
code. Refer to the handout on resistors and color codes. From the color code, determine its
nominal value and resistance tolerance. Record these values along with the color code.
Note: This web site, www.ee.upenn.edu/rca/calcjs.html, at the University of Pennsylvania,
Philadelphia, has a nifty resistor color code calculator.
5. Use the DMM to measure the resistance of the resistor. Record the reading. Does the
reading fall within the tolerance?
Appendix
A1. Examples of Data Tables
Table 1: Lamp Data
Lamp Voltage
(volts)
….
….
Lamp Current
(milliamperes)
…
…
Lamp Condition
(on, off)
Calculated Power
(milliwatts)
…
…
Table 2: Motor Data
Motor Voltage
(volts)
…
…
Motor Current
(milliamperes)
…
…
Motor Running
(yes, no)
Calculated Power
(milliwatts)
…
…
A2. Modes of Operation of the Triple Output Agilent Power Supply
There are two modes of operation of this power supply: the limit mode and the meter mode.
The default mode of operation of the power supply is meter mode. This means that the display
shows the actual output voltage and current of the supply.
When you press the Display Limit button, the display shows the limit mode of operation. The
present limit values (the user sets these) of the selected supply will be displayed and the Lmt
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annunciator will blink. In this limit mode, you can set the limit values of voltage and current by
adjusting the knob at the right. If you press the Display Limit button again (or let the display
time-out after several seconds) the display will return to the meter mode and the Lmt annunciator
turns off.
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