Download Lab Experiment I

L. Fennigkoh, Ph.D.
Milwaukee School of Engineering
Electrical Engineering & Computer Science Department
EE-2705 – Linear Circuits I: DC
Experiment 1
Use of Electrical Test and Measurement Instruments:
Series and Parallel Circuits
Name:
Lab Partner:
Date:
Objectives:



To become proficient in the safe and proper use of the Agilent 34401 digital multimeter and
E3631A DC power supply.
To become proficient in the use of electrical circuit breadboarding techniques.
To recognize and be able to construct series and parallel circuits.
Needed Equipment and Parts:


Before coming to lab, go to Tech Support and
check out the following (one set per two person
team): breadboard, parts box, and hook-up
wire.
Review the previously distributed Power Supply
Quickguide
Use of the Digital Multimeter and Power Supply:
DC Voltage Measurements:
1. Turn on the multimeter and power supply. Using the
Output On/Off key, verify that the power supply’s
output is OFF. Use this key anytime you wish to
disconnect the power from your circuits without
having to unplug leads.
2. Be sure that the leads to the multimeter are connected
properly to measure voltages – red to Hi Input, black to
Lo input. Then connect the multimeter to the +6 volt
terminals on the power supply (red to +, black to -).
Remember: voltages are always measured across
terminals or components.
3. Press the Output On/Off key on the power supply to turn
the output on. Use the < > arrow keys in conjunction
with the ADJUST knob to set the output to 5.000 VDC.
Verify that multimeter is reading the same value. Change the voltage level and notice how the
multimeter should track these changes.
1
4. Turn the power supply off.
Resistance Measurements:
1. To measure resistance, select the Ω 2W key. Randomly select four resistors from your parts
box - making sure that each resistor is at least 330 ohms or larger and less than or equal to
4.7K ohms. Record the resistance and tolerance as revealed by their color code and arbitrarily
assign them the labels R1-R4 in the table below. Then place the multimeter leads across each
resistor to measure their resistance exactly. (Avoid touching at least one end of the test probes
with your fingers). Record these values in the table and calculate their percent error. Are the
resistance values within their stated tolerances? Do not put these resistors back in the parts
box as they will be used again shortly.
Circuit Label
Resistor color
bands:
Color code
value
(ohms):
Tolerance (%):
R1
Resistance Measurements
R2
R3
Measured value
(ohms):
Error (%):
((actual – rated)/rated)100
Electrical Measurements from Breadboarded Circuits:
1. As shown in the accompanying figures, the breadboard is a
convenient circuit construction and development tool.
It
contains a multitude of electrically-connected sockets that allow
components and hook-up wires to be connected without
soldering.
Connections to the breadboard from other
instruments, e.g., digital multimeter, power supply, etc. may be
conveniently made through the red and black banana jacks
shown. These jacks are also internally connected to the
adjacent sockets shown.
The individual sockets are internally connected as shown below.
Be sure to pay particular attention to this when wiring your
circuits.
2
R4
In general, it is best to keep all circuit power supplies disconnected from the
breadboard until you are finished with the wiring and have verified that all connections
have been properly made.
2. Using the breadboard and four resistors previously selected,
construct the circuit shown. In general and when possible,
always follow established color codes when wiring such
circuits, e.g., (+) red-to-red, (-) black-to-black.
Again, and as shown, the banana jacks are connected internally to the
adjacent small connectors. You may use hook-up wire to make a
connection from this small connector to the breadboard, or insert
components directly in this small connector. As also shown in the
adjacent photo, note that all breadboard connectors within the ovals
are electrically connected. When constructing circuits in this way, it is
generally best to keep the number of interconnections to as few as
possible, i.e., keep your use of jumper wires to a minimum. You
should feel a slight mechanical resistance when inserting either
components or wires into the holes on the breadboard – if not, select a
different hole as worn contacts could create circuit problems. You may
also stack the banana plugs together, e.g., all circuit common connections (black-to-black,
etc.). DO NOT apply power to the circuit at this time.
Never attempt to make resistance measurements across components in powered
circuits – to do so may damage the multimeter. Such in-circuit measurements may also
be inaccurate due to other parallel component influences.
3. In the space provided – or directly within your notebook - and neatly showing all calculations,
determine the total circuit current based upon both the measured values of your resistors and
that expected based on their rated values. Also, determine percent difference between the
actual and rated values. (if these calculations were not directly entered into your notebook, cut
and paste this table into your notebook).
Calculated total current based on
measured resistor values
IT =
mA
% difference from expected:
[(measured-rated)/(rated)]*100
3
Calculated total current based on
rated resistor values
IT =
mA
4. Similarly, calculate the expected voltage drops across each resistor based upon their
measured and rated resistor values. (again, either directly in your notebook or cut and paste
this completed table).
Calculated voltage drops based on measured and rated resistor values
R1
R2
R3
R4
Measured:
Rated:
% Difference:
(actual vs rated)
5. Verify again that your circuit is properly wired. Then, with the power supply on and set to 5.00
volts DC, connect your circuit.
6. With the DMM set to measure DC volts, measure the actual voltage across each resistor –
noting the appropriate position of the red and black leads. Record these measured values in
the table above.
7. Turn the power supply output to OFF.
8. Using the actual resistance and voltage measurements recorded above, calculate the power
being dissipated by each of the resistors. Are the resistors properly rated for the power being
dissipated? YES / NO
R1
Calculated power dissipation (watts)
R2
R3
R4
9. Verify that the total power being delivered by the power supply is equal to the sum of the
power being absorbed by each of the resistors.
4
Circuit Current Measurements
1. Follow the instructions listed below then configure the DMM to measure total DC circuit
current. Once you have the DMM properly connected, turn the power supply’s output on
and note the measured current. Record its value here: _________________
If you have no reading from the DMM when attempting to measure current, check fuse located
on the rear panel of the DMM. Get a replacement from Tech Support if necessary.
2. Calculate the percent differences between what you predicted earlier and what you just
measured.
5
Circuit No. 2
1. Using the exact same four resistors, reconfigure your
circuit to that shown in the adjacent figure. Do not
power up the circuit at this time.
2. Using both your actual and rated resistor values, calculate:
6

The total circuit resistance as seen by the power supply;

The total current that must be provided by the 5 volt power supply;

The current flowing through R1 and R2;

The current flowing through R3 and R4

The voltage drop across each resistor.

Using Kirchhoff’s Voltage Law, show how you could determine the value of Vo knowing
each of the resistor voltage drops determined above.
3. Power up the circuit and measure each of the resistor voltage drops and the value of Vo.
Record these values in the table shown.
Calculated & measured voltage drops based on actual and rated resistor
values
R1
R2
R3
R4
Vo
Rated:
Measured:
4. Reconfigure the DMM to measure DC current. Similarly, measure the total circuit current, and
the individual branch currents, i.e., current through R1 and R2, and R3 and R4. How do these
measured values compare with what you calculated above?
7
Individually, answer the following:
Questions:
1. Using your collected data, explain which specific circuit laws have been demonstrated though
this experiment.
2. If, in circuit no. 2, all of your resistor values were exactly the same in value, what would be the
value of Vo and why?
3. In using the DMM for either current or voltage measurements, did connecting the meter to the
circuit affect any of your measurements? That is, when and why may have some of your
measured values differed from your calculated values – even when actual component values
were used?
.
8