Basic D.C. AVIM 121 Lab 3 Page 1 of 8 rev. 08.09
• Make voltage measurements with the voltmeter function of the multimeter.
• Investigate aiding and opposing voltage sources.
• Measure the effects of internal resistances on the output of a voltage source.
• Use voltage notation in measuring voltage.
Chapter 12, Basic Electronics, Grob
1. Analog Multimeter and Multimeter Operator's Manual
2. Four 1.5 volt Batteries
3. Circuit Board #3
4. Graph Paper
2 Sheets of 10 x 10 to the inch
1 Sheet of 4-cycle semi-log
• A good source of information about the voltmeter is the multimeter operator's manual.
• For your safety, when taking measurements, handle only one probe at a time and do not touch the metal tip of the probe.
• Handle the materials and test equipment very carefully. Keep them away from the edge of the bench so they won't be knocked to the floor and damaged. Prior to applying the voltage be sure that the meter has been set up and connected properly.
• Record all readings and calculations in the data table.
The following exercise will show how batteries react when connected in different configurations. In addition, symbolic notation will be emphasized.
Section A: Voltage Measurement
Record all readings and calculations in the data tables.
1. Set the multimeter function switch to DC volts, and the range switch to a value of at least 1.5 volts. (This might be 1.5 V, 2.5 V, 3 V, or some similar range setting.)
2. Insert the test leads in the proper jacks for measuring DC voltages. The black lead is the common test lead, and it is placed in the jack labeled common or negative. Consult the operator's manual.
3. Identify the negative and positive terminals of a 1.5 volt battery.
4. Attach the common (black) lead of the meter to the negative terminal of the battery.
5. Touch the other test probe to the positive terminal of the battery. If the meter indicates negative or deflects down scale, check your test lead placement and meter settings. If the meter is deflected beyond the full-scale value, remove the probe and increase the range setting.
6. Read the appropriate DC scale of the analog meter. Note that accurate readings are taken from the middle and upper two-thirds of the analog meter scale. If the pointer is deflected into the lower one-third of the scale, then it might be possible to select a different range. To see if this is possible, determine if the meter indicates a value that is less than the value of the next lower range setting. If it does, switch to the next lower range. Record this reading.
7. If difficulty is encountered in reading the analog meter, review the first laboratory exercise.
8. Begin developing safe work habits by using only one hand and one test lead at a time.

Basic D.C. AVIM 121 Lab 3 Page 2 of 8 rev. 08.09
The terminals of the direct current voltage source, in the circuit of Figure 3-10, are labeled with the letters a and b . These letters are a kind of shorthand notation for giving voltage reference points in the circuit.
For example, E ba
means the voltage E at point b with reference to point a . The second letter is always the reference point. E ba
is a plus (+) 1.5 volts.
To verify E ba
through measurement, the negative lead of the voltmeter must always be placed on the reference point or, in this case, on point a , and the positive lead is placed on point b . The meter reading will be plus 1.5 volts.
In the reverse situation, E ab
would be the voltage E at point a with reference to point b . E ab
would be a minus 1.5 volts. To verify this with a voltmeter, the negative lead is placed on the reference point b and the positive lead on point a . The reading would be down-scale, so we would have a minus reading.
It is extremely important that symbolic commands be complied with. That is, when told to determine E ab for the circuit of Figure 3-10, the procedure is to connect the negative lead of the voltmeter to the positive battery terminal (point b) and the positive lead to the negative battery terminal (point a). Granted the analog meter will not function as it was intended, but you complied with the symbolic command. (Even though the analog meter pointer deflected down-scale when connected like this, NO meter damage will result.)
Whether discussing E ab
or E ba or any other similar notation in a circuit, remember that the second subscript is the point of reference and, as such, the negative common lead of the meter is placed on it. Now, the question is, what should be done about the analog meter reading down-scale. Obviously, one cannot tell what the magnitude is unless the meter is deflected up-scale. Therefore, if commanded by notation to obtain the voltage E ab
in Figure 3-10, the meter would be connected as commanded. Note that the meter reads down-scale, and then reverse the meter leads and read the magnitude of the voltage.
Because of the meter lead reversal, a negative sign is placed in front of the answer, i.e. -1.5 volts.
- + - + + - + a b
FIGURE 3-9: Three batteries connected in series aiding and one battery connected in series opposing.
Terminal a
+ b
Terminal
1.5V
R int
Dotted Line Indicates Single Unit
V-Source with Internal
Resistance
Ω
R
Load
V-Meter
Voltage Out Reading =
V
FIGURE 3-10: Test circuit to demonstrate the effect of the internal resistance in a battery.

Basic D.C. AVIM 121 Lab 3 Page 3 of 8 rev. 08.09
Section B: Aiding and Opposing Voltage Sources
Record all readings and calculations in the data table.
1. Connect two batteries in series aiding. That is, connect the negative terminal of one battery to the positive terminal of the other. If connected properly, two terminals, one positive and one negative, will remain. Using the techniques developed in Section A, measure the voltage across both the series connected batteries. Make certain that the range selector is set to an appropriate voltage range.
2. Connect two batteries in series opposing. This means connect the negative terminal of one battery to the negative terminal of the other. If connected properly, two terminals, both positive, will remain. Measure the voltage across this combination.
3. Connect the four batteries in series aiding, and measure the voltage across them. Set the range to at least 10 volts DC.
4. Connect three batteries in series aiding and one battery in series opposing. See Figure 3-9.
M easure the voltage across terminals a and b (E ba
). [NOTE: ‘a’ is the NEGATIVE lead]
5. Parallel two batteries by connecting them so identical terminals are together. That is, positive to positive and negative to negative. It is very important that paralleled batteries not be connected positive to negative in a closed loop; this configuration will damage the batteries. Measure the voltage across the battery terminals of the parallel connection.
6. Now parallel three batteries and measure this voltage.
Section C: Internal Resistance
Suppose a transistor radio is powered with the battery shown in Figure 3-10. As time passes, the internal resistance (R int
) of the battery increases until the voltage, as measured at the battery terminals, is reduced to 0.9 volts. This low voltage causes the sound from the radio to become distorted. Assuming the load resistance (R
L
) which represents the radio remains constant, at what time will the end point voltage of 0.9 volts be reached? To obtain this answer a graph must be constructed.
To simulate the actual playing of the radio over an 8-hour period, different values of internal resistance
(R int
) are inserted in the circuit. Immediately after inserting a resistor, take the voltage reading. Remove this resistor and reinsert another resistor and take the voltage reading. Repeat this process for all of the resistors listed. Record all measurements and calculations in the data table.
1. Construct the circuit of Figure 3-10 and connect the voltmeter across the 10 k Ω load resistor (R
L
).
After each substitution for R int
, record the voltage reading (V
O
across R
L
) in the data table. (1)
4.7
Ω (2) 10 Ω (3) 100 Ω (4) 470 Ω (5) 1k Ω (6) 1.5k
Ω (7) 2.2k
Ω (8) 2.7k
Ω (9)
3.9k
Ω (10) 4.7k
Ω (11) 5.6k
Ω (12) 6.8k
Ω
2. Using 10 x 10 to-the-inch graph paper, plot the voltage developed across R
L
(see Data Table,
Step 1, E o
column) versus the elapsed time (See Data Table Elapsed Time Column). Use the vertical axis for voltage and the horizontal axis for time. Determine the end point voltage of the battery from this graph.
The coordinate points placed on the graph paper should be identified by placing a circle, square, or triangle around them. The curve does not go through all the points but rather averages them.
See Figure 3-11.
3. From the graph constructed in Step 2, determine the time that an end-point voltage equal to 0.9 volts occurs.
4. Using 4-cycle semi-log paper, construct a graph of the voltage across the load V
O
(use the linear axis) and the internal resistance R int
(use the log axis). In the construction of this graph, use 1 ohm and 0.8 volts as the starting point (origin) and the values of V
O
and R int
from the data table of
Step 1.

Basic D.C. AVIM 121 Lab 3 Page 4 of 8 rev. 08.09
The coordinate points on the graph should be identified by placing a circle, square or triangle around them, as shown in figure 3-11(a). Notice that the curve does not go through al the points but rather averages them. Figure 3-11 (b) is an incorrect method of connecting points.
(a) Correct (b) Incorrect
Figure 3-11 Correct and incorrect methods for showing and connecting data points on a graph.
R
INT
R
INT
- + (b) + -
(a)
1k Ω
R
INT
1.5k
(c)
+ -
2.2k
Ω
Figure 3-12 Test circuit for Section D
Section D:
1. Construct the circuit shown in Figure 3-12. Use three 1.5 volt cells and 3 different resistor values,
1 k Ω , 1.5k
Ω , and 2.2k
Ω for the three internal resistances (R int
).
2. Using the voltage notation, E ba
, etc., as described in the theory portion of this exercise, measure the following voltages: E ba
, E bc
, and E ac
. Check the voltage range setting of the voltmeter and remember that the meter is to be placed in parallel with the circuit being tested.
3. If the meter and circuit were set up correctly, all measurements caused the meter to read positive.
4. Using the voltmeter and the circuit of Step 1, Figure 3-12, measure the voltage across the following points: E ab
, E cb
and E ca
. If the voltage notations are interpreted properly, the meter will read negative. Since there are no scale divisions on the analog meter in the down-scale direction, the meter leads must be reversed so the meter deflects up scale. To indicate the meter originally deflected down scale, a negative sign is placed in front of the voltage reading.
5. Write your summary of experiment three and include it in your written report.

Basic D.C. AVIM 121 Lab 3 Page 5 of 8
Name:
Date:
Section A: Voltage Measurement
6.
Section B: Aiding and Opposing Voltage Sources
1. 2. 3.
4. 5.
Section C: Internal Resistance
1.
6.
R
INT
(ohms)
Elapsed Time
(hours)
V
0
(volts)
R
INT
(ohms)
4.7
Ω 1.0 2.2k
Ω
2.7k
Ω 10 Ω 2.0
100 Ω 3.0
470 Ω 4.0
1k Ω 4.5
1.5k
Ω 5.0
Section D: Voltage Notation
2. E ba
E bc
E cb
4. E ab
3.9k
Ω
4.7k
Ω
5.6k
Ω
6.8k
Ω
E ac
E ca
Elapsed Time
(hours)
5.5
6.0
6.5
7.0
7.5
8.0 rev. 08.09
V
0
(volts)

Basic D.C. AVIM 121 Lab 3
Page 6 of 8 rev. 08.09

Basic D.C. AVIM 121 Lab 3 Page 7 of 8 rev. 08.09
Linear Graph Paper

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Basic D.C. AVIM 121 Lab 3 Page 8 of 8 rev. 08.09