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Laboratory 1 & 2 Combined: An Introduction to the Digital Multimeter
EE-1301: Modern Electronic Technology
Read the discussion about digital multimeters on the following pages, then answer the following
questions?
1. Record the name and model number of your multimeter?
2. List seven types of measurements that can be taken using your multimeter? (see p. 7)
3. Briefly explain how measuring probes or test leads are used? Your answer should include how
to connect the leads to the multimeter and how to connect them to the object being measured!
(see p. 8)
4. In your own words, describe an “overrange” condition? Your answer should include how you
recognize “overrange” on the display? (see p. 8)
5. Briefly explain how one chooses the proper range for an electrical measurement? (see page 89)
Hand in only the first six page! Keep the rest of the pages in your course pack for future
reference.
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Laboratory 1 & 2 Combined: An introduction to the digital multimeter.
Measuring battery voltages:
6. Set your multimeter to the 20 volt DC voltage range. With the V lead on the “+” terminal
and the COM lead on the “-” terminal, measure the voltage of two AA-size zinc-carbon dry
batteries, and record the values (including units) below?
_____________
1st battery
_____________
2nd battery
7. Arrange your batteries into a series connection as shown at the right,
and measure the series voltage? _________ The series voltage should be
the sum of the individual voltages. Is your measured value roughly the
sum of the individual battery voltages?
8. Arrange your batteries into a parallel connection as
shown at the right, and measure the parallel voltage?
__________ (You may have to use short pieces of wire,
coins, or keys to form the parallel connection.) The parallel
voltage should be the same as the individual voltages. Is
your measured value roughly the same as the individual
battery voltage?
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Laboratory 1 & 2 Combined: An introduction to the digital multimeter.
9. Measuring known resistance values: Use a multimeter to measure the resistances of the
following known resistor elements. Always set the range to the lowest value that does not give
an OVERRANGE in the display! This gives the greatest accuracy in the reading.
Terminals
Value
(listed)
Value
(in ohms)
Measured Value
(include units)
Multimeter
Range (units)
#71 and #72
100
100 ohms
_______________
_____
#73 and #74
470
470 ohms
_______________
_____
#75 and #76
1K
1,000 ohms
_______________
_____
#77 and #78
2.2K
2,200 ohms
_______________
_____
#79 and #80
4.7K
4,700 ohms
_______________
_____
#81 and #82
10K
10,000 ohms
_______________
_____
#83 and #84
10K
10,000 ohms
_______________
_____
#85 and #86
22K
22,000 ohms
_______________
_____
#87 and #88
47K
47,000 ohms
_______________
_____
#89 and #90
100K
100,000 ohms
_______________
_____
#91 and #92
220K
220,000 ohms
_______________
_____
#93 and #94
470K
470,000 ohms
_______________
_____
10. Body resistance: Set your multimeter to the 2M or 20M range. Tightly grasp the red probe
tip in one hand and the black probe tip in the other. (This is safe.)
With dry hands, what is your resistance from hand to hand? _______________________
What is your resistance with wet hands? __________________
Do you feel anything?____________
Note: You should not feel any electrical effect in this measurement. The current in the
ohmmeter is a few millionths of an ampere, whereas the “threshold for sensing”--the smallest
current you can feel--is about one thousandth of an ampere. That is, the ohmmeter current is
about one thousandth of what you can feel, so you do not feel it.
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Laboratory 1 & 2 Combined: An introduction to the digital multimeter.
11. Revisiting the selection of range: The Science-Fair 130-in-one Electronic Project Labs have
two sets of batteries. Each set consists of three 1.5 volt AA-size carbon-zinc dry batteries
connected in series to produce a nominal voltage of 4.5 volts DC. With the red lead on the
terminal for the first number and the black lead on the terminal for the second number, measure
the following terminal voltage on different ranges and record the values (including units) below?
V119,121 = __________
1K Range
V119,121 = __________
200 V Range
V119,121 = __________
20 V Range
V119,121 = __________
2 V Range
V119,121 = __________
200mV (equal to 0.2 V) Range
Circle the readings that are overrange, and mark the lowest range that does not go overrange? As
previously stated in the discussion about selecting range, the most accurate reading--that is, the
reading with the most significant figures--occurs on the lowest range that does not go overrange.
The use of higher ranges to read a selected quantity is not incorrect; but the answer is not as
accurate as an answer from a lower scale that does not go overrange.
12. Continuity: The continuity test is a simple test to check for the presence of an electrical
connection between two points. Set your multimeter range switch on the continuity test, place
the test probes in the COM and V connections, and touch the test leads together. You should
hear an audible buzzing sound which indicates a continuous connection between the test leads.
Ask the TA for help if you are unable to hear the buzzer.
Attach the alligator clips on the test leads to terminals #137 and #138 (the key switch).
What happens when the key switch is depressed?
Attach the alligator clips to terminals #134 and #135 on the slide switch. What can you
say about continuity when the switch is in position A?
What about position B?
Is there continuity between terminals #134 and #136 in either position?
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Laboratory 1 & 2 Combined: An introduction to the digital multimeter.
Slide switch discussion: Terminal #135 is considered to be a common terminal relative
to terminals #134 and #136. Continuity between #135 and #134 or between #135 and #133
depends on the switch position. The same can be said for terminal #132 relative to terminals
#131 and #133. Because the switch has two common terminals and two switch positions, it is
called a “double-pole, double-throw” (abbreviated DPDT) switch.
13. Diode test: Diodes are semiconductor devices that only allow current to pass in one
direction. In previous tests, the resistance measurements did not depend on how the test leads are
connected to the device under test; but when you test a diode, there is a polarity difference.
If the diode is good, you should obtain a valid resistance reading in one direction (the
forward conducting direction); and in the other direction (the reverse non-conduction
direction), you should show an over-range indication.
If the diode is bad, both readings are the same--either a valid reading or an over-range
indication.
Set your multimeter range switch on the diode test range and perform the following diode tests?
In the diode test, do not change ranges when the display shows the OVERRANGE. Be sure to
indicate if each device is good or bad!
Germanium diodes: Diode test125, 126 = _______
Diode test126, 125 = ________
Good/Bad
Silicon diode:
Diode test129, 130 = _______
Diode test130, 129 = ________
Good/Bad
LEDs:
Diode test31, 32 = _______
Diode test32, 31 = ________
Good/Bad
Diode discussion:
The silicon diodes have less reverse-bias leakage than germanium diodes, but germanium diodes
have a lower forward conduction voltage than silicon diodes, as shown by the lower value of the
forward-bias diode test value. Both silicon and germanium devices should show over-range in
the reverse direction.
The LEDs (light-emitting diodes) also have a forward/reverse conduction characteristic.
In reverse bias, the LEDs should exhibit an over-range indication; but in forward bias, there
should be a proper reading. In an LED in forward bias, the recombination of current carriers in
the GaAs (gallium arsenide) substrate produces visible red light. Performing the diode test
should result in visible light when you test the LED in the forward direction. The recombination
of carriers in forward bias in silicon and germanium diodes also produces light, but the emitted
light is in the invisible infra-red part of the electromagnetic spectrum.
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Laboratory 1 & 2 Combined: An introduction to the digital multimeter.
14. In your own words, briefly state the purpose of this laboratory exercise?
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Laboratory 1 & 2 Combined: An introduction to the digital multimeter.
Laboratory 1 & 2 Combined Discussion: Digital Multimeters
There are many manufacturers of digital multimeters, and there are at least three brands
available for use in the EE-1301 laboratory. All three of them provide the user with generally the
same capability. This “introduction” is an outline of how to use these multimeters to make
electrical measurements.
As the name “multimeter” implies, the instrument provides the user with the capability to
measure multiple electrical properties. Properties such as electrical pressure or voltage
(measured in volts), the flow of electric current (measured in amperes), and the resistance to flow
(measured in ohms) can all be measured with the same instrument. The adjective “digital” refers
to the number format of the measured electrical information as it is presented to the user. An
“analog” multimeter uses the deflection of a needle to indicate the magnitude of the quantity
being measured.
Digital multimeters have the following common features:
An “on/off” switch.
An internal battery or other power source.
A “common” input terminal.
A “volt & ohm” input terminal, usually written as V .
An “ampere” input terminal.
A “milliampere” input terminal.
A “selector” button mechanism or rotary switch (or both) to choose which property to
measure and the proper range.
A “digital display” panel which includes a “polarity” indicator and an “overload” indicator.
A set of leads to connect the multimeter to the circuit.
Seven types of measurements:
AC and DC volts from 200 millivolts full scale to 1000 volts full scale.
AC and DC current from 200 microamperes to 10 amperes full scale.
DC resistance from 200 ohms to 20 megohms full scale.
The continuity buzzer is useful for testing for the presence of an electrical connection
(continuity) between the test leads.
The diode test is useful for checking the forward and reverse characteristics of PN
junction diodes, LEDs, and transistors.
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Laboratory 1 & 2 Combined: An introduction to the digital multimeter.
Connecting the test leads:
Voltage: The meter measures the voltage difference (or electrical pressure difference)
between the voltage at the “V " input and the voltage at the “COM” input. Generally, the red
lead is inserted into the “V " input and the black lead into the “COM” input, although the color
convention can be reversed if desired. Testing a battery with the “+” connected to the “V " lead
and the “-” connected to the “COM” lead will result in a positive reading. Reversing the battery
connections will produce a negative reading.
Resistance: The meter measures resistance by imposing a small voltage between the
“V " input and the “COM” input. By measuring the current that flows when an unknown
resistance is connected to the test leads, the meter determines the unknown resistance value.
Generally, the red lead is inserted into the “V " input and the black lead into the “COM” input,
although the color convention can be reversed if desired. Reversing the connections while
measuring resistance gives the same result unless you are testing a diode or a transistor.
Current: The meter measures the current flowing into the A or
mA input. The red lead is generally plugged into either the “A” input
or the “mA” input, while the black lead is plugged into the “COM”
input. To measure current in a particular lead or wire, the wire must
be disconnected, and the meter leads are connected to the
disconnected lead and the point of disconnection. In this way, the
unknown current is forced to flow through the meter. This type of
current measurement is called a direct measurement of current, as
opposed to an indirect measurement of current where the current is
calculated using Ohm’s Law from a voltage drop reading across a
known resistance. The drawing to the right shows an example of the
direct measurement of current flowing from terminal 77 to terminal
13.
Selecting the proper range:
For the greatest accuracy, one should always use the lowest range that does not give an
“overrange” indication. Using a higher range still gives a valid reading, but there is a reduction
in the number of significant figures in the answer.
The overrange indication:
If the quantity being measured is larger than the full-scale quantity, the reading will
display the overrange indication. For most of the meters in Modern Electronic Technology, the
overrange reading is simply a “one” followed by a “decimal” and “blanks” in each of the digit
locations. For example, a 1.5 volt AA battery read on the 200 mV range will give the
“overrange” indication. In another example, on any of the resistance ranges with the test leads
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Laboratory 1 & 2 Combined: An introduction to the digital multimeter.
not connected, the resistance between the test leads is effectively “infinity” which is larger than
any of the test ranges. Hence, unconnected leads in the ohmmeter test always produce the
“overrange” indicator.
Examples of voltage readings of a 1.5 volt AA battery on different scales.
DC Volts Range
1K
200
20
2
200m
Reading
002.
1.6
1.56
1.559
1.
Units
volts
volts
volts
volts
(overrange)
Examples of electrical quantities:
Voltage:
1,000,000 volts
50,000 volts
25,000 volts
120 volts
12 volts
3.7 volts
3.3 volts
2.0 volts
1.5 volts
1.2 volts
0.001 volts
0.000001 volts
Current:
600 amps
6 amps
0.83 amp
0.040 amp
0.000001 amp
Resistance:
100,000,000 ohms
470,000 ohms
50,000 ohms
470 ohms
144 ohms
60 ohms
6 ohms
0.000001 ohms
1 MV
50 KV
25 KV
1 mV
1 V
AC
AC
DC
AC
DC
DC
DC
DC
DC
DC
AC
AC
Power transmission lines
Primary distribution lines
Voltage on TV picture tube
Household voltage (60 Hz)
Automotive voltage
Voltage from lithium-polymer battery
Voltage from lithium 123 battery
Voltage from lead-acid wet cell
Voltage from carbon-zinc battery
Voltage from nickel-cadmium battery
Voltage from tape-deck pickup
Voltage at radio receiver antenna
40 mA
1 A
DC
DC
AC
DC
DC
Current in car starter
Current in car headlight
Current in 100 watt light bulb
Current in portable AM/FM receiver battery
Current in quartz watch battery
DC
DC
DC
DC
AC
DC
DC
DC
Resistance of reverse-biased diode
Largest resistance in lab kit
Resistance of control (R26, 28) in lab kit
Moderate resistance in lab kit
Resistance of lighted 100 watt light bulb
Resistance of transformer (R3,5) in lab kit
Resistance of radio coils in lab kit
Resistance of 1 cm cube of metal
100 M
470 K
1
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Laboratory 1 & 2 Combined: An introduction to the digital multimeter.
On resistors and resistance.
The first time I ever studied (a euphemism for torn up or destroyed) the inside of a radio
(at about age 9), I asked my dad the name of some of the parts found inside. He didn’t know so
he referred me to a local radio-TV repair shop. There, a friendly technician told me that some of
the elements were resistors.
"What do the resistors do?", I asked. (Probably one of a thousand questions that I
pestered him with that day. He got even with me a few years later, but how he did will have to
wait for our study of television.)
The technician patiently answered, "the resistors hold back the flow of electricity."
And I replied, with all the logic of a nine year old, "wouldn't this radio have worked better
if the electricity wasn't held back?"
That was a good comment, and the best way to think about the role of resistors in circuits
is that they behave somewhat like the throttle in your automobile--you don't always want to go
full speed ahead.
**********
Notes on batteries:
A battery consists of two different electrodes in contact with a liquid, paste, or gel
electrolyte. The electrolyte chemically reacts with the electrodes to produce a voltage difference
between the two electrodes. If the battery is connected into a circuit, the voltage produced by the
chemical reaction results in the flow of current. The magnitude of the current can be calculated
using Ohm’s Law. As current is produced, one electrode is gradually consumed. Gasses may
also be given off as the electrodes react with the electrolyte.
All batteries deliver DC (direct current). I am not aware of any battery that delivers AC
by itself, although there are methods for converting the DC to AC.
Your standard AAA, AA, C, or D battery is a zinc-carbon dry cell, and it delivers about
1.5 volts DC. The zinc-carbon refers to the materials that make up the electrodes of the battery.
Zinc-carbon batteries are not rechargeable.
Alkaline batteries are similar to zinc-carbon batteries in composition of the electrodes and
the output voltage, but a different electrolyte gives a lower internal resistance and a greater
output current. Alkaline batteries are not rechargeable.
Silver oxide and lithium batteries are also examples of dry batteries that are not
rechargeable.
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Laboratory 1 & 2 Combined: An introduction to the digital multimeter.
Nickel-cadmium or nickel-metal-hydride batteries deliver about 1.2 volts per cell, and
they are rechargeable.
Lead-acid batteries also are rechargeable, and they deliver about 2.0 volts per cell.
An automobile battery is made up of six lead-acid cells connected in series for a nominal
12 volt battery.
Lithium 123 batteries deliver about 3.3 volts per cell, and they are rechargeable.
Lithium polymer batteries deliver about 3.7 volts per cell, and they are rechargeable.
Fresh batteries generally produce a voltage from 0.1 to 0.2 volts greater than the nominal
voltage for that battery type. As the stored energy is depleted, the voltage gradually falls and
internal resistance increases until there is insufficient voltage at the terminals to operate the
intended application. At that time, dry batteries must be replaced, or rechargeable batteries must
be charged.
Series and Parallel
Your multimeter can be used to measure (or check) the voltage of a battery. Set your
multimeter to read DC volts on the 20 volt scale. To measure the voltage of a single AA battery
as shown to the left below, connect the V lead to the “+” terminal and the COM to the “-”
terminal.
Single battery.
Batteries in series.
Batteries in parallel.
The voltage of batteries in series is the sum of the individual voltages! Series
combinations of batteries are used when a larger voltage is needed. The middle drawing shows
the multimeter measuring the voltage of batteries in series. The voltage of identical batteries
connected in parallel is the same as the individual batteries! Parallel combinations of batteries are
needed when additional current capacity (or longer battery life) is needed. The right-hand
drawing shows the voltage measurement of batteries in parallel.
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Laboratory 1 & 2 Combined: An introduction to the digital multimeter.
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