Meters
5 February 2004
Analog and Digital Meters
Devices and Measurements
Objective
• At the conclusion of this presentation the student will describe
and identify:
– Safety precautions when using test equipment
– Analog Multimeters
– Digital Multimeters
– How to connect a voltmeter to a circuit to measure voltage
– How to connect an ammeter to a circuit to measure current
– How to connect an ohmmeter to measure resistance
• The student will be able to:
– Read voltage from an analog voltmeter
– Read current from an analog ammeter
– Read resistance from an analog ohmmeter
5 February 2004
Professor Andrew H. Andersen
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1
Meters
5 February 2004
Basic Circuit Measurements
• A voltmeter measures voltage across (in parallel) a
resistance or load
• An ammeter is inserted in the current path (in series) to
measure current
• Resistance is measured across a resistor, out-of-circuit,
with an ohmmeter
• Digital Multimeters (DMM’s) measure voltage, current
and resistance
5 February 2004
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Electrical Test Equipment - The Multimeter
• A multimeter is used to measure voltage, current or
resistance, depending upon the function selected
– A voltmeter is used to measure voltage across a
component or circuit
– An ammeter is used to measure current through a
circuit
– An ohmmeter is used to measure resistance
5 February 2004
Professor Andrew H. Andersen
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Meters
5 February 2004
Typical d’Arsonval Meter Movement
5 February 2004
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Meter Deflection is Proportional to Current
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Professor Andrew H. Andersen
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5 February 2004
A Typical Seven Segment Display
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Examples of Meter Displays and Symbols
Each of the above may be used to represent either an
ammeter (A), a voltmeter (V), or an ohmmeter (Ω)
5 February 2004
Professor Andrew H. Andersen
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4
Meters
5 February 2004
Typical Portable Multimeters
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Example of a Digital and Analog Multimeter
5 February 2004
Professor Andrew H. Andersen
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Meters
5 February 2004
Typical Digital Multimeters (DMM)
5 February 2004
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A Typical Analog Multimeter
5 February 2004
Professor Andrew H. Andersen
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Selecting the Proper Range on an Analog Meter
Select a range for maximum deflection of the pointer
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Measuring a Resistor
Remove power if
necessary and isolate
the component from
the circuit under test
5 February 2004
Professor Andrew H. Andersen
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7
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5 February 2004
Schematic Symbols for Meters
The analog voltmeter and ammeter must be connected to the
circuit with proper polarity to avoid damaging the meter
movement
The ohmmeter may only be used on unenergized components
5 February 2004
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Voltage Measurements
• To measure voltage, the voltmeter is placed in parallel across
the component; that is, one lead is place on each side of the
component
• Set an analog ammeter to the highest range when measuring an
unknown voltage
• Then switch to the next lowest rage until maximum deflection
of the pointer is obtained while remaining on the scale
5 February 2004
Professor Andrew H. Andersen
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Meters
5 February 2004
A Voltmeter Connected to Measure Voltage
5 February 2004
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Current Measurements
• To measure current, the ammeter must be placed in series with
the component; that is, it must be in line with the current path
• Usually, power is removed from the circuit before connecting
or removing the ammeter
• Set an analog ammeter to the highest range when measuring an
unknown current
• Then switch to the next lowest rage until maximum deflection
of the pointer is obtained while remaining on the scale
5 February 2004
Professor Andrew H. Andersen
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Meters
5 February 2004
An Ammeter Connected to Measure Current
5 February 2004
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Resistance Measurements
• To measure resistance
– If necessary circuit power must be removed
– Usually at least one lead of the component must be
removed from the circuit
– the ohmmeter is connected across a component
5 February 2004
Professor Andrew H. Andersen
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Meters
5 February 2004
Ohmmeter Connection to Measure Resistance
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Reading the Analog Meter
Professor Andrew H. Andersen
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Meters
5 February 2004
Example 1
Assume that the VOM shown is on the AC/DC 6 V scale. What is
the reading?
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Example 1 Solution
Assume that the VOM shown is on the AC/DC 6 V scale. What is
the reading?
Note that the reading is made on the 60
V scale and the user places the decimal.
4.5 V
MS
OH
50
50
10
5
0
A
DC C
AM A C
PS 0
dB
0
m 0
0
20
2
10
1
4
2
0
2
4
6
1
25
50 0
10
25
10
5
8
10
S
11 d
B
0 C
30 0 A C
6 D
12 AC PS
M
30 A
12
6
0
20
8
4
10
4
2
2
OH
M
2
200
40
8
0
1k
3
150
30
6
100
20
4
20
4
5
10
m
ANALOG MULTIMETER
5 February 2004
Professor Andrew H. Andersen
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5 February 2004
Example 2
Assume that the VOM shown is on the AC AMPS 3 A scale. What
is the reading?
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Example 2 Solution
Assume that the VOM shown is on the AC AMPS 3 A scale. What
is the reading?
Note that the reading is made on the 30 A AC
1.25 A
scale and the user places the decimal place.
MS
OH
50
50
10
0
20
2
10
20
8
4
10
4
2
2
5
A
DC C
AM A C
PS 0
dB
0
m 0
0
1
4
2
0
2
4
6
OH
M
2
1
200
40
8
25
10
5
8
10
S
25
50 0
10
11 d
B
0 C
30 0 A C
6 D
12 AC PS
M
30 A
12
6
0
3
150
30
6
100
20
4
0
1k
4
5
10
20
m
ANALOG MULTIMETER
5 February 2004
Professor Andrew H. Andersen
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5 February 2004
Example 3
When you change resistance scales on a VOM, what must first be
done before measuring a resistor?
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Example 3 Solution
When you change resistance scales on a VOM, what must first be
done before measuring a resistor?
Zero the meter by shorting the leads together and adjusting the
Zero Adjust control.
5 February 2004
Professor Andrew H. Andersen
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5 February 2004
Example 4
Assume that the VOM shown is on the Ω x100 scale. What is the
reading?
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Problem 4 Solution
Assume that the VOM shown is on the Ω x100 scale. What is the
reading?
5 February 2004
Professor Andrew H. Andersen
340Ω
Note that the reading is made on the Ω scale
and the user multiplies the reading by 100.
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