Meters 23 July 2005 Professor Andrew H. Andersen 1 ELEC 103 Analog and Digital Meters Devices and Measurements 23 July 2005 Meters 2 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
Transcript
Meters 23 July 2005
Professor Andrew H. Andersen 1
ELEC 103
Analog and Digital Meters Devices and Measurements
23 July 2005 Meters 2
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
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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 with the same connections as the analog meter
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Electrical Test Equipment - The Multimeter• A multimeter is a single piece of text equipment that may be
used to measure voltage, current or resistance, depending upon the function selected– Analog mulitmeters have both range and function switches– Digital multimeters are usually autoranging– 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
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Typical d’Arsonval Meter Movement
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Meter Deflection is Proportional to Current
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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)
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Typical Portable Multimeters
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Example of a Digital and Analog Multimeter
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Typical Digital Multimeters (DMM)
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A Typical Analog Multimeter
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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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A Simpson 260 Analog Multimeter
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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
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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 voltmeter 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
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A Voltmeter Connected to Measure Voltage
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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
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An Ammeter Connected to Measure Current
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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
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Ohmmeter Connection to Measure Resistance
Reading the Analog Meter
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Example 1Assume that the VOM shown is on the AC/DC 6 V scale. What is the reading?
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00
0
ACDC
ACDC00
0
5010
25
21
100 20 4
10 4 2
150 30 6
200 40
820
8 4
250 50 102510 5
300 60 123012 6
ANALOG MULTIMETER
AC AMPS
dBm
dBm
OHMS
0
1
2345
10
20
20
50
OHMS
1k
A
C A
MPS 104
2 0 2 4 6 810
11
Example 1 Solution
Assume that the VOM shown is on the AC/DC 6 V scale. What is the reading?
4.5 V Note that the reading is made on the 60 V scale and the user places the decimal.
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Example 2Assume that the VOM shown is on the AC AMPS 3 A scale. What is the reading?
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00
0
ACDC
ACDC00
0
5010
25
21
100 20 4
10 4 2
150 30 6
200 40
820
8 4
250 50 102510 5
300 60 123012 6
ANALOG MULTIMETER
AC AMPS
dBm
dBm
OHMS
0
1
2345
10
20
20
50
OHMS
1k
A
C A
MPS 104
2 0 2 4 6 810
11
Example 2 SolutionAssume that the VOM shown is on the AC AMPS 3 A scale. What is the reading? 1.25 A Note that the reading is made on the 30 A AC
scale and the user places the decimal place.
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Example 3When you change resistance scales on a VOM, what must first be done before measuring a resistor?
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Example 3 SolutionWhen 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.
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Example 4Assume that the VOM shown is on the Ω x100 scale. What is the reading?
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Problem 4 SolutionAssume that the VOM shown is on the Ω x100 scale. What is the reading? 340Ω Note that the reading is made on the Ω scale
