Analog and Digital Meters - Brookdale Communityux.brookdalecc.edu/fac/engtech/andy/elec106/powerpoint/meters.pdf · Professor Andrew H. Andersen 1 Analog and Digital Meters Devices

Meters 5 February 2004

Professor Andrew H. Andersen 1

Analog and Digital Meters

Devices and Measurements

5 February 2004 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

Meters 5 February 2004

Professor Andrew H. Andersen 2

5 February 2004 Meters 3

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 Meters 4

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

Meters 5 February 2004

Professor Andrew H. Andersen 3

5 February 2004 Meters 5

Typical d’Arsonval Meter Movement

5 February 2004 Meters 6

Meter Deflection is Proportional to Current

Meters 5 February 2004

Professor Andrew H. Andersen 4

5 February 2004 Meters 7

A Typical Seven Segment Display

5 February 2004 Meters 8

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)

Meters 5 February 2004

Professor Andrew H. Andersen 5

5 February 2004 Meters 9

Typical Portable Multimeters

5 February 2004 Meters 10

Example of a Digital and Analog Multimeter

Meters 5 February 2004

Professor Andrew H. Andersen 6

5 February 2004 Meters 11

Typical Digital Multimeters (DMM)

5 February 2004 Meters 12

A Typical Analog Multimeter

Meters 5 February 2004

Professor Andrew H. Andersen 7

5 February 2004 Meters 13

Selecting the Proper Range on an Analog Meter

Select a range for maximum deflection of the pointer

5 February 2004 Meters 14

Measuring a Resistor

Remove power if necessary and isolate the component from the circuit under test

Meters 5 February 2004

Professor Andrew H. Andersen 8

5 February 2004 Meters 15

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 Meters 16

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

Meters 5 February 2004

Professor Andrew H. Andersen 9

5 February 2004 Meters 17

A Voltmeter Connected to Measure Voltage

5 February 2004 Meters 18

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

Meters 5 February 2004

Professor Andrew H. Andersen 10

5 February 2004 Meters 19

An Ammeter Connected to Measure Current

5 February 2004 Meters 20

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

Meters 5 February 2004

Professor Andrew H. Andersen 11

5 February 2004 Meters 21

Ohmmeter Connection to Measure Resistance

Reading the Analog Meter

Meters 5 February 2004

Professor Andrew H. Andersen 12

5 February 2004 Meters 23

Example 1Assume that the VOM shown is on the AC/DC 6 V scale. What is the reading?

5 February 2004 Meters 24

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.

Meters 5 February 2004

Professor Andrew H. Andersen 13

5 February 2004 Meters 25

Example 2Assume that the VOM shown is on the AC AMPS 3 A scale. What is the reading?

5 February 2004 Meters 26

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.

Meters 5 February 2004

Professor Andrew H. Andersen 14

5 February 2004 Meters 27

Example 3When you change resistance scales on a VOM, what must first be done before measuring a resistor?

5 February 2004 Meters 28

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.

Meters 5 February 2004

Professor Andrew H. Andersen 15

5 February 2004 Meters 29

Example 4Assume that the VOM shown is on the Ω x100 scale. What is the reading?

5 February 2004 Meters 30

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

and the user multiplies the reading by 100.