ECE 2100
Circuit Analysis
Lesson 6
Chapter 2: Design of a
Voltmeter and Ammeter using Analog Meters
Daniel M. Litynski, Ph.D.
http://homepages.wmich.edu/~dlitynsk/

ECE 2100
Circuit Analysis
Review Lesson 5
Chapter 2
Series Resistors and Voltage Division
Parallel Resistors and Current Division

ECE 2100
Circuit Analysis
Lesson 6
Chapter 2: Design of a
Voltmeter and Ammeter using Analog Meters

Lesson 6
Design of a Voltmeter and Ammeter using Analog Meters
Potentiometer

• Series: Two or more elements are in series if they are cascaded or connected sequentially and consequently carry the same current.
• The equivalent resistance of any number of resistors connected in a series is the sum of the individual resistances.
N
R eq
R
1
R
2
R
N
R n n 1
• The voltage divider can be expressed as v n
R
1
R
2
R n
R
N v
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• Potentiometer is an adjustable, three terminal, voltage divider device.
• The equivalent resistance of two variable resistors connected in a series is the sum of the individual resistances.
R ac
R ab
R bc
• Then the voltage out is governed by:
V out
V bc
R bc
R ac
V in
8

• The d’Arsonval movement measures current.
• The amount of current through its coil determines the amount of movement, or deflection, of a pointer .
• The movement consists of a moveable iron core coil mounted on a pivot between the poles of a permanent magnet. (See
Fig. 2.8)
• It is used with series or parallel resistors to make a voltmeter or ammeter respectively.
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• The Voltmeter measures voltage ACROSS an element.
– A Voltmeter is placed in parallel with the element to be measured.
– To construct a Voltmeter, put resistors in series with a d’Arsonval meter.
• The Ammeter measures current THROUGH an element.
– An Ammeter is placed in series with the element to be measured.
– To construct an Ammeter, put resistors in parallel with a d’Arsonval meter.
11

• Resistance Measure Method 1: Connect an ammeter and voltmeter in series and parallel respectively to the device. Assume linearity and use Ohm’s law to determine.
This is an indirect measurement.
• Resistance Measure Method 2: Connect an ohmmeter to the device. This is a direct measurement.
• To Build an Ohmmeter, use a d’Arsonval, a variable resistor, and a battery.
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ECE 2100
Circuit Analysis
Lesson 6
Chapter 2: Design of a
Voltmeter and Ammeter using Analog Meters