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Report Assignment BENP 2183 Electronic Instrumentations

1

REPORT ASSIGNMENT

1.0 TITLE

Design of basic shunt DC multirange ammeter using Permanent Magnet

Moving Coil (PMMC) of AI fsd µ100= for range of mAmA 1500,1000 −−

and mA300 .

2.0 OBJECTIVES

i. To design a basic shunt DC multirange ammeter using PMMC.

ii. To understand the properties of a basic shunt DC multirange ammeter.

iii. To calculate the current through a circuit measured by basic shunt DC

multirange ammeter using PMMC.

iv. To measure the actual value internal resistance of PMMC.

3.0 EQUIPMENTS/ MATERIALS

NO. EQUIPMENT UNIT/S

1 Resistor 2.2Ω 3

2 PMMC (micro-ammter) 1

3 4 ways switch 1

4.0 THEORY

Meter

A meter is any device built to accurately detect and display an electrical

quantity in a form readable by a human being. Usually this "readable form" is visual:

motion of a pointer on a scale, a series of lights arranged to form a "bar graph," or

some sort of display composed of numerical figures. In the analysis and testing of

circuits, there are meters designed to accurately measure the basic quantities of

voltage, current, and resistance. The display mechanism of a meter is often referred to

as a movement, borrowing from its mechanical nature to move a pointer along a scale

so that a measured value may be read.

The design of most mechanical movements is based on the principle of

electromagnetism: that electric current through a conductor produces a magnetic field

perpendicular to the axis of electron flow. The greater the electric current, the stronger


2

the magnetic field produced. If the magnetic field formed by the conductor is allowed

to interact with another magnetic field, a physical force will be generated between the

two sources of fields. If one of these sources is free to move with respect to the other,

it will do so as current is conducted through the wire, the motion which usually

against the resistance of a spring being proportional to strength of current.

However, practical electromagnetic meter movements can be made now where a

pivoting wire coil is suspended in a strong magnetic field, shielded from the majority

of outside influences. Such an instrument design is generally known as a permanent-

magnet, moving coil, or PMMC movement:

Figure 1: Construction of Permanent Magnet Moving Coil (PMMC)

In the picture above, the meter movement "needle" is shown pointing

somewhere around 35 percent of full-scale, zero being full to the left of the arc and

full-scale being completely to the right of the arc. An increase in measured current

will drive the needle to point further to the right and a decrease will cause the needle

to drop back down toward its resting point on the left. The arc on the meter display is

labeled with numbers to indicate the value of the quantity being measured, whatever

that quantity is.


3

Ammeter

Figure 2: A Typical 0-1mA Ammeter

Figure 3: D’Arsonval used in DC

Ammeter circuit

A meter designed to measure electrical current is popularly called an "ammeter"

because the unit of measurement is "amps." The earliest design is the D'Arsonval

galvanometer or moving coil ammeter. It uses magnetic deflection, where current

passing through a coil causes the coil to move in a magnetic field. The voltage drop

across the coil is kept to a minimum to minimize resistance across the ammeter in any

circuit into which it is inserted.

Besides that, moving iron ammeters use a piece or pieces of iron which move

when acted upon by the electromagnetic force of a fixed coil of wire. This type of

meter responds to both direct and alternating currents as opposed to the moving coil

ammeter, which works on direct current only

To measure larger currents, a resistor called a shunt is placed in parallel with the

meter. Most of the current flows through the shunt, and only a small fraction flow

through the meter. This allows the meter to measure large currents.

Multi-Range Ammeter

In practical terms, ammeters with a single range are not very useful. However

there are some exceptions such as Marine meters-voltage, fuel, Power station meters

(voltage, frequency) and automotive meters (ammeter, tachometer).All of which have

one useful range.

To make an ammeter to measure several ranges at once, one approach is to have

a separate shunt resistor for each range and we can calculate each resistor value of the

shunt.


4

Figure 4: Several Range Meter Connections

By referring to Figure 4, the position of the switch, one of R1 to R4 would be

connected as a shunt across the meter. However, a problem may have with thus

arrangement. At the point when the switch is moved from position 1 to position 2, the

PMMC movement will be forced to pass a current that may be more than full scale

deflection current, fsdI . This will most likely destroy the meter, or at best blow a fuse.

Hence, to solve of this problem another ways of connection can be used. Those are a

make-before-break switch and a Universal or Ayrton Shunt. The make-before-switch

establishes contact with the next contact position before losing contact with the

existing connection. In this manner, the shunt resistors are never removed from the

circuit and the PMMC movement is always protected.

Figure 5: The Make-Before-Switch Connection


5

Figure 6: The Universal or Ayrton shunt of Multi-Range Ammeter

As refer to Figure 5, the Universal or Ayrton shunt connection. The shunt

resistors, R1, R2 and R3, are all in series and collectively in parallel to the meter

movement. Thus,

321 RRRRsh ++=

If the input is connect to position 1, it can be say that

mmm

mmshsh

msh

RIRRRII

RIRI

VV

=++−

=

=

)321)((

Where, Ish = shunt current for this position.

If the input is connect to position 2,

)1()32)(( RRIRRII mmm +=+−

If the input is connect to position 3,

)21()3)(( RRRIRII mmm ++=−

Hence, by using substitution of equations the value of shunt resistors, R1, R2

and R3 can be calculated. Besides, this method is used for this project.

5.0 PROCEDURE

1. A basic shunt DC multirange ammeter was designed using PMMC of

Ifsd=100µA for range of 0-100mA, 0-150mA and 0-300mA.

2. The designed circuit was tested by using Multisim.

3. The internal resistance, Rm for the micro-ammeter was measured by using

DMM.


6

4. The designed circuit was constructed on a breadboard and the circuit was

checked.

5. The observation and the finding were discussed.

6.0 RESULT

Theoretical/ Calculation Result

To design basic shunt DC multirange ammeter using PMMC, the Aryton

Shunt or Universal Shunt was used.

AI fsd µ100=SHI

Figure 1: An Aryton Shunt design circuit

Calculation for circuit in Figure 1 to provide an ammeter with a current range

of mAmA 1500,1000 −− , mA3000 − and AI fsd µ100= .

Firstly, voltage across resistors R1, R2 and R3 parallel with the voltage Rm.

Hence,

MMSHSH

RmSH

RIRI

VV

=

=

But,

fsdSH

fsdSH

III

III

−=∴

+=

For range ,1000 mA−

RmRRRm µµ 100)123)(100100( =++−


7

RmRRRm µ100)123(9.99 =++ -- (1)


RmRRm µµ 100)12)(100150( =+−

)3(100)12(9.149 RRmRRm +=+ µ -- (2)

)3(11.667)12( RRmRR +=+ µ -- (3)


RmRm µµ 100)1)(100300( =−

)23(100)1(9.299 RRRmRm ++= µ

)23(44.3331 RRRmR ++= µ -- (4)

Substitute equation (3) into equation (1),

[ ][ ]

RmmR

RmRRmmRm

RmRRmRm

RmRRmRm

36.33397.99

100364.6664.669.99

100311.66711.66739.99

100)3(11.66739.99

=

=++

=++

=++

µµµ

µµµ

µµ

RmR µ70.3333 = -- (5)

Substitute equation (3) and equation (4) into equation (2),

[ ]

RmR

RmRmRmR

RRmRRRmR

RRmRRRmRm

µµ

µµµµµµ

µµµµ

µµ

82.333)44.3331(2

)7.333(11.667)7.333(44.33344.333)44.3331(2

)3(11.667244.333344.33344.3332

)3(100)23(44.33329.149

=+

=+++

+=+++

+=+++

RmR µ71.3332 = -- (6)

Substitute equation (5) and equation (6) into equation (4),

Rm

nRmnRmRm

RmRmRm

RRRmR

µ

µ

µµµ

µ

66.333

27.11127.11144.333

)71.33370.333(44.333

)23(44.3331

=

++=

++=

++=

Hence, the value of R3, R2 and R1

RmR

RmR

RmR

µ

µ

µ

66.3331

71.3332

70.3333

=

=

=∴

From the laboratory result, the Rm for the PMMC micro-ammeter is 6.72kΩΩΩΩ

Therefore, the value of R3, R2 and R1


8

Simulation Result

(i) A basic DC circuit of voltage source and resistor was constructed and

measure by using multimeter in Multisim Software.

Figure 2

Calculation by using mathematical method:

By using Ohm’s Law,

)(12

1

12

provedmA

k

R

VI

IRV

calculated

=

=

=

=


9

(ii) A designed basic shunt DC Multirange ammeter and connected to a

basic circuit as in Figure 1 was constructed by using Multisim Software.

Figure 3

(iii) Internal resistance of ammeter was set to 6.72k Ω .

Figure 4


10

Due to set value of internal resistance, Rm=6.72k Ω hence the resistor’s value

obtained and used in designed basic shunt DC Multirange ammeter was,

Ω=

=

=

Ω=

=

=

Ω=

=

=

242.2

)72.6(66.333

66.3331

242.2

)72.6(71.333

71.3332

242.2

)72.6(70.333

70.3333

k

RmR

k

RmR

k

RmR

µ

µ

µ

µ

µ

µ

(iv) A basic DC circuit was measured by using designed basic shunt DC

Multirange ammeter of AI fsd µ100= for range of mA1000 − .

Range of mA1000 − on designed ammeter was selected to measure the current of DC

circuit as connected.

Measured current value from ammeter, AI µ001.12= .


11

Hence,

rangeselected

fsd

measured

circuitdc II

II ×=

Given, AI fsd µ100=

mI circuitdc 100100

00.12×=∴

µ

µ

calculatedI

mA

=

= 00.12

(v) A basic DC circuit was measured again by using designed basic shunt DC

Multirange ammeter of AI fsd µ100= for range of mA1500 − .

Range of mA1500 − on designed ammeter was selected to measure the current of DC



Hence,

mI circuitdc 150100

815.7×=∴

µ

µ

calculatedImA

mA

≈≈

=

0.12

7225.11


12

(v) A basic DC circuit was measured again by using designed basic shunt DC

Multirange ammeter of AI fsd µ100= for range of mA300 .

Range of mA300 on designed ammeter was selected to measure the current of DC



Hence,

mI circuitdc 300100

916.3×=∴

µ

µ

calculatedImA

mA

≈≈

=

0.12

748.11

Laboratory Result

The internal resistance, Rm for the PMMC micro-ammeter is 6.72kΩΩΩΩ

ComponentsComponentsComponentsComponents Measured valueMeasured valueMeasured valueMeasured value

Internal resistance, Rm 6.72kΩ

Resistor 1kΩ 0.989kΩ


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Resistor 2.2Ω 2.2Ω

SHm

SH

fsdmRR

IRII

+==

µ12.98

6.672.6

)6.6)(100(

=

+=

k

m

The range 0 The range 0 The range 0 The range 0 –––– 100mA 100mA 100mA 100mA

VoltageVoltageVoltageVoltage,Vin,Vin,Vin,Vin

(V)(V)(V)(V)

Measured Measured Measured Measured current,Icurrent,Icurrent,Icurrent,I

((((µµµµAAAA))))

Calculated valueCalculated valueCalculated valueCalculated value,Vo,Vo,Vo,Vo

((((VVVV))))

% error % error % error % error

(%)(%)(%)(%)

10 10 10.08 0.80

11 11 11.09 0.81

12 12 12.10 0.83

13 13 13.10 0.76

14 14 14.11 0.79

15 15 15.12 0.80

16 16 16.13 0.81

17 17 17.13 0.76

18 18 18.14 0.78

19 19 19.15 0.79

20 20 20.16 0.80


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The range 0 The range 0 The range 0 The range 0 –––– 1 1 1 155550mA0mA0mA0mA

VoltageVoltageVoltageVoltage,Vin ,Vin ,Vin ,Vin

(V)(V)(V)(V)

MeasurMeasurMeasurMeasured current,I ed current,I ed current,I ed current,I

((((µµµµA)A)A)A)

Calculated value,Vo Calculated value,Vo Calculated value,Vo Calculated value,Vo

(V)(V)(V)(V)


(%)(%)(%)(%)

10 7.0 10.58 5.8

11 7.6 11.49 4.45

12 8.0 12.10 0.83

13 9.0 13.61 4.69

14 9.0 13.61 2.78

15 10.0 15.12 0.80

16 11.0 16.63 3.94

17 11.4 17.24 1.41

18 12.0 18.14 0.78

19 13.0 19.65 3.42

20 13.6 20.56 2.80

The range 0 The range 0 The range 0 The range 0 –––– 300300300300mAmAmAmA

VoltageVoltageVoltageVoltage,Vin ,Vin ,Vin ,Vin

(V)(V)(V)(V)

Measured current,I Measured current,I Measured current,I Measured current,I

((((µµµµA)A)A)A)

Calculated value,Vo Calculated value,Vo Calculated value,Vo Calculated value,Vo

(V)(V)(V)(V)


(%)(%)(%)(%)

10 3.6 10.88 8.80

11 4.0 12.09 9.91

12 4.0 12.09 0.75

13 4.4 13.3 2.31


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14 5.0 15.12 8.0

15 5.2 15.72 4.80

16 5.6 16.93 5.81

17 6.0 18.14 6.71

18 6.0 18.14 0.78

19 6.4 19.35 1.84

20 7.0 21.17 5.85

ForForForFor range 0 range 0 range 0 range 0 –––– 100mA 100mA 100mA 100mA

The calculation of the Vo,

When Vin = 10V

4)( xRrangexI

IVo

fsd

=

V

kxmAx

08.10

989.0)100(12.98

10

=

=µ

µ

When Vin = 11V

11.09V

.989kx(100mA)x012.98

11

=

=µ

µVo

The calculation of the percentage error,

When Vin = 10V,


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%100||% xYn

XnYnerror

−=

%8.0

%100|10

08.1010|

=

−= x

When Vin = 11V,

%100|11

09.1111|% xerror

−=

%81.0=

ForForForFor range 0 range 0 range 0 range 0 –––– 1 1 1 155550mA0mA0mA0mA


When Vin = 10V

4)( xRrangexI

IVo

fsd

=

V

kxmAx

58.10

989.0)150(12.98

7

=

=µ

µ

When Vin = 11V

11.49V

.989kx(150mA)x012.98

6.7

=

=µ

µVo



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When Vin = 10V,

%100||% xYn

XnYnerror

−=

%8.5

%100|10

58.1010|

=

−= x

When Vin = 11V,

%100|11

49.1111|% xerror

−=

%45.4=

ForForForFor range 0 range 0 range 0 range 0 –––– 303030300mA0mA0mA0mA


When Vin = 10V

4)( xRrangexI

IVo

fsd

=

V

kxmAx

88.10

989.0)300(12.98

6.3

=

=µ

µ

When Vin = 11V

12.09V

.989kx(300mA)x012.98

0.4

=

=µ

µVo



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When Vin = 10V,

%100||% xYn

XnYnerror

−=

%80.8

%100|10

88.1010|

=

−= x

When Vin = 11V,

%100|11

09.1211|% xerror

−=

%91.9=


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7.0 DISCUSSION/ ANALYSIS

The shunt resistance was very small relative to the internal resistance of the

micro-ammeter. A high voltage that passes through the shunt resistor may cause the

resistor burnt. Therefore, no connection was made from the resistors directly to the

high voltage supply. A resistor which has a high resistance is connected to the shunt

resistor in parallel to avoid the burning of resistors occur.

A Permanent Magnet Moving Coil (PMMC) was used to design an ammeter,.

Before design the ammeter, internal resistance of the PMMC was measured to do the

calculation. The PMMC galvanometer constitutes the basic movement of a dc

ammeter. Since the coil winding of a basic movement is small and light, it can carry

only very small currents. When large currents are to be measured, it is necessary to

bypass a major part of the current through a resistance called a shunt.

The shunt resistance used may consist of a length of constant temperature

resistance wire within the case of instrument. The general requirements of a shunt are

as follows.

a. The temperature coefficient of the shunt and instrument should be low

and nearly identical.

b. The resistance of the shunt should not vary with time.

c. It should carry the current without excessive temperature rise.

d. It should have a low thermal emf.

The current range of the dc ammeter may be further extended by a number of

shunt and it is known as multirange ammeter. A switch can be connected in the circuit

to choose the range desired. The switch used to connect in the circuit must be a low

resistance and high current carrying capacity, since its contacts are in series with low

resistance. To prevent the ammeter broken when in use, the highest current range was

used to measure current first, then decrease the range until good upscale reading is

obtained.

When an ammeter was inserted in a circuit, it always increases the resistance

of the circuit and reduces the current in the circuit. This effect was known as the

ammeter insertion effects. To reduce the insertion effects, the resistance used to

design the ammeter should be as low as possible.

8.0 CONCLUSION


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After doing this assignment, it is found that the ammeter was design by using

a PMMC. Beside that, to measured a large current, the ammeter can be designed with

a resistor connect parallel with the PMMC or known as shunt. In this assignment, a

basic shunt DC multirange ammeter using PMMC was designed.

Beside that, before design the ammeter, internal resistance of the PMMC was

measured first. When designing the multirange ammeter, some requirements as shown

in the discussion were considered, this is to make sure the ammeter that had designed

have an accurate and a precise reading.

The insertion effects which the ammeter will increases the resistance of the

circuit when connected in the circuit thus decreases the current flow in the circuit also

considered in the design. That is the resistor used to design the ammeter is the resistor

with a low resistance.

9.0 REFERENCES

Book Sources:

i. Kalsi H.S., “Electronic Instrumentation”, Second Edition, Tata

McGraw Hill, 2004.

Internet Sources:

i. Ammeter

http://en.wikipedia.org/wiki/Ammeter

ii. Ammeter Design

http://www.allaboutcircuits.com/vol_1/chpt_8/2.html

iii. Ammeter impact on measured circuit

http://www.allaboutcircuits.com/vol_1/chpt_8/5.html

iv. AMP[Shunt Ammeter Circuit

http://home.cogeco.ca/~rpaisley4/CircuitIndex.html

v. Construction of Voltmeter or Ammeter From a Galvanometer


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http://www.physics.purdue.edu/~clarkt/Courses/Physics271L/Exp4/ex

p4.html

vi. DC Ammeter

http://tpub.com/content/neets/14188/css/14188_82.htm

Documents

REPORT ASSIGNMENT 1.0 TITLE - Prospective Studentsmyweb.utem.edu.my/myweb/azdiana/downloads/report_sample.pdf · REPORT ASSIGNMENT 1.0 TITLE ... circuits, there are meters ... the