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Temperature Compensation Arrangement: Pointer Pointer

This document describes the operating principles of multirange ammeters, voltmeters, and ohmmeters. It discusses how these instruments use shunt and series resistances to select measurement ranges. It also covers how to design series and shunt ohmmeters using the half deflection method to calculate the required resistances for accurate resistance measurements.

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Abhinav Gupta
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© Attribution Non-Commercial (BY-NC)
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46 views16 pages

Temperature Compensation Arrangement: Pointer Pointer

This document describes the operating principles of multirange ammeters, voltmeters, and ohmmeters. It discusses how these instruments use shunt and series resistances to select measurement ranges. It also covers how to design series and shunt ohmmeters using the half deflection method to calculate the required resistances for accurate resistance measurements.

Uploaded by

Abhinav Gupta
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Temperature Compensation Arrangement

Scale

Pointer
Coil (Cu)

Swamping Resistors R1 R2 (M ) (Mn) (M ) (Mn) Sh t R Shunt Resistor it R3 (Cu)

Temp. increases Rcoil il increases

DC Ammeter
PMMC can be used as ammeter Im Rm

Range selection of Rsh


I Ish Rsh Im Rm

I m Rm I m Rm Rm = = Rsh = n 1 I sh I Im
where n = I/Im.

Multirange Ammeter
I R1 10A R2 R3 5A 1A S Im Rm

S I

1A 5A 10A

Im R3 R2 R1 Rm

Simple Arrangement

Ayrton Shunt Arrangement

Selection of resistances for different range

Ammeter Sensitivity y
Determined by the amount of current required by the meter coil to produce full full-scale scale deflection of the pointer

Ammeter Loading
R E I E R Im1 Rm

Im1/I =

R + R

DC Voltmeter
PMMC can be used as Voltmeter RS
Im DC Input, Vin Rm

Range selection - Rs depends on meter range

V RS = I

in m

Multirange Voltmeter
R1 R2 R3 R4

10V 50V 100V 1V S DC Input, Vin

Im Rm

Value of Resistances depends on Voltmeter range

Voltmeter Sensitivity (Ohms per volt rating)


Sensitivity S =

Ohm Volt
1 I fsd

Rm + RS = = V in

Voltmeter Loading
The insertion of voltmeter connection change the operation of circuit, is called Loading.

Ohmmeter
An instrument used to measure resistance or checking continuity

Type of ohmmeter:

1. Series Type 2 Shunt Type 2.

Series Type yp Ohmmeter


Unknown resistance is connected in series with meter
R1 I2 Rm I R2 E A Rx B

Series ohm meter Design


Half Deflection Method (To calculate R1 and R2 ) Let Rh = Half deflection resistance. For unknown Rx= Rh , I = Ifsd/2. /2 At half deflection:

R2 Rm Rh = R 1 + R2 + Rm E E , Itotal = Ih = Rh 2 Rh
R1 Rm I R2 I2 Itotal E A Rx B

Designing series ohm meter


Let Rh = Half deflection resistance. resistance For unknown resistance Rx = Rh ,I = Ifsd/2. Further, at half deflection

E Ih = 2 R

R2 Rm Rh = R 1 + R2 + Rm E , I = I - I and I R = I R 2 2 fsd m , Itotal = 2 total fsd Rh

I
R2 =

fsd

RmRh
fsd

E I

Rh

R1 = Rh -

fsd

Rm Rh E

Shunt Type
Unknown resistance is connected in parallel with meter
R1 It E S Im Rm Ish Rsh B A Ix Rx

Designing shunt ohm meter


Half Deflection Method (To calculate R1 and R2 ) Let Rh = Half deflection resistance. For Rx= Rh , I = Ifsd/2. /2 At half deflection Ix = Ish + Im
R1 E It S Im Rm Ish Rsh h B A Ix Rx

To calculate R1 and Rsh (Half Deflection Method) Let Rh = Half deflection resistance. For this value of Rx, Im = Ifsd/2. Further, at half deflection Ix = Ish + Im

Ix =

Em Rh
m

Im Rm = Rh
h

Ish = I

R Rh

) =I

fsd

R Rh

) / 2

To calculate R1 and Rsh (Half Deflection Method) Solving these equations, we get

I m Rm Rsh = I sh
It = Ish + Ix + Im = 2(Im + Ish) = 2Im(Rm/Rh)

R1 = (E ImRm)/It

Ohmmeter Scale:

Scale is logarithmic g expand p at lower end and compressed in higher range. Series type is used for relatively higher values of resistances while shunt type is used for low values of resistances.

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