Galvanometer as Ammeter/ Voltmeter

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Galvanometer as Ammeter/ Voltmeter
Galvanometer_diagram.svg?
Using Right hand Rule Force F is developed while
Flux density B from permanent magnet along
with I Current passing through the coil is
present
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Application of Ammeter/Voltmeter
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Moving Coil Ammeter
Linear Scale due to Moving Coil
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Moving Iron Ammeter
Non-linear Scale Due to Moving Iron
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Ammeter

• An ammeter consists of a galvanometer with a
  shunt resistor. The input current iin

divides with im passing through the meter and
ish Passing the shunt. It is clear from Fig
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Design of Ammeter

• If Rm50 ohm and it is required that full scale
  capability of 1 mA is to measure up to 5 A

Rsh 0.00150/(5-0.001) 0.01 Ohm
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Voltmeter

• Galvanometer is used as a voltmeter by connecting
  a series resistor Rse
• where current remains
• same but total
• resistance is
• extended to extend
• the scale.

Vin Vm Vse
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Design of Voltmeter

• A full scale 1 mA Galvano of 50 0hm to measure 5
  Volt FS

Rse (5/0.001)- 50 4950 Ohms
A series resistance of 4950 Ohm will enable the
same to read FS 5 Volts
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Electrodynamometer
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Electrodynamometer

• Wattmeter

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Wattmeter

• The fixed coil of the wattmeter is connected in
  series with the circuit (load), and the moving
  coil is connected across the line. When line
  current flows through the fixed coil of a
  wattmeter, a field is set up around the coil. The
  strength of this field is in phase with and
  proportional to the line current. The moving coil
  of the wattmeter generally has a high-resistance
  resistor connected in series with it. The purpose
  for this connection is to make the moving-coil
  circuit of the meter as purely resistive as
  possible. As a result, current in the voltage
  circuit is practically in phase with line
  voltage. Therefore, when voltage is impressed on
  the voltage circuit, current is proportional to
  and in phase with the line voltage.

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V
I
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Tutorials
Where Ti Torque developed due to
current N No of turns of the coil carrying
current ? Flux density created by the
magnet L axial length of the coil under the
pole D mean diameter of the coil I current
passing through the coil
Where Tc torque developed in Control
spring k stiffness constant of the spring ?
angular deflection turned due to current
While Ti Tc
Where S sensitivity or calibration constant of
the meter
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Tutorial ..

• Full scale range of GALVANO is 25uA, while full
  deflection is 45 degree. Determine the
  sensitivity S

Therefore S ?/i S 45/25x10-6
40000deg/A
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Assignment 1

• Q.No 1 A galvano of 3 Ohm resistance reads a
  maximum current of 150 milliampere. How can it be
  used for
• A voltmeter to read upto 15 volts
• An ammeter to read upto 30 ampere
• Q.No 2 In a voltmeter the moving coil consists
  of 100 turns wound on a square former has a
  length of 3 cm and a flux density in the air 0.06
  Wb/m3. Calculate deflecting torque when the coil
  is carrying a current of 12 milliampere.

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Strip Chart Recorder

• This utilizes a servomotor-driven null-balance
  potentiometeric circuit. Input is amplified
• and fed to servo amplifier to produce error
  signal using feedback. Servo motor poition
• wiper and pen across moving chart for recording
  signals.

Reference Voltage
Feedback
Printer roller
Wiper Pen drive

Zero set
Chart paper
_
Input signal
Signal amplifier
Servo amplifier
Servo motor
Gear Dive
Reference voltage -
Synchronous Motor
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Typical Specifications ofChart Recorder
Paper width 120-250mm
Sensitivity 5mV to
100V Speed 25mm/h to 250mm/h
Response Time 0.5 seconds
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Typical Applications

• Any time varying variable can be manipulated for
  record
• on Chart Recorders as part of overall Database
  such as
• ECG
• Weather Forecast
• Temperature
• Pressure
• Humidity
• Seismic History

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X-Y Recorders

• Working of the recorder is again based on dual
  servo motor-driven null-potentiometric circuits
  as described in Chart Recorder.
• Paper is stationary rather than
• rolling along time.
• Pen is controlled in both axes
• x and y direction.
• The recorder may have
• single or multiple pens
• with different colors
• Many have time base
• available for time varying
• quantities.