1. 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:

2. Application of Ammeter/Voltmeter

3. Moving Coil Ammeter
Linear Scale due to
Moving Coil

4. Moving Iron Ammeter
Non-linear Scale
Due to
Moving Iron

5. 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:

6. Design of Ammeter
If Rm=50 ohm and it is required that full scale capability of 1 mA is to measure up to 5 A:
Rsh = 0.001*50/( )
0.01 Ohm

7. 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

8. 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

9. Electrodynamometer

10. Electrodynamometer
Wattmeter

11. 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.  V I

12. Tutorials While Ti = Tc Tc torque developed in Control spring
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

13. 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

14. 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.

15. 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.
Feedback
Reference Voltage +
Printer roller
Wiper & Pen drive +
Zero set
Chart paper _
Input signal
Signal
amplifier
Servo amplifier
Servo motor
Gear Dive
Reference voltage -
Synchronous Motor

16. Typical Specifications of Chart Recorder
Paper width: mm; Sensitivity: mV to 100V
Speed: mm/h to 250mm/h Response Time: seconds

17. Typical Applications ECG Weather Forecast Seismic History Temperature
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

18. 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.