LAB 1 - D’ARSONVAL GALVANOMETER



 

UNIVERSITI MALAYSIA PERLIS

 

 

 

 

 

NDJ 30003 – ELECTRONIC INSTRUMENTATION

 

 

 

LAB 1 

 

D’ARSONVAL GALVANOMETER

 

 

Prepared by:

Ts. Ahmad Syahir Bin Ahmad Bakhit

 

 


               Name               :  IRFAN BIN RAMZAN

               Matrix No.      : 192020084

               Program          : COMPUTER ENGINEERING

             Date                 : 13/9/2021


OBJECTIVES

To find the internal resistance and the current sensitivity of the galvanometer.

INTRODUCTION

The galvanometer contains a coil of wire in a magnetic field, which will experience a torque when a current passes through the wire of the coil.  The coil is attached to a pointer and a spring so that the amount of deflection of the pointer is proportional to the current in the wire of the coil.

The value of the load resistor (R1) will be set to a specified value and the potential difference provided by the power supply will be varied to obtain a full-scale deflection of the pointer of the galvanometer.  The voltage (VFS) required to obtain full-scale deflection will be recorded, without changing the applied voltage (VFS), Add a shunt resistor (RS) in parallel with the galvanometer.  Vary the load resistance to get the full-scale deflection in the galvanometer.  The new load resistance, R2 will be recorded.  In both circuits, the potential difference supplied by the power supply is the same as is the current passing through the galvanometer (full-scale deflection in both circuits). 


EXERCISE


1.      Set the potentiometer to 510Ω.  Connect the circuit as in the Figure 1.1 and keep the voltage source in minimum position such that voltage output from the voltage terminals are 0V.  



                                              Figure 1.1:  Set up of circuit connection 

2.      Increase the voltage supply and the galvanometer pointer will deflect towards right hand side or left hand side. You can replace the galvanometer with the DMM/Ammeter in the Multisim. Assume Rg is 1.2 Ω for the given galvanometer. Vary the voltage supply until the galvanometer shows its maximum deflection, which the pointer should comes to 30 positions (divisions). 


3.     Connect the multimeter across the voltage terminal to measure the voltage and record this value as VFS.  


4.     Turn OFF the supply and do not disturb the voltage source.  Now connect the resistance, RS and construct the circuit as in Figure 1.2.  Select the 10 Ω for RS. Switch ON the instrument, then the pointer of the galvanometer will return back by a few divisions.  




Figure 1.2:  The circuit diagram with shunt resistor, RS

5.    Without disturbing the voltage source, adjust the potentiometer, R2 until the pointer scale comes to full scale deflection which is 30 positions (divisions). 

 

6.   Turn OFF the supply and disconnect R2. Measure the absolute values of R2 using multimeter and record the value in the Table 2.1.

 

7.  The values of VFS, R1, R2, RS, are known, determine the galvanometer resistance, Rg by calculation.  Then calculate its current sensitivity, K. Repeat from step 5 for RS = 5 Ω and 2 Ω and R1 = 220 Ω.

 

8.     Finally disconnect the galvanometer from the circuit and connect multimeter across the terminal of galvanometer to measure its internal resistance.  Record the value as Rg (measured).

. 

RESULTS


N

R1 (Ω)

VFS

(V)

Rs (Ω)

R2 (Ω)

 

Rg Ω

 

Mean of Rg

K

(A/div)

Mean of K

Meas.

Calc.

%e

30

 

510

 

15.34

10

450

1.2

1.33

10.83

1.39

0.53m

0.55m

5

410

1.23

2.50

0.55m

2

300

1.40

16.67

0.59m

 

220

 

6.64

10

190

1.58

31.67

0.52m

5

170

1.47

22.50

0.54m

2

130

1.39

15.00

0.59m



ANSWER


R1 = 510Ω, VFS = 15.34V 



RS = 10Ω, R2 = 450Ω



RS = 5Ω, R2 = 410Ω



RS = 2Ω, R2 = 300Ω



R1 = 220Ω, VFS = 6.64V 



RS = 10Ω, R2 = 190Ω



RS = 5Ω, R2 = 170Ω



RS = 2Ω, R2 = 130Ω



Calculation:




DISCUSSION

 

1)
 
RL = 10kΩ


RL = 100kΩ



2)

 

1MΩ



10MΩ



100MΩ




Conclusion:

 

Throughout these lab activities, based on the tabulated data obtained from the experiment, it is safe to concluded that D’Arsonval Galvanometer (replaced with voltmeter particularly in this experiment) are sensitive to the change of resistance in the circuit adjusted by potentiometer.

As the Rs value drop, we can see how the current also drop in response. This strongly support the basic rules of voltage, resistance and current which V=I/R. As the voltage value are to be remain constant, only the current value would change in response to the changes of resistance value. 









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