LAB 1 ELECTRONIC INSTRUMENTATION

 

 

NDJ 30003 – ELECTRONIC INSTRUMENTATION

                        LAB 1 D’ARSONVAL GALVANOMETER

list of contents:

• Exercises
• Discussion 
• Conclusion

Exercises

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	15.51	10	460	1.2	1.09	10	1.085	1.1	1.3
			5	420		1.07	12		1.2
			2	320		1.10	9		1.6
	220	6.77	10	200		1.00	20		1.07
			5	180		1.11	8		1.2
			2	140		1.14			1.6

calculation:

1. To obtain the value of Vfs 

-R1= 150

    Rs = 10 ohm

    Rs = 5 ohm

     Rs = 2 ohm 

   

R1= 220 ohm 

    Rs = 10 ohm 

    

    Rs = 5 ohm 

   

     Rs = 2 ohm

Manual calculation:

Discussion 

 -using load resistor. 

   10k 

   100k

Observation: As you can see, when the load resistor is connected in parallel, the voltage rises.

-using internal resistance voltmeter.

    1M

 

    10 M

    100 M

Conclusion

        When dealing with the measurement of voltages of circuit connections, it appears that the internal resistance of the voltmeter plays an essential role. If the second circuit connection is correct, the voltage across R2 should be 7.5V. However, when connecting the R2 parallel in order to obtain the voltage across it, it will slightly decrease the voltage across the resistor. The formula to find the resistor that connect parallel is:

   Rt = Ra(Rx) / (Ra + Rx )

        Assume Ra is the R2 in the above circuit and R1 in the discussed circuit both have a constant value of 5, and Rx is the value of the voltmeter's internal resistance. If the voltage source is 10V, both resistors connected in series will get an equal voltage of 5V (R1=5, Ra=5).

        Finally, when measuring across the resistor, the reduced internal resistance of the voltmeter might completely change the value of the real voltage. As a result, the higher the voltmeter's internal resistance, the more precise the reading and measurement of voltage across the resistance.