KING ABDULAZIZ UNIVERSITY

THE COLLEGE OF ENGINEERING, THE KINGDOM OF

SAUDI ARABIA

EE303

ELECTRICAL MEASRMENT & INSTRMENT

SPRING 2013

EXPERIMENT # 5

Design an Ayrton Shunt Ammeter

GROUP # 4

Team Member Group ID Section

Fahad Mohammad Al-Jdanni 1008538 DA

Faisal Alawi Baroom 1007396 DA

Mazen Almuqati 1007539 DA

Abdulaziz Hammouda 1007055 DA

Lab. Instructor: Mohammad Mottahir

Experiment Date: 12. March. 2013

Lab. Time: Sunday 11:00 – 1:00

1

Experiment No.5

Introduction

This lab will be about modifying movement ammeter to be able to measure different

ranges rather than only 1mA . The used Technique to perform that is by converting the 1

mA meter movement (galvanometer) using shunt resistors to Ayrton shunt Ammeter.

This method typically used to increase the range of a galvanometer. Before perform this

experiment, it is important to calculate the internal resistor of the galvanometer. Then the

steps of this experiment will be applied.

objectives

The objective of this experiment is to design an Ayrton shunt ammeter that provides the

following ranges

Range1: 0 5 IFS = 5 mA

Range2: 0 10 IFS = 10 mA

Range3: 0 20 IFS = 20 mA

Materials Required

1 mA meter movement

DC power supply

Variable Resistor boxes

Wire for connection

2

Theory

The following approach explains how to convert galvanometer to Ayrton shunt ammeter.

Figure 1.Schematic diagram of ayrton shunt ammeter

We need firstly to connect 3 resistor in the same configuration as Figure1

then, we need to find out the values of those resistors as following:

we apply to each switch position, where K represent the range factor (desired full scale)

Rme : the internal resistor of galvanometer

Rsh= (IFS × Rme)/(IT - IFS) = (IFS × Rme)/( K×IFS - IFS) = (Rme)/( K-1)

position 1 (5 mA), k=5

Rsh1 = (Rme)/( K-1)

R1+R2+R3 = (Rme)/(k-1)

R1+R2+R3 = (Rme)/(4) ................................ eq1

position 2 (10 mA), k=10

Rsh2 = (Rme)/( K-1)

R1+R2+R3 = (R`me)/(k-1) where R`me = Rme +R3

R1+R2 = (Rme +R3)/(9) ................................ eq2

position 2 (20 mA), k=20

Rsh2 = (Rme)/( K-1)

R1+R2+R3 = (R``me)/(k-1) where R``me = Rme +R3 +R2

R1 = (Rme +R3 +R2)/(19) ................................ eq3

By solving eq1,eq2, & eq3 ; we can find out the value of R1 , R2 , & R3.

3

Lab Safety

Before moving ahead, we have to take a look at the following instructions that we should

follow it during the lab time.

General safety instructions

1. Move carefully in the lab.

2. No eating, no drinking and no smoking in the lab.

3. Use appropriate and available safety precautions and tools.

4. Never use chairs or boxes to reach to high places.

5. Concentrate to your experiment and equipment.

6. Don't keep any liquid close or on-top of any electrical device.

7. While doing experiment , be sure of the followings :

Connect circuit wiring carefully, let lab engineer check it.

Keep away any wire or equipment not used.

If you need to do any change in your circuit, switch power off, do necessary

modifications, double check –it, then switch power on .

Component and hand should be dry while doing the experiment.

If you got unexpected results ask assistance of responsible.

Never touches or play with denuded wires or cables.

After finishing the experiment, switch-OFF the equipment then botches put back all

components and wires in their places.

Safety rules of electrical laboratories: 1. Proper the grounding for lab .Power-Supply and equipment.

2. Fire extinguisher fixed in appropriate places.

3. Emergency exit signs for any emergency case.

4. Coincidence of power cables /plugs and current loads – regular check of cables and

wires insulation.

5. Cables should be in insulated trunks.

6. Warning tags for high voltage or radiating equipment.

7. First aid kit in appropriate place and well equipped.

4

Steps

1. Connect the positive terminal of the power supply to the variable resistor box

(RB1).

2. Connect the negative terminal from the variable resistor box (RB1) to the

positive of the 1mA meter movement. Set the resistor box to be 10KΩ.

3. Connect the circuit by connecting the negative terminal of the 1mA meter

movement to the negative terminal of the power supply

4. Adjust the power supply to 10 volts. Note that the meter movement will not

give 1mA exactly which means there is internal resistor of meter movement.

5. Decrease the variable resistor box (RB1) until the meter movement reach of

full scale deflection (1mA).

6. Connect another variable resistor box (RB2) parallel to the 1mA meter

movement.

7. Increase the variable resistor box (RB2) until the pointer of 1mA meter

movement become in the half of the full scale deflection (0.5mA). Note the

value of the second variable resistor box (RB2) represents the internal resistor

value (Rm).

8. Calculate the Rsh (shunt register) by using the law: Rsh = , k=

9. To convert a 1mA meter movement into ammeter with range (0-5mA),

calculate the value of Rsh1 by using the law: Rsh1 = = R1+R2+R3 (equation

1).

10. Adjust the variable resistor box (RB2) to value of Rsh1.

11. Adjust the variable resistor box (RB1) to value : 2000Ω

12. If the ammeter pointer (that was meter movement) not reaches to full scale

(5mA) or indicate more of full scale, calculate the percentage of error by using

the error law.

13. To convert a 1mA meter movement into ammeter with range (0-10mA),

calculate the value of Rsh2 by using the law: Rsh2 = = R1+R2 (equation

2).

14. Adjust the variable resistor box (RB2) to value of Rsh2.

15. Connect variable resistor box (RB3) series with ammeter. Adjust (RB3) to value

of R3.

16. Adjust the variable resistor box (RB1) to value : 1000Ω

17. If the ammeter pointer (that was meter movement) not reaches to full scale

(10mA) or indicate more of full scale, calculate the percentage of error by

using the error law.

5

18. To convert a 1mA meter movement into ammeter with range (0-20mA),

calculate the value of Rsh3 by using the law: Rsh3 = = R1 (equation 3).

19. Adjust the variable resistor box (RB2) to value of Rsh3.

20. Adjust variable resistor box (RB3) to value of (R3+R2).

21. Adjust the variable resistor box (RB1) to value : 500Ω

22. If the ammeter pointer (that was meter movement) not reaches to full scale

(20mA) or indicate more of full scale, calculate the percentage of error by

using the error law.

23. Note: before the conversion process, calculate the value of R1, R2 and R3 by

using the equation 1, 2 and 3.

24. Calculate the percentage of error by using: % error =

.

Results & Calculations

The ammeter resistance was measured by:

Rm = 160 Ω

To calculate the three resistors needed to design the Ayrton shunt ammeter we have these

three equation:

1) R1 + R2 + R3 = ( Rm / K1 – 1 )

2) 9 R1 + 9 R2 - R3 = Rm

3) 19 R1 - R2 - R3 = Rm

Where K1=5

After solving these three equation the resistors value is:

R1 =10 Ω , R2 =10 Ω , R3 =20 Ω

To move 5 mA current we need:

V =10 V, R = 2K Ω

The measured value by the ammeter was exactly like the actual value which is 10 V

across the 2K Ω give as 5 mA so the error was zero.

To move 10 mA current we need:

V =10 V, R = 1K Ω

The measured value by the ammeter was 9.1 V across the 1K Ω give as 10 mA so the

error was:

6

%error =

To move 20 mA current we need:

V =10 V, R = 0.5K Ω

The measured value by the ammeter was 8.8 V across the 0.5K Ω give as 20 mA so

the error was:

%error =

Comments

It is clear that when we increase the ammeter scale (from 5 mA to 10 mA or 10 mA to

20 mA) the errors we get while measuring the current increase. This increase in errors

came from that when we increase the scale we increase the resistance that come with the

ammeter resistance in series. Since we increase series resistance with ammeter resistance

the total resistance in our design decrease so that the errors in measuring ammeter

resistance become more significant than before.

Conclusion

After finishing this experiment, and after we have learned that the internal resistance of

any measurement device effects in the readings from the previous experiments, we used

in this experiment the internal resistance and shunt resistances in order to help us to

convert a basic movement ammeter that read till 1mA into a basic movement ammeter

that read till several scales such as 5,10,20 mA, which is extremely helpful in order to let

students know about manipulating in the devices functions. Finally, we hope that this

report gained the acceptance.