Engineer

Tutorial 01

DC Ammeter
Example 2-2 A 200-µA meter movement with an internal resistance of 550-Ω is used in 0- to 500-mA ammeter. Find the value of the required shunt resistance.

Ayrton Shunt
Im
Rm

I - Im

Rc

Rb

Ra

I2 I3 I I1

Example 2.3: Compute the value of the shunt resistors for the circuit. Given that Rm = 1.2kΩ, Im =150 µA, I1=5mA, I2=50mA, I3=200mA. Check : Rsh = Ra + Rb + Rc always!

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Fig. 3: An Ammeter using Ayrton shunt.

Ammeter Insertion Effects
Example 2.4: A current meter having an internal resistance of 100Ω is used to measure the current trough Rc in figure below. Determine the percentage of error due to the ammeter insertion. Given that Ra=Rb=Rc= 2.2kΩ
Ra

E = 5V

Rb

Rc

DC Voltmeter
Example 3.
• Calculate the values of Rs for the multiplerange DC Voltmeter circuits as shown below:but change the range to 3mV, 3V and 300V.

Rm = 2 kΩ

Ifs = 100µA
Rs1 Rs2 Rs3

3mV

3V

300 V

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DC Voltmeter
Example 4.
• Calculate the values of Rs for the multiplerange DC Voltmeter circuits as shown below: but change the range to 5mV, 5V and 100V.
Rc Rb Ra

Rm = 2 kΩ

Ifs = 50µA
5mV 5V 100V

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Voltmeter Loading Effects
Example 5:

• Two different voltmeters are used to measure the voltage across RB in the circuit below. The meters are:
Meter A : S= 10kΩ/V;Rm=0.2kΩ; Range =5V Meter B : S=20kΩ/V;Rm=2.2kΩ; Range = 5V
RA E = 20V

10kΩ

Calculate: – Voltage across RB without any meter. – Voltage across RB when meter A is used. – Voltage across RB when meter B is used. – Loading Errors in both voltmeter readings.

RB

1.8kΩ

Voltmeter Loading Effects
Example 6: • Find the voltage reading and the percentage of loading error of each reading obtained with a voltmeter on: E = 20V – Its 10-V range. – Its 50-V range – Its 200-V range. The meter has a 30-kΩ/V sensitivity and connected across RA.

RA

2.2kΩ

RB

8.2kΩ

Ohmmeter
• Find the value of R, ¼ scale, ½