Reflection on SKEE 2133 Experiment 1: Electrical measurement
by LEE WAN TING
NAME: LEE WAN TING
MATRIX NO: A18KE0096
On 23 of October, 2019, experiment 1 for course Skee 2133, section 9 and 10 was being carried out under the administration of Dr. Anita Binti Ahmad. There were 2 parts needed to be done in this experiment.
In part A of experiment 1, the circuit was set up as the diagram shown. Analog ammeter was used to measure the currents Ia, Ib and Ic by placing it in the circuit in series. While for voltage Va and Vb measurements, analog voltmeter was used in parallel in the circuit. All the measurement were obtained twice and each average value was taken for calculation. The suitable range for each measurement was chosen to prevent damage on the particular component.
By using Kirchhoff’s current law and Ohm’s law, the value of resistance Rx was obtained which is 155.7Ω. After that, the value of unknown resistance Rx was verified by using digital multimeter, which is 110Ω. There was a difference for Rx value which the calculated value (155.7 Ω) was higher than directly measured value (110 Ω). This was due to the small difference in actual resistance and experimental resistance which caused by the imperfection of manufacturing, surrounding temperature of experiment and also the tolerance in a resistor. Since all the theories used including Kirchhoff’s current law and Ohm’s law is assumed to be ideal, this also made a difference between theoretical value and practically measured value.
In part B of experiment 1, the circuit diagram was first drawn in a simple way before setting up. The experiment came out with a result of changing on digital multimeter when the potentiometer was being turned. As the button on potentiometer turned clockwise, the resistance of potentiometer decreased, caused the measured value of Vb, voltage across 150 Ω resistor to increase. Based on the mathematical approach, the value of Vab decrease till a negative value obtained.
When the value of potentiometer, Rpot was larger than 39kΩ, more current from 9V supply will flow through 39kΩ and then 330Ω resistors. So, the value of Va which is voltage across 330Ω resistor was higher than value of Vb. On the other hand, the value of Va was smaller than Vb when the value of Rpot was smaller than 39kΩ, this caused a zero difference or negative value for calculation of Vab. Besides, the value of Rpot, balanced was determined which was 17.7kΩ by using Wheatstone’s bridge null balance condition and 18.1k Ω by using digital multimeter measurement. These 2 results showed again theoretical value was slightly different from experimental value due to surrounding conditions and nature tolerance in component.
During whole experiment, some precautions were taken to prevent effect on exactness of every value. The circuit was deenergized and discharged from the supply before charging and discharging to the digital multimeter and analog meters. The circuit was ensured not being applied with power when measuring resistance. The digital multimeter was always switched off after each measurement. For every current and voltage measurement by using analog meter, the range used always started with the highest one followed with the lower range. All the measurement were obtained twice and each average value was taken for calculation. The suitable range for each measurement was chosen to prevent damage on the particular component.