Reflection on Experiment 1: Electrical Measurement

SKEE 2133 Electronic Instrument & Measurement – Section 09

Experiment 1: Electrical Measurement

Group members:

1. Chuah Shi Yi
2. Law Jing Yi
3. Lee Wan Ting

The objective of this experiment is:

1. to perform current and voltage measurement using electrical and electronics instruments
2. to perform resistance measurement using Wheatstone’s bridge

Part A: Voltage and Current Measurement

In Part A, we are required to measure I_a, I_b & I_c using analog ammeter, and V_a & V_b  using analog voltmeter. All the measurements need to repeat twice to ensure the repeatability. After measuring all the current and voltage values, we need to calculate the value of the unknown resistor, R_x. However, the calculated R_x value is slightly different from the measured value. This might due to the actual value of 330Ω resistor might be higher than its rating.

There are some precautions for using a multimeter in order to avoid any damage. Before connecting or disconnecting a multimeter, we need to de-energize and discharge the circuit completely. Adjust the "0 ohms" reading after changing resistance ranges and before making a resistance measurement.

What I have obtained from Part A Experiment:

1. Learn how to measure the current and voltage using analog ammeter and analog voltmeter.
2. Learn how to use digital multimeter to measure resistance

Part B: Resistance Measurement – Wheatstone’s Bridge

For the second measurement, the value of R_pot is much smaller than R1. Hence, most of the current flow through R_pot and thus Vb is greater than Va.
For the first measurement, the value of R_pot is much greater than R1. Hence, most of the current flow through R1 and thus Va is greater than Vb. In Part B, we first measured the value of R_pot using digital multimeter. After that, we turned the potentiometer clockwise. The value of R_pot reduced.

To obtain the value of R_pot,balanced, the bridge must be in a balanced condition where there is no potential difference between nodes a and b (Vab = 0). Hence, R1R3 = R2R_pot. By using this equation, the value of R_pot,balanced can be obtained.

From Part B experiment, I learned how to find the value of R_pot using digital multimeter. I also learned how to obtain the voltage value, Vab that is needed to find the value of R_pot.

Some photos during the experiment:

The connection when measuring the current using analog ammeter.

While measuring the value of resistance using a digital multimeter

Adjusting the value of the voltage source.

The circuit connection for Part B experiment.

What I have obtained from this experiment:

1. Learn to measure the current, voltage and resistance using analog ammeter, analog voltmeter and digital multimeter.
2. Learn to figure out what causes the difference between the actual value and the measured value.
3. Learn how to find the value of R_pot,balanced.

Lastly, I would like to thank my lecturer, Dr. Anita, my friends and also my group members for helping us directly or indirectly throughout this experiment. Your assistance enables us to accomplish the experiment on time.