analogue and digital communication

Priya is working on a project involving a data acquisition system for remote environmental monitoring. Which of the following best describes the key steps in her system, from sensor output to digital representation, and highlights the role and critical specifications of an Analog-to-Digital Converter (ADC)?

• Sensor output → Signal conditioning → Analog-to-Digital Converter (ADC) → Digital data; ADC resolution and sampling rate are critical for data accuracy.

• Sensor output → Digital-to-Analog Converter (DAC) → Signal conditioning → Digital data; ADC resolution and sampling rate are not important.

• Sensor output → Direct digital transmission without conversion; ADC is not required.

• Sensor output → Signal conditioning → Digital-to-Analog Converter (DAC) → Digital data; ADC is used only for display purposes.

Answer explanation

The correct choice outlines the essential steps: sensor output is conditioned, then converted to digital form by an ADC. The ADC's resolution and sampling rate are crucial for ensuring accurate data representation.

Arthur is working on a project that involves processing audio signals. He needs to determine the minimum sampling rate required to avoid aliasing according to the Nyquist-Shannon sampling theorem.

• Twice the maximum frequency of the signal

• Equal to the maximum frequency of the signal

• Half the maximum frequency of the signal

• Four times the maximum frequency of the signal

Answer explanation

According to the Nyquist-Shannon sampling theorem, to avoid aliasing, the minimum sampling rate must be at least twice the maximum frequency of the signal. Therefore, the correct choice is 'Twice the maximum frequency of the signal'.

Anaya is setting up a new digital communication system for her school project. She needs to calculate the bit rate of the digitized signal to ensure it meets the project requirements. Calculate the bit rate of the digitized signal.

• Bit rate = 2 kbps

• Bit rate = 8 kbps

• Bit rate = 16 kbps

• Bit rate = 64 kbps

Answer explanation

The bit rate is calculated as the product of the sampling rate and the number of bits per sample. For a typical digitized signal, a common configuration is 64 kbps, making it the correct choice.

Emily is sending a data burst over the internet that lasts for 1 second. The total number of bits transmitted per burst is:

• 1 bit

• 8 bits

• 1000 bits

• Cannot be determined from the given information

Answer explanation

The question does not provide information about the data rate or the number of bits transmitted per second. Therefore, we cannot determine the total number of bits transmitted per burst, making 'Cannot be determined from the given information' the correct choice.

• C = B log2(1 + 20)

• C = B log2(1 + 100)

• C = B log2(1 + 10)

• C = B log2(1 + 200)

Answer explanation

To find the maximum data rate using the Shannon-Hartley theorem, convert 20 dB to linear SNR: SNR_linear = 10^(20/10) = 100. Thus, the correct formula is C = B log2(1 + 100).

Charlie is working in a factory where he needs to choose between a variable frequency drive (VFD) and a star-delta starter for a 110kW motor. The environment is humid with potential for corrosive gases. Which of the following is an advantage of using a VFD in this scenario?

• Lower starting current and better speed control

• Higher mechanical stress on the pump

• Less energy efficiency during operation

• Better suitability of star-delta starter for corrosive environments

Answer explanation

Using a VFD provides lower starting current, reducing electrical stress on the motor and associated equipment. It also allows for better speed control, which is crucial in humid environments with corrosive gases, enhancing operational efficiency.

Benjamin is responsible for ensuring the reliable and safe operation of a 110kW motor installed in a humid and potentially corrosive environment. Which of the following lists the essential protection requirements for this motor, including their functions?

• Fuses, circuit breakers, thermal overload relays, moisture ingress protection, and vibration monitoring; they protect against overcurrent, short circuits, overheating, moisture damage, and mechanical faults.

• Only fuses and circuit breakers; they protect against all possible faults in any environment.

• Thermal overload relays and vibration monitoring only; they are sufficient for all motor protection needs.

• Moisture ingress protection alone; it covers all electrical and mechanical risks.

Answer explanation

The correct choice includes fuses, circuit breakers, thermal overload relays, moisture ingress protection, and vibration monitoring, which collectively safeguard against various risks, ensuring reliable and safe motor operation in harsh environments.

Elsie is working on an industrial project and needs to calculate the approximate full-load current of a 110kW motor. She must determine a suitable rating for the main circuit breaker, considering a safety factor of 1.25. (Assume a power factor of 0.88 and efficiency of 92%). What is the most appropriate rating for the main circuit breaker?

• 180A

• 220A

• 250A

• 270A

Answer explanation

To find the full-load current, use the formula: I = P / (V * PF * Efficiency). For a 110kW motor at 400V, I ≈ 265A. Applying a safety factor of 1.25 gives 331A. The nearest suitable breaker rating is 250A.

In a humid and potentially corrosive industrial setting, Eesha is responsible for ensuring proper grounding (earthing) practices for a 110kW motor and associated equipment. Why are these practices important?

• They prevent electrical shock hazards and equipment damage due to leakage currents and corrosion.

• They increase the speed of the motor.

• They reduce the need for regular maintenance.

• They improve the color of the equipment.

Answer explanation

Proper grounding practices are crucial in humid and corrosive environments as they prevent electrical shock hazards and protect equipment from damage caused by leakage currents and corrosion.

Benjamin is learning about electrical engineering and is trying to understand the relationship between Real Power (P), Reactive Power (Q), and Complex Power (S) in a power triangle. Which of the following correctly describes this relationship?

• S = P + Q

• S = √(P² + Q²)

• S = P × Q

• S = P/Q

Answer explanation

The correct relationship in a power triangle is S = √(P² + Q²). This formula shows that complex power (S) is the vector sum of real power (P) and reactive power (Q), forming a right triangle.