engineering beginner 10 sample questions

Control Systems MCQ Practice Test

Automation, feedback loops, and process control

Q1. A low-pass filter in a control system is primarily used to:

Explanation: A low-pass filter allows low-frequency signals to pass through while attenuating high-frequency signals. This is achieved by reducing the amplitude of the high-frequency components.

Q2. In a type 1 PLL (Phase-Locked Loop), what is the transfer function of the loop filter?

Explanation: In a type 1 PLL, the loop filter is typically a PI controller, which provides a balance between the phase error and the integral of the phase error. This helps to stabilize the loop and achieve lock quickly.

Q3. A controller in a temperature control system uses a PID (Proportional-Integral-Derivative) algorithm to regulate the temperature. If the setpoint temperature is 20°C and the actual temperature is 22°C, the controller will initially respond with a control action that is proportional to the

Explanation: In a PID controller, the proportional term is directly proportional to the error between the setpoint and actual temperatures. This means that the controller will initially respond with a control action that is proportional to the temperature difference between the setpoint and actual temperatures.

Q4. A triangular membership function for "positive error" rises linearly from 0 at 0 V, reaches full membership (1.0) at 2 V, and falls linearly back to 0 at 4 V. What is the degree of membership for an error of 3 V?

Explanation: On the falling edge, membership = (4 - 3) / (4 - 2) = 1/2 = 0.5. The original stem omitted the support endpoints, making the membership value indeterminate, and the options were corrupted.

Q5. A DC motor is connected to a speed controller, and the speed is measured using a tachometer. The speed controller is set to maintain a constant speed of 1000 rpm, but the motor speed is oscillating between 980 and 1020 rpm. What is the likely cause of this oscillation?

Explanation: The speed controller is not tuned correctly, resulting in an unstable closed-loop system. This can cause the motor speed to oscillate around the setpoint.

Q6. A type-1 fuzzy logic controller is implemented in a control system to control the speed of a DC motor. The input to the fuzzy controller is the error between the desired speed and the actual speed, and the output is the duty cycle of the pulse-width modulation (PWM) signal. If the membership function of the error is triangular with a peak at 2 and a base width of 4, and the membership function of the output is triangular with a peak at 0.6 and a base width of 0.8, what is the type of defuzzification method used in this system?

Explanation: In a type-1 fuzzy logic controller, the centroid method is a common defuzzification method used to calculate the crisp output value from the fuzzy output set. It calculates the center of gravity of the area under the surface, which represents the weighted average of the output values based on their membership grades.

Q7. In a PI controller, increasing the integral action (decreasing Ti) has what effect on steady-state error and overshoot?

Explanation: Stronger integral action drives the accumulated error to zero more quickly (removing offset) but adds phase lag, which typically increases overshoot and settling oscillation.

Q8. A type-1 Wind Turbine Generator (WTG) is modeled as a first-order system with a transfer function <img src=""/> G(s) = µ²² / (s + a). Given that the damping ratio (κ) is 0.5 and the natural frequency (φ_n) is 1 rad/s, determine the value of the damping coefficient (a) in the transfer function.

Explanation: The transfer function G(s) = µ²² / (s + a) represents a first-order system. The damping ratio (κ) and natural frequency (φ_n) are not directly applicable to a first-order system in the same way they are to a second-order system. However, the parameter 'a' in the denominator is related to the time constant of the system. In this case, the relationship between 'a', the damping ratio (κ, which is often implicitly 0.5 in this context, as the question states), and the natural frequency (φ_n) can be derived from the context of the question, which implies a second-order system behavior. For a second-order system, the standard form of the transfer function is G(s) = ω_n² / (s² + 2ζω_n s + ω_n²), where ζ is the damping ratio, and ω_n is the natural frequency. Comparing the given transfer function to the standard form, and considering the damping ratio and natural frequency, the correct relationship is a = 2 * κ * φ_n. Therefore, substituting the given values, a = 2 * 0.5 * 1 = 1.

Q9. A type 1 fuzzy logic controller is used to control the speed of an electric motor. The input membership function is a trapezoidal function with a core value of 30 and a support value of 20-50. What is the type of the fuzzy logic controller?

Explanation: A type 1 fuzzy logic controller is a type of fuzzy logic controller that uses a single membership function to describe the input or output variables. In this case, the input membership function is a trapezoidal function, which is a specific type of membership function.

Q10. A PI (Proportional-Integral) controller is used to control a system with a transfer function given by G(s) = (s + 2)/(s(s + 5)). The PI controller is designed with a proportional gain of 2 and an integral time constant of 10 seconds. What is the closed-loop transfer function of the system?

Explanation: The PI controller transfer function is Gc(s) = Kp + Ki/s, where Kp is the proportional gain and Ki is the integral gain. The integral time constant Ti is related to Ki by Ti = Kp/Ki. Therefore, Ki = Kp/Ti. In this case, Kp = 2 and Ti = 10, so Ki = 2/10 = 0.2. Thus, Gc(s) = 2 + 0.2/s = (2s + 0.2)/s. The plant transfer function is G(s) = (s + 2)/(s(s + 5)). The closed-loop transfer function T(s) is given by T(s) = (Gc(s) * G(s)) / (1 + Gc(s) * G(s)). Substituting the values, T(s) = ((2s + 0.2)/s * (s + 2)/(s(s + 5))) / (1 + (2s + 0.2)/s * (s + 2)/(s(s + 5))). Simplifying, T(s) = (2s^2 + 4s + 0.4) / (s^3 + 7s^2 + 10s + 0.4).

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Control Systems MCQ Practice Test | Mind Hustle