Control System & PLC – Objective Questions

 

📘 Control System & PLC – Objective Questions 

Unit 2 – Control System Fundamentals

  1. A control system without feedback is called: Open loop ✅

  2. A control system with feedback is called: Closed loop ✅

  3. Transfer function is defined as: Output/Input in Laplace domain ✅

  4. Poles on the right half of S‑plane indicate: Unstable system ✅

  5. Negative feedback improves: Stability ✅

  6. Root locus is plotted in: S‑plane ✅

  7. The stability of a system can be checked using: Routh–Hurwitz criterion ✅

  8. Time response of a system is analyzed in: Time domain ✅

  9. Frequency response of a system is analyzed in: Frequency domain ✅

  10. The steady‑state error decreases with: High gain ✅

Unit 3 – Stability Analysis

  1. Routh array is used to determine: System stability ✅

  2. A system is stable if all poles lie: In LHS of S‑plane ✅

  3. Gain margin is measured from: Bode plot ✅

  4. Phase margin is measured from: Bode plot ✅

  5. Nyquist plot is used for: Stability analysis ✅

  6. A system is marginally stable if poles lie: On imaginary axis ✅

  7. The characteristic equation is obtained from: Denominator of transfer function ✅

  8. The order of a system is equal to: Highest power of s in denominator ✅

  9. The damping ratio determines: Nature of transient response ✅

  10. A critically damped system has damping ratio: 1 ✅

Unit 4 – PLC Basics

  1. PLC stands for: Programmable Logic Controller ✅

  2. PLCs are widely used in: Industrial automation ✅

  3. Ladder logic is based on: Relay logic diagrams ✅

  4. PLC input modules are used to: Receive signals from sensors ✅

  5. PLC output modules are used to: Control actuators ✅

  6. A rung in ladder logic represents: One control operation ✅

  7. PLC timers are used for: Time delay operations ✅

  8. PLC counters are used for: Counting events ✅

  9. PLC memory stores: Programs and data ✅

  10. PLCs are preferred over relays because: They are flexible and programmable ✅

Unit 5 – PLC Applications & Advanced Instructions

  1. A PLC sequencer is used for: Step‑by‑step control ✅

  2. PLC shift registers are used for: Data shifting operations ✅

  3. PLCs can be programmed using: Ladder logic ✅

  4. PLCs are used in motor control for: Start/stop and protection ✅

  5. PLCs reduce wiring compared to: Relay logic systems ✅

  6. PLCs can be connected to: SCADA systems ✅

  7. PLCs are used in elevators for: Automatic control ✅

  8. PLCs are used in packaging industries for: Sequential control ✅

  9. PLCs are used in traffic lights for: Timing control ✅

  10. PLCs are used in robotics for: Motion control ✅

Mixed Numerical/Conceptual MCQs

  1. For T(s)=10s+5, the pole is at: s = –5 ✅

  2. For T(s)=s+2s2+3s+2, poles are at: –1, –2 ✅

  3. For T(s)=10s(s+2), zeros = none, poles = 0, –2 ✅

  4. A system with poles at –2, –3 is: Stable ✅

  5. A system with poles at +2, –3 is: Unstable ✅

  6. A system with poles at ±j2 is: Marginally stable ✅

  7. The gain margin is positive if: System is stable ✅

  8. The phase margin is negative if: System is unstable ✅

  9. PLC timers can be: ON‑delay or OFF‑delay ✅

  10. PLC counters can be: Up counter or Down counter

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