Measurement, Instrumentation and Control
NEC Electrical and Electronic Engineering · 630 practice MCQs
The chapter on Measurement, Instrumentation and Control is crucial for aspiring engineers preparing for the NEC licensing exam. It covers essential concepts such as the characteristics of PMMC instruments, root locus behavior, and the significance of Nyquist plots.
Understanding these topics not only helps in answering exam questions effectively but also lays a strong foundation for practical applications in electrical and electronic engineering. To prepare, engage with our 630 practice MCQs that simulate real exam conditions and enhance your mastery of this chapter.
Sample questions with answers
1.About which axis is the root locus symmetrical?
- A.Imaginary axis
- B.Real axis
- C.Only zeros
- D.Origin
Why: The root locus is symmetrical about the real axis because the complex conjugate poles and zeros ensure that for every point in the complex plane, there is a corresponding point that mirrors it across the real axis.
2.For what type of measurements are PMMC instruments appropriate?
- A.High-frequency AC
- B.Only DC measurements
- C.Both AC and DC
- D.Only AC measurements
Why: PMMC (Permanent Magnet Moving Coil) instruments are designed to measure direct current (DC) because their operation relies on the magnetic field produced by a constant current, making them unsuitable for high-frequency AC measurements.
3.What characterizes a critically damped second-order response?
- A.Gradual rise
- B.Quickest rise without overshoot
- C.Only undershoot
- D.Oscillating behavior
Why: A critically damped second-order response is characterized by the fastest rise to the final value without overshooting, which is essential in control systems to achieve stability without oscillation.
4.What happens with root locus for pairs of complex poles?
- A.Only reach the origin
- B.Indeterminate outcome
- C.Loci move out symmetrically into the complex area
- D.Stay along the real line
Why: When there are pairs of complex poles, the root locus will move out symmetrically into the complex area as the gain increases, reflecting the system's behavior in response to changes in feedback.
5.What does a Nyquist plot encircling the -1 point signify?
- A.No importance
- B.Shows instability
- C.Shows marginal stability
- D.Shows stability
Why: A Nyquist plot encircling the -1 point indicates that the system has crossed into the unstable region, thus showing instability in the feedback loop.
6.What can be done to enhance damping in a PMMC instrument?
- A.By increasing the number of coil turns
- B.Using an eddy current disc
- C.Increasing spring stiffness
- D.Using a multiplier resistor
Why: Using an eddy current disc in a PMMC instrument enhances damping by creating a magnetic drag force that opposes the motion of the coil, reducing oscillations and improving stability.
7.When does the root locus appear on the real axis?
- A.Odd count of real-axis poles and zeros
- B.Only zeros
- C.Just even counts
- D.Only poles
Why: The root locus appears on the real axis when there is an odd count of real-axis poles and zeros, as this configuration allows for a continuous path of the locus between the poles and zeros.
8.What does a tachometer measure?
- A.Speed of rotation
- B.Current
- C.Voltage
- D.Resistance
Why: A tachometer measures the speed of rotation, typically of a shaft or wheel, providing a direct indication of how fast something is spinning.
9.In the force-voltage analogy, what represents a mechanical spring?
- A.A resistor
- B.A current source
- C.An inductor
- D.A capacitor
Why: In the force-voltage analogy, a mechanical spring is represented by a capacitor, as both store energy and exhibit a linear relationship between force and displacement or voltage and charge.
10.What does the Maxwell bridge mainly measure?
- A.Inductance
- B.Resistance
- C.Frequency
- D.Capacitance
Why: The Maxwell bridge is primarily used to measure inductance by balancing the bridge circuit with known components, allowing for precise determination of an unknown inductor's value.
11.What are load cells commonly constructed with?
- A.Strain gauges
- B.LVDTs
- C.Inductors
- D.Thermistors
Why: Load cells are commonly constructed with strain gauges, which convert mechanical deformation into an electrical signal, effectively measuring weight or force.
12.What does asymptotic stability mean?
- A.Oscillates indefinitely
- B.Grows without bounds
- C.Stays constant
- D.State approaches equilibrium as time goes to infinity
Why: Asymptotic stability means that as time progresses towards infinity, the system's state will approach equilibrium, indicating that it will settle down and not diverge or oscillate indefinitely.
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Frequently asked questions
- About which axis is the root locus symmetrical?
- The root locus is symmetrical about the real axis.
- For what type of measurements are PMMC instruments appropriate?
- PMMC instruments are appropriate for measuring direct current (DC) values.
- What characterizes a critically damped second-order response?
- A critically damped second-order response returns to equilibrium without oscillating and is the fastest response without overshoot.
- What happens with root locus for pairs of complex poles?
- For pairs of complex poles, the root locus will appear as complex conjugate pairs that move in a circular path in the s-plane.
- What does a Nyquist plot encircling the -1 point signify?
- A Nyquist plot encircling the -1 point signifies potential instability in the control system.