Biomedical Control Systems - FREQUENCY RESPONSE ANALYSIS (Short Questions & Answers)
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The document provides a series of short questions and answers related to biomedical control systems, focusing on concepts such as frequency response, stability, gain margin, and methods for performance specification like Bode and Nyquist plots. Key definitions include resonant peak, bandwidth, minimum phase systems, and the correlation between time and frequency responses. It also discusses the advantages of frequency response analysis and provides insights on improving system stability.
Biomedical Control Systems - FREQUENCY RESPONSE ANALYSIS (Short Questions & Answers)
- 1. BIOMEDICAL ENGINEERING – BCS – UNIT IV - SHORT QUESTIONS AND ANSWERS MATHANKUMAR.S, COORDINATOR/BME, V.M.K.V.E.C BIOMEDICAL CONTROL SYSTEMS UNIT IV-FREQUENCY RESPONSE ANALYSIS PART-A 1. Define resonant peak. It is the maximum value of magnitude of the closed loop frequency response. Larger the value of the resonant peak, more is the value of the peak overshoot of system for step input. It is a measure of relative stability of the system. 2. List the advantages of Bode plots. Transfer function of system can be obtained from bode plot. Data for constructing complicated polar and Nyquist plots can be easily obtained from Bode plot. It indicates how system should be compensated to get desired response. Relative stability of system can be studied by calculating gain margin and phase margin from Bode plot. 3. What is meant by frequency response of system? The magnitude and phase function of sinusoidal transfer function of a system are real function of frequency ω and so they are called frequency response. 4. How do you determine the stability of a system by using Nyquist criterion? For a closed loop system to be stable, G(s) H(s) plot must encircle -1+j0 points as many number of times of poles that are right hand side of s-plane and encircle if any must be in clockwise direction. 5. Define gain margin. In root locus gain K is increased, the system stability reduces and for a certain value of K, it becomes marginally stable. (Except first and second order systems). So gain margin is defined as the margin in gain allowable by which gain can be increased till system on the verge of instability. 6. What is cut-off rate? The slope of the resultant magnitude curve near the cut-off frequency is called cut-off rate.
- 2. BIOMEDICAL ENGINEERING – BCS – UNIT IV - SHORT QUESTIONS AND ANSWERS MATHANKUMAR.S, COORDINATOR/BME, V.M.K.V.E.C 7. How the gain margin and phase margin be improved? The easiest way to improve gain margin and phase margin is to reduce the gain. However this increases steady state error and makes the system sluggish. Better methods are available. These methods are adding compensating networks are compensators. 8. What are the two methods of specifying the performance of control system? i. By a set of specifications in time domain or in frequency domain such as peak overshoot, setting time, gain margin, phase margin, steady state error etc. ii. By optimality of certain function 9. List the frequency domain specifications. The frequency domain specification indicates the performances of the system in frequency domain are as follows (i) Resonant peak (ii) Cut-off rate (iii) Resonant frequency (iv) Gain margin (v) Phase margin 10. Define Bandwidth. The Bandwidth is the range of frequencies for which the system gain is more than -3db. 11. What is minimum phase system? The minimum phase systems are systems with minimum phase transfer functions. In minimum phase transfer functions, all poles and zeros will lie on the left half of s-plane. 12. Compare Bode plot and Nyquist plot analysis. Bode plot is suitable only for minimum transfer functions. But Nyquist plot analysis is suitable for both non-minimum and minimum transfer. 13. Write short note on the correlation between the time and frequency response. Correlation exists between time and frequency response of first or second order systems. The frequency domain specification can be expressed in terms of the time domain parameters ξ and ωn. For a peak overshoot in time domain there is a corresponding resonant peak in frequency domain.
- 3. BIOMEDICAL ENGINEERING – BCS – UNIT IV - SHORT QUESTIONS AND ANSWERS MATHANKUMAR.S, COORDINATOR/BME, V.M.K.V.E.C For higher order systems, there is no explicit correlation between time and frequency response. But if there is a pair of dominant complex conjugate poles, then the system can be approximated to second order system and the correlation between time and frequency response can be estimated. 14. What happens to the damping ratio and rise time if the band width is increased? A large band width corresponds to a small rise time or fast response so band width in inversely proportional to the speed of response, so as bandwidth is increased damping ratio and rise time both reduces. 15. List the frequency domain methods to find the stability of the system. The commonly used frequency domain methods to sketch the frequency response of the systems are Bode plot Polar plot Nyquist plot Nichol’s chart 16. Define phase margin. Phase margin is similar to the gain, it is possible to introduce phase lag in the system. i.e. negative angles without affecting magnitude plot of G(jω)H(jω). The amount of additional phase lag, which can be introduced in the system till the system reaches on the verge of instability is called phase margin. 17. What are the advantages of frequency response analysis? Without the knowledge of the transfer function, the frequency response of stable open loop system can be obtained experimentally. For difficult cases, such as conditionally stable systems, nyquist plot is probably the only method to analyze stability. Frequency response can be precisely applied to the systems those do not have rational transfer function. i.e. 1-TS etc. It can be extended to certain non-linear systems. The apparatus required for obtaining frequency response is simple and inexpensive and easy to use.
- 4. BIOMEDICAL ENGINEERING – BCS – UNIT IV - SHORT QUESTIONS AND ANSWERS MATHANKUMAR.S, COORDINATOR/BME, V.M.K.V.E.C 18. Give the factors of G(jw) used in the construction of bode plots. The factors of G(jw) used in the construction of bode plot are: Constant gain K Poles at the origin Poles on the real axis Zero on the real axis Complex conjugate poles, zeros. 19. What is polar plot? The polar plot of a sinusoidal transfer function G(jω) is a plot of the magnitude of G(jω) versus the phase angle/arguments of G(jω) on polar or rectangular coordinates as ω is varied from zero to infinity. 20. Write the drawback of the Nyquist stability criterion. The drawback of the Nyquist stability criterion is that unlike the root locus method, the Nyquist criterion does not give the exact location of the characteristic equation roots.