Anna University Coimbatore 2008 B.E Electrical and Electronics Engineering Control system QB unit 1 - Question Paper

Unit
1.What is frequency response?
A frequency responses the steady state response of a system when the input to the system is a sinusoidal signal.

2.List out the various frequency domain specifications?
The frequency domain specification are
i)Resonant peak. ii)Resonant frequency.

3.Define –resonant Peak (mum r)?
The maximum value of the magnitude of closed loop transfer function is called resonant peak.

4.Define –Resonant frequency(mum f)?
The frequency at which resonant peak occurs is called resonant frequency.

5.What is bandwidth?
The bandwidth is the range of frequencies for which the system gain Is more than three dbB.The bandwidth is a measure of the ability of a feedback system to reproduce the input signal ,noise rejection characteristics and rise time.

6.Define Cut-off rate?
The slope of the log-magnitude curve near the cut-off is called cut-off rate. The cut-off rate shows the ability to distinguish the signal from noise.
7.Define –Gain Margin?
The gain margin,kg is described as the reciprocal of the magnitude of the open loop transfer function at phase cross over frequency.
Gain margin kg = one / omega G(j omega pc) omega.

8.Define Phase cross over?
The frequency at which, the phase of open loop transfer functions is called phase cross over frequency omega pc.

9.What is phase margin?
The phase margin ,omegais the amount of phase lag at the gain cross over frequency needed to bring system to the verge of instability.

11.Define Gain cross over?
The gain cross over frequency omega gc is the frequency at which the magnitude of the open loop transfer function is unity..

12.What is Bode plot?
The Bode plot is the frequency response plot of the transfer function of a system. A Bode plot consists of 2 graphs. 1 is the plot of magnitude of sinusoidal transfer function versus log omega.The other is a plot of the phase angle of a sinusoidal function versus log omega.

13.What are the main advantages of Bode plot?
The main advantages are:
i) Multiplication of magnitude can be in to addition.
ii) A simple method for sketching an approximate log curve is available.
iii) It is based on asymptotic approximation. Such approximation is sufficient if rough info on the frequency response characteristic is needed.
iv) The phase angle curves can be easily drawn if a template for the phase angle curve of 1+ j omega is available.



14.Define Corner frequency?
The frequency at which the 2 asymptotic meet in a magnitude plot is called corner frequency.

15.Define Phase lag and phase lead?
A negative phase angle is called phase lag.
A positive phase angle is called phase lead.

16.What are M circles?
The magnitude of closed loop transfer function with unit feed back can be shown to be in the for every value if M.These circles are called M circles.

Earning:   Approval pending.