Biological Control Systems - Short Questions and Answers - Mathankumar.S (VMKVEC)

BIOMEDICAL ENGINEERING – BCS – SHORT QUESTIONS AND ANSWERS
MATHANKUMAR.S, COORDINATOR/BME, V.M.K.V.E.C
BIOLOGICAL CONTROL SYSTEMS
UNIT-I: SYSTEM CONCEPTS
PART-A
1. Define system.
It is an arrangement of physical components related in such a manner as to form an
entire unit.
(or)
A group of elements or components are arranged in a sequence to perform a
specific function is called system.
2. List the types of control systems.
The two types of control system are open loop systems and closed loop systems.
3. Define Feedback.
The feedback is a control action, in which the output is sampled and a proportional
signal is given to input for automatic correction of any changes in desired output.
4. What is the purpose of feedback element?
It is the component required to generate the appropriate control signal applied to
the plant.
5. Give the important characteristics of open loop control system.
Their ability to perform accurately is determined by their calibration, which implies
to establish the input-output relation to obtain a desired system accuracy.
6. Distinguish between open loop & closed loop system.
S. No. Open Loop System Closed Loop System
1. Any change in output has no effect on the
input i.e. feedback does not exists.
Changes in output, affects on the
input which is possible by use of
feedback.
2. Output measurement is not required for
operation of system.
Output measurement is necessary.
3. Feedback element is absent. Feedback element is present.
4. Error detector is absent Error detector is necessary.
5. It is inaccurate & unreliable. Highly accurate & reliable.
6. Highly sensitive to the disturbance. Less sensitive to the disturbance.
7. Highly sensitive to the environmental
changes.
Less sensitive to the environmental
changes.
8. Bandwidth is small Bandwidth is large
9. Simple to construct and cheap. Complicated to design and hence
costly.
10. Generally are stable in nature. Stability is the major consideration
while designing.
11. Highly affected by nonlinearities. Reduced effect of nonlinearities.

7. Mention the types of feedback.
 Negative feedback
 Positive feedback.
8. Write the Mason’s gain formula.
Mason‟s gain formula states that the overall gain of the system as follows,
Overall gain,
T = T(s) = Transfer function of the system
K = Number of forward paths in the signal flow graph
Pk = Forward path gain of kth
forward path
Δ = 1 - [sum of individual loop gains] + [sum of gain product of all possible
combinations of two non-touching loops] – [sum of gain product of all possible
combinations of three non-touching loops] + ……………
Δk = Δ for that part of the graph which is not touching kth
forward path.
9. When will feedback exist in a system?
Feedback is said to exist in a system, when a closed sequence, of cause and effect
relations exist between systems available.
10.Define signal flow graph.
The graphical representation of the variables of a set of linear algebraic equations
representing the system is called signal flow graph.
(or)
A signal flow graph is a graphical representation of the relationship between
variables of a set of linear algebraic equations.
11.What are the basic properties of signal flow graph?
The basic properties of signal flow graph are
 Signal flow graph is applicable to linear system.
 It consists of nodes and branches. A node is a point representing a variable
or signal. A branch indicates functional dependence of one signal on the
other.
 A node adds the signals of the incoming branches and transmits this sum to
all outgoing branches.
 Signals travel along branches only in the marked direction and when it
travels its gets multiplied by the gain or transmittance of the branch.
 The algebraic equations must be in the form of cause and effect
relationship.
12.State non-touching loop.
The loops are said to be non – touching if they do not have common nodes.

13.Define transfer function of a system.
Transfer function of a given system is defined as the ratio of the Laplace
transform of output variable to Laplace transform of input variables at zero input
conditions.
14.What is the need for block diagram reduction?
Block diagrams of some of the control systems turn out to be complex. Such that
the evaluation of their performance requires simplification (or reduction) of block
diagrams which is carried out by block diagram rearrangements
15.Give the important features of feedback.
 Reduced effects of non-linearity‟s and distortion.
 Increased accuracy.
 Reduced sensitivity of the ratio of the output to input to variations in
system characteristics.
 Tendency toward oscillation or instability.
16.Mention a merit & a demerit of closed loop system.
The merits of closed loop system are:
 Accuracy of such system is always very high because controller modifies and
manipulates the actuating signal such that error in the system will be zero.
 Such systems sense environmental changes, as well as internal disturbances
and accordingly modify the error.
 In such system, there is reduced effect of non-linearity‟s and distortions.
The demerits of closed loop system are:
 Closed loop system is less stable than an open loop system.
 The overall gain of the system is reduced due to feedback.
17.Define block diagram.
A block diagram of a system is a pictorial representation of the functions
performed by each component of the system and shows the flow of signals.
18.What is transmittance?
The transmittance is the gain acquired by the signal when it travels from one
node to another node in signal flow graph.
19.What are the basic components of block diagram?
The basic components of block diagram are block (forward block & feedback
block), branch point, summing point and arrows.

20.List out the applications of control systems.
 Robotics
 Space – vehicle systems
 Aircraft autopilots and controls
 Ship and marine control systems
 Intercontinental missile guidance systems
 Automatic control systems for hydrofoils
 Surface – effect ships
 High speed rail systems including the magnetic levitation systems
UNIT II-TIME RESPONSE ANALYSIS OF CONTROL SYSTEMS
PART-A
1.What is the purpose of Laplace transform is used in control system?
The output of any control system, for any input can be obtained by solving integral
differential equations. Mathematically it is very difficult to solve such equations in
time domain. The Laplace transform of such integral differential equations converts
them into simple algebraic equations.
2.Define step signal.
It is the sudden application of the input at a specified time. Mathematically it can be
expressed as
R(t) = A for t > 0
R(t) = 0 for t< 0.
If A= 1, then it is called unit step function denoted by u(t)
3.List the steps involved in obtaining the transfer function.
 To write the differential equations governing the system.
 To Laplace transform the equations i.e. to replace the terms involving d/dt by s,
and integral of dt by 1/s.
 To obtain the ratio of transformed output to the input variables.
4.Name the properties of transfer functions.
The properties of transfer function are as follows:
 The transfer function of a system is the laplace transform of its impulse
response. i.e. if the input to a system with transfer function P(s) is an impulse
and all initial conditions are zero, the transform of the output is P(s).
 The roots of the denominator are the system poles and the roots of the
numerator are system zeros. The system stability can be described in terms of
the location of the roots of the transfer function.

5.Define time response.
The time response is the output of a closed loop system as a function of a time. It is
denoted by c(t). It is given by the inverse Laplace transform of the product of input
and transfer function of a system.
6.Define differential equations.
The basic models of dynamic physical systems are differential equations.
7.What is the purpose of standard test signals?
While analyzing the systems it is highly impossible to each one of it as a study the
response. Hence the analysis points of view, those signals, which are most commonly
used as reference inputs, are called as standard test signals.
8.Define ramp signal.
A ramp signal is a signal whose value increases linearly with time from an initial value
of zero at t=0.
Mathematically it can be expressed as
r(t) = At, for t ≥ 0
r(t) = 0, for t< 0.
If A= 1, then it is called unit ramp function.
9.What is an impulse signal?
A signal of very large magnitude which is available for very short duration is called
impulse signal. Ideal impulse signal is a unit impulse signal which is defined as a signal
having zero values at all time except at t=0. At t=0 the magnitude becomes infinite. It
is denoted by
10.State various time domain specifications.
The time domain specifications are:
 Delay time.
 Rise time.
 Settling time.
 Maximum over shoot.
 Peak time.
11.Define critical damping.
Critical damping provides the quickest approach to zero amplitude for a damped
oscillator. Critical damping occurs when the damping coefficient is equal to
the undamped resonant frequency of the oscillator.

12.What is meant by type number of the system? Give its significance.
The type number is given by number of poles of loop transfer function at the
origin. The type number of the system decides the steady state error.
13.Define damping ratio.
The damping ratio is defined as the ratio of actual damping to critical damping.
14.Define Damping.
Every system has the tendency to oppose the oscillatory behavior of the
system, which is called damping.
15.What is the difference between type and order of a system?
Type number of a system indicates the number of poles at the origin whereas
the order of the system indicates the order of the differential equation governing
the dynamics of a system.
16.Define response. Mention the test signals used to determine time
response.
The time response is the output of the closed loop system as a function of time. It
is denoted by c(t).
The commonly used test signals in control system are Impulse, Step, Ramp,
Acceleration and Sinusoidal signals.
17.What is transient and steady state response?
Transient state response:
The transient response is the response of the system when the input changes
from one state to another.
Steady state response:
The steady state response is the response as time, „t‟ approaches infinity.
18.Define rise time and settling time.
Rise time:
It is the time required for the response to rise from 0 – 100% for first time.
It is denoted as tr.
Settling time:
It is the time required for the response curve to stay with in tolerance band.
Normally 2% (or) 5% tolerance band are used. It is denoted as ts.

19.How the system is classified on the value of damping?
Depending on the value of damping, the system is classified into four cases:
Case 1: Undamped system, (damping ratio = 0)
Case 2: Under damped system (0<damping ratio <1)
Case 3: Critically damped system (damping ratio = 1)
Case 4: Over damped system (damping ratio > 1)
20.Define steady state error.
It is defined as difference of desired output to actual output as time tends to
unity.
UNIT III-THE CONCEPT OF STABILITY & ROOT LOCUS TECHNIQUE
PART-A
1.Define stable system.
To get the desired output, system must pass through transient period. Transient
response must vanish after some time to get the final value closer to the desired value.
Such systems in which transient response dies out after some time is called stable
systems.
(or)
A system is said to be stable, if every bounded input produces a bounded output.
2.What are the conditions for a linear time invariant system to be stable?
A linear time- invariant system is stable if the following two notions of system
stability are satisfied.
 When the system is by a bounded input, the output is bounded.
 In the absence of the input, the output tends towards zero irrespective of
initial conditions.
3.Define parameter variations.
The parameters of any control system cannot be constant through its entire
life. There are always changes in the parameters due to environmental changes and
other disturbances. These changes are called parameter variations.
4.State Routh criterion for stability.
Routh‟s criterion states that, the necessary and sufficient condition for the
stability is that, all the elements in the first column of the Routh‟s array be positive. If
the condition is not met, the system is unstable, and the number of sign changes in the

elements of the first column of Routh‟s array corresponds to the number of roots of
characteristic equation in the right half of the S-plane.
5.Define sensitivity of a control system.
An effect in the system performance due to parameter variations can be
studied mathematically defining the tern sensitivity of a control system. The change in
particular variable due to parameter can be expressed in terms of sensitivity.
6.What do you mean by asymptotic stability?
In the absence of the input, the output tends towards zero (the equilibrium
state of the systems) irrespective of initial conditions. This stability is known as
asymptotic stability.
7.Define BIBO stability.
A linear relaxed system is said to have BIBO stability if every bounded (finite)
input results in a bounded (finite) output.
8.What do you mean by root locus technique?
Root locus technique provides a graphical method of plotting the locus of the
roots in the S-plane as a given system parameter, is varied over the complete range of
values (may be from zero to infinity). The roots corresponding to a particular value of
the system parameter can then be located on the locus or the value of the parameter
for a desired root location can be determined from the locus.
(or)
Root locus technique is a powerful tool for adjusting the location of closed loop
poles to achieve the desired system performance by varying one or more system
parameters. It is a method of plotting the locus of the root of the characteristic
equation in S-plane when the gain of the system is varied over the entire range.
9.Define critically or marginally stable system.
A linear time invariant system is said to be critically or marginally stable, if for
a bounded input, its output oscillates with constant frequency and amplitude.
(or)
A system said to be marginally stable system, if its response to a bounded input
becomes a constant.
10.What is the necessary condition for stability?
The necessary condition for the stability is that all the co-efficient of the
characteristic polynomial be positive.

11. State Hurwitz criterion.
The necessary and sufficient conditions to have all roots of the characteristic
equation in left half of the s-plane is that, the sub-determinants DK, k = 1,2,…..,m
obtained from Hurwitz‟s determinant must be positive.
12.Define absolute stable.
Absolutely stable with respect to a parameter of the system, if it is stable for
all values of this parameter.
13.What do you mean by relative stability?
Relative stability is a quantitative measure of how fast the transients die out in
the system.
14.Give an application of Routh Stability criterion.
The Routh Stability criterion is frequently used for the determination of the
condition of stability of linear feedback control systems.
15.What is auxiliary polynomial?
In the construction of the Routh array, a row of all zero indicates the existence
of an even polynomial as a factor of the given characteristic equation. In an even
polynomial, the coefficients of auxiliary polynomial are given by the elements of the
row just above the row of all zeros.
16.How will you find the root locus on real axis?
To find the root locus on real axis, choose a test point on the real axis. If the
total number of poles and zeros on the real axis to the right of this test point is odd
number, then the test point lies on the root locus. If it is even number means, then the
test point does not lie on the root locus.
17.When a system is said to be limitedly stable?
For a bounded input signal, if the output has constant amplitude oscillations,
then the system may be stable or unstable, under some limited constraints. Such a
system is called limitedly stable system.
18.What is angle criterion of root locus?
The angle criterion of root locus states that S =Sa will be a point on root locus
if for that value of S, the argument or phase of G(S)H(S) is equal to an odd multiple of
180°.
19.How will you find the gain K at a point on the root locus?
The gain K at a point S= Sa on root locus is given by K= product of length of vectors
from open loop zero to the point Sa product of length of vectors from open loop poles
to the point Sa.

20.What are the dominating poles and zeros?
The poles of a system give rise to the longest lasting term in the transient
response of the system. Then those poles are called Dominating poles.
The zero which is closer to the origin than all over zeros is known as dominating
zero.
UNIT IV-FREQUENCY RESPONSE ANALYSIS
PART-A
1.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.
2.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.
3.What is cut-off rate?
The slope of the resultant magnitude curve near the cut-off frequency is called
cut-off rate.
4.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.
5.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.
6.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.

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 is resonant frequency?
The frequency at which the resonant peak occurs is called Resonant frequency.
The resonant peak is the maximum value of the magnitude of closed loop transfer
function.
9.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
10.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.
11.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.
12.What is approximate Bode plot?
In approx. bode plot the magnitude plot of first and second order factors are
approximated by two straight lines, which are asymptotes to exact plot. One straight
line is at 0db, for the frequency. For the frequency range 0 to ωc and the other

straight line is drawn with a slope of 20 db/dec for frequency range ωc of 10^(infinity).
Here ωc is corner frequency.
13.State Nyquist stability criterion.
If G(s)H(s) contour in the G(s)H(s) plane corresponding to Nyquist contour in s-
plane encircles the point -1+j0 in the anti-clockwise direction as many times as the
number of right half s-plane poles of G(s)H(s). Then the closed loop system is stable.
14.Define Bandwidth.
The Bandwidth is the range of frequencies for which the system gain is more than -
3db.
15.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
16.Give the limitations of frequency response analysis.
 The methods considered somewhat “old” and outdated in view of extensive
methods developed for digital computer simulation and modeling.
 Obtaining frequency response practically is fairly time consuming.
 For an existing system, obtaining frequency response is possible only if the time
constants are up to few minutes.
17.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 BW is increased damping
ratio and rise time both reduces.
18.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.

19.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
20.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 RHS of s-plane and encircle if any must be in
clockwise direction.
UNIT V-BIOMEDICAL APPLICATIONS
PART-A
1.Define periodic breathing.
Periodic breathing refers to the cyclic modulation of respiration that occurs
over the time-scale of several breaths. It does not commonly occur in normal during
wakefulness; however, its frequency of incidence increases dramatically during ascent
to altitude as well as during sleep onset.
2.What is ceyne stokes breathing?
An exaggerated form of periodic breathing known as ceyne stokes breathing. It
is frequently observed in patients with congestive heart failure.
3.Mention the function of endocrine.
The main function of endocrine glands is to secrete hormones directly into the
blood stream.
4.What is the purpose of pupillary light reflex?
The purpose of Pupillary Light Reflex is to regulate the total light flux reaching
the retina, although the same pupil control system is also used to alter the effective
lens aperture so as to reduce optical aberrations and increase depth of focus.
5.State cyclic neutropenia.
Cyclic Neutropenia is a disorder that causes frequent infection and other health
problems in affected individuals. People with this condition have recurrent episodes of
neutropenia during which there is a shortage of neutrophils.

6.What is the process of respiration?
Respiration is an essential and important process in all living organisms. It helps
in the exchange of gases and provides oxygen which is very important for the survival
of most of the life forms on earth.
7.Define Hormones.
Hormones are chemical substances that affect the activity of another part of
the body. In essence hormones serve as messengers, controlling and coordinating
activities throughout the body. It controls the function of entire organs.
8.State knee jerk reflex.
Knee jerk reflex is used in routine medical examinations as an assessment of the
state of the nervous system.
9.Define adaptive.
Adaptive means that the system may be able to offset any change in output not
only through the feedback but also by allowing the controller or plant characteristics
to change.
10.What is the function of lungs?
The process of the lungs are to bring oxygen into the body and to remove
carbondioxide. Oxygen is a gas that provides us energy, while carbondioxide is a waste
product or „exhaust‟ of the body.
11.Define endocrine.
The endocrine system is a collection of glands that produce hormones, that
regulate metabolism, growth and development, tissue function, sexual function,
reproduction, sleep and mood among other things.
12.What is occulomotor system?
The occulomotor system is the stabilization of the visual image on the retinae
during movement.
13.Define pupil.
The pupil is a hole located in the center of the iris of the eye that allows light
to strike the retina .It appears black because light rays entering the pupil are either
absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections
within the eye that mostly miss existing the narrow pupil.

14.State stretch reflex.
The stretch reflex is a muscle contraction in response to stretching within the
muscle. It is a monosynaptic reflex which provides automatic regulation of skeletal
muscle length. When a muscle lengthens, the muscle spindle is stretched and its nerve
activity increases.
15.Mention the function of Autonomic Nervous system.
The autonomic nervous system controls blood pressure, heart and breathing
rates, body temperature, digestion, metabolism (thus affecting body weight), the
balance of water and electrolytes (such as sodium and calcium), the production of body
fluids (saliva, sweat, and tears), urination, defecation, sexual response, and other
processes.
16.Define autonomic nervous system.
The autonomic nervous system is also known as visceral nervous system and
involuntary nervous system, is a division of the peripheral nervous system that
influences the function of internal organs. The autonomic nervous system is control
system that acts largely unconsciously and regulates the heart rate, digestion,
respiratory rate, papillary response, urination and sexual arousal.
17.What are proprioceptors?
In the limbs, the proprioceptors are sensors that provide information about
joint angle, muscle length, and muscle tension, which is integrated to give information
about the position of the limb in space.
18.Define muscle spindle.
The muscle spindle is one type of proprioceptor that provides information about
changes in muscle length. Muscle spindles are small sensory organs that are enclosed
within capsules. They are found throughout the body of the muscle, in parallel with
extra fusal fibers.
19.What is central nervous system?
The central nervous system (CNS) is the part of the nervous system consisting
of the brain and spinal cord. The central nervous system is so named because it
integrates information it receives from, and coordinates and influences the activity of,
all parts of the bodies of bilaterally symmetric animals.
20.Mention the function of Cardiovascular Control System.
The cardiovascular control system consists of the heart, blood vessels and
blood. This system has three main functions: Transport of nutrients, oxygen &
hormones to cells throughout the body and removal of metabolic wastes
(Carbondioxide, nitrogenous wastes).

Biological Control Systems - Short Questions and Answers - Mathankumar.S (VMKVEC)

More Related Content

What's hot (20)

Viewers also liked (7)

Similar to Biological Control Systems - Short Questions and Answers - Mathankumar.S (VMKVEC) (20)

More from Mathankumar S (20)

Recently uploaded (20)

Biological Control Systems - Short Questions and Answers - Mathankumar.S (VMKVEC)