Electrical Question:
What are the Characteristics of Negative
Feedback?
Answer:
Negative Feedback in a Control System has
following Characteristics
Reduction in the gain at the expense of better
stability of the system
Rejection of disturbance signals in the system
Low Sensitivity to parameter variations
Accuracy in tracking the steady state value
What are the basic components of the
feedback control system?
Answer: Basic components of the feedback
control system are process system (open loop
system), feedback path element, error detector,
and controller.
Define Transfer Function?
Answer: Transfer Function of a control system
is defined as:
i) Ratio of Laplace transform of Output to the
Laplace transform of the Input with zero initial
conditions
ii) Transfer function is defined as the Laplace
transform of Impulse response of the system
with zero initial conditions
What is Time Invariant system?
Answer: Time Invariant System is one in which
the input and output characteristics of the
system does not change with time.
When Proportional (P) Controller is Used:
Proportional (P) Controller is used during the
following conditions:
Load Changes are small
Offset (error exist due to difference between
steady state value and desired value) can
be tolerated
The process reaction rate is such as to
permit a narrow proportional band. Since
this reduces the amount of the offset
When Integral (I) Controller is Used:
Integral (I) controller is used during:


When the offset must be eliminated
Integral saturation due to sustained
deviation is not objectionable
When Derivative (D) Controller is used:


Large transfer or distance velocity lags are
present
It is necessary to minimize the amount of
deviation caused by the system changes
When Proportional plus Integral (PI)
Controller is used:
Proportional and Integral action is employed
when



System changes is small
Offset must be eliminated
No objection on the recovery duration

What is Signal Flow Graph?
Answer: A Signal Flow Graph is a diagram
that represents a set of simultaneous linear
algebraic equations. By taking Laplace
transform the time domain differential
equations governing a control system can
be transferred to a set of algebraic
equations in s-domain. The signal Flow
graph of the system can be constructed
using these equations.
What are the basic properties of Signal Flow
Graph?
Answer: The basic properties of the signal flow
graph are:





Signal Flow Graphs are applicable to linear
systems
It consists of nodes and branches. A node is
a point representing a variable or signal. A
branch indicates the functional dependence
of one signal on another
A node adds the signals of all incoming
branches and transmits this sum to all
outgoing branches
Signals travel along branches only in a
marked direction and is multiplied by the
gain of the branch
The algebraic equations must be in the form
of cause and effect relationship
Define Transfer Function?
Answer: Transfer Function of a control system
is defined as:
i) Ratio of Laplace transform of Output to
the Laplace transform of the Input with zero
initial conditions
ii) Transfer function is defined as the
Laplace transform of Impulse response of
the system with zero initial conditions
Where Servomechanism is used?
Answer: Servomechanism is used in control
system where the output is pertained to vary
the mechanical position of a device.
Servo Mechanism is widely used in
Governor Value position control mechanism
used in the power plants where speed of the
turbine is taken and processed using the
transducers and final control element is
brought as mechanical movement of the
value. Now a day’s Governor value control
is done with Electronic controls using power
Thyristors. Servomechanism is also widely
used in the robotic hand movement
What is the basic rule for Block Diagram
Reduction
Technique?
Answer:
The rules of the Block Diagram reduction
Techniques are designed in such a manner that
any modifications made in the diagram will not
alter the input and output relation of the system
Where Servomechanism is used?
Answer: Servomechanism is used in control
system where the output is pertained to vary
the mechanical position of a device.
Servo Mechanism is widely used in Governor
Value position control mechanism used in the
power plants where speed of the turbine is
taken and processed using the transducers
and final control element is brought as
mechanical movement of the value. Now a
day’s Governor Value control is done with
Electronic controls using power Thyristors.
Servomechanism is also widely used in the
robotic hand movements
1. What is Order of the system?
Answer: Order of the system is defined as the
order of the differential equation governing the
system. Order of the system can be determined
from the transfer function of the system. Also
the order of the system helps in understanding
the number of poles of the transfer function. For
nth order system for a particular transfer
function contains 'n' number of poles.
2. What is Time response of the control
system?
Answer: Time response of the control system is
defined as the output of the closed loop system
as a function of time. Time response of the
system can be obtained by solving the
differential equations governing the system or
time response of the system can also be
obtained by transfer function of the system.
3. How Time response of the system is
divided?
Answer: Time response of the system consists
of two parts: 1.Transient state response 2.
Steady state response. Transient response of
the system explains about the response of the
system when the input changes from one state
to the other. Steady state response of the
system shows the response as the time t,
approaches infinity.
Electrical Question: Explain
Translational System?
Mechanical
Answer: Model of mechanical translational
system can be obtained by using three basic
elements Mass, spring and Dash-pot.


Weight
the
mechanical
system
is
represented by mass and is assumed to be
concentrated at the center of body
The elastic deformation of the body can be
represented by the spring


Friction existing in a mechanical system can
be represented by dash-pot.
5. What is Pole of the system?
Answer: Pole of a function F(s) is the value at
which the function F(s) becomes infinite, where
F(s) is a function of the complex variable s.

6. What is Zero of the system?
Answer: Zero of a function F(s) is a value at
which the function F(s) becomes zero,
where F(s) is a function of complex variable
s.
1. What is Order of the system?
Answer: Order of the system is defined as the
order of the differential equation governing the
system. Order of the system can be determined
from the transfer function of the system. Also
the order of the system helps in understanding
the number of poles of the transfer function. For
nth order system for a particular transfer
function contains 'n' number of poles.
2. What is Time response of the control
system?
Answer: Time response of the control system is
defined as the output of the closed loop system
as a function of time. Time response of the
system can be obtained by solving the
differential equations governing the system or
time response of the system can also be
obtained by transfer function of the system.
3. How Time response of the system is
divided?
Answer: Time response of the system consists
of two parts: 1.Transient state response 2.
Steady state response. Transient response of
the system explains about the response of the
system when the input changes from one state
to the other. Steady state response of the
system shows the response as the time t,
approaches infinity
What is resonant peak?
Answer: Resonant peak is defined as the
maximum value of the closed loop transfer
function. A large resonant peak corresponds to
large overshoot in the transient response
What is Resonant Frequency?
Answer: The frequency at which resonant peak
occurs is called the resonant frequency.
Resonance frequency explains about the speed
of the transient response.
What is Cut-off rate?
Answer: The slope of the log-magnitude curve
near the cut-off frequency is called the cut-off
rate. The cut-off rate indicates the ability of the
system to distinguish between the signal and
the noise.
What is Phase cross over frequency?
Answer: The frequency at which the phase of
the open loop transfer function is 180o is called
the
phase
cross
over
frequency.
What is Gain Margin?
Answer: The Gain Margin is defined as the
reciprocal of the magnitude of open loop
transfer function at phase cross over frequency.
The gain margin indicates the amount by which
the gain of the system can be increased without
affecting the stability of the system.
Phase Margin?
Answer: The phase margin is the amount of
additional phase lag at the gain cross over
frequency required to bring the system to the
verge of instability.