Control Systems Lab Viva Questions & Answers

Question No. 01: What is mathematical model of a control system?
Answer: Control system is a collection of physical elements connected together to serve an objective. The output and input relations of various physical systems are governed by differential equations. Mathematical model of a control system constitutes set of differential equations. The response of the output of the system can be studied by solving the differential equations for various input conditions.

Question No. 02: 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.

Question No. 03: 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.

Question No. 04: Explain Mechanical Translational System?
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.

Question No. 05: 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.

Question No. 06: 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

Question No. 07: 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.

Question No. 08: What are Test signals and their significance?
Answer: The knowledge of the input signal is required to predict the response of the system. In most of the systems input signals are not known ahead of the time and it is also difficult to express the input signals mathematically by simple equations. In such cases determining the performance of the system is not possible. Test signals helps in predicting the performance of the system as the input signals which we give are known hence we can see the output response of the system for a given input and can understand the behavior of the control system. The commonly used test signals are impulse, ramp, step signals and sinusoidal signals.

Question No. 09: 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 variables.

Question No. 10: What is S-domain and its significance?
Answer: By taking Laplace transform for differential equation in the time domain equations in S-domain can be obtained. L{F(t)}=F(s) S-domain is used for solving the time domain differential equations easily by applying the Laplace for the differential equations.

Question No. 11: 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
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