BIOMEDICAL ENGINEERING – BCS – UNIT II - SHORT QUESTIONS AND ANSWERS

MATHANKUMAR.S, COORDINATOR/BME, V.M.K.V.E.C

BIOMEDICAL CONTROL SYSTEMS

UNIT II-TIME RESPONSE ANALYSIS OF CONTROL SYSTEMS

PART-A

1. State the various standard test inputs used in control systems.

The standard test signals used in control systems are impulse, step, ramp, parabolic

and sinusoidal.

2. What is steady state error?

It is defined as difference of desired output to actual output as time tends to

unity.

3. 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)

4. What do you mean by time response of a control system?

The time response of a control system is the output of the system as a function of

time. It is given by inverse laplace transform of the product of input and system

transfer functions. The time response of a control system is the sum of the

transient response and steady state response.

5. 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.

6. List the time domain specifications.

The time domain specifications are:

Delay time.

Rise time.

Settling time.

Maximum over shoot.

Peak time.

BIOMEDICAL ENGINEERING – BCS – UNIT II - SHORT QUESTIONS AND ANSWERS

MATHANKUMAR.S, COORDINATOR/BME, V.M.K.V.E.C

7. What do you mean by a PID controller?

A PID controller is one in which the actuating signal consists of proportional error

signal added with derivative and integral of error signal.

8. Define critical damping.

If it is critically damped then it will return to closed as quickly as possible

without oscillating.

(or)

Critical damping provides the quickest approach to zero amplitude for a

damped oscillator.

9. 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.

10. Define damping and damping ratio.

Damping: Every system has the tendency to oppose the oscillatory behavior of

the system, which is called damping.

Damping ratio: The damping ratio is defined as the ratio of actual damping to

critical damping.

11. What are static error constants? What is their significance?

The position error constant (KP), the velocity error constant (Kv) and the acceleration

error constant (Ka) are called the static error constants. These constants are

associated with steady state error in particular type of system and for a standard

input. The error constant KP, Kv and Ka describe the ability of a system to reduce or

eliminate steady state errors.

12. Distinguish 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.

BIOMEDICAL ENGINEERING – BCS – UNIT II - SHORT QUESTIONS AND ANSWERS

MATHANKUMAR.S, COORDINATOR/BME, V.M.K.V.E.C

13. What is the effect of addition of a zero to the closed loop transfer

function?

In addition of a zero to the closed loop transfer function decreases the rise time

and increases the maximum peak overshoot of the step response.

14. Define response. Mention the test signals used to determine time

response.

The time response of a control system is the output of the system as a function of

time. It is given by inverse laplace of the product of input and system transfer

function of the system.

The common used test signals in time response are impulse, step, ramp, parabolic

and sinusoidal.

15. 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.

16. 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 within tolerance band.

Normally 2% (or) 5% tolerance band are used. It is denoted as ts.

17. What is the effect of a PD controller on the system performance?

The effect of a PD controller on the system performance is to increase the damping

ratio of the system and so the peak overshoot is reduced.

BIOMEDICAL ENGINEERING – BCS – UNIT II - SHORT QUESTIONS AND ANSWERS

MATHANKUMAR.S, COORDINATOR/BME, V.M.K.V.E.C

18. 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)

19. 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.

20. Write the transfer function of PD and PID controllers.

The transfer function of PD – controller, U(s)/E(s) = KP (1+ Td s)

Where, KP = Proportional gain

Td = Derivative time constant

The transfer function of PID – controller, U(s)/E(s) = KP [1+1/ Ti s +Td s)

Where, KP = Proportional gain

Ti = Integral time constant

Td = Derivative time constant