Interview questions on Control System
- What is transfer function?
Ans: Transfer function is the ratio of the laplace transform of the output to the Laplace transform of the input at zero initial conditions. Transfer function=(laplace transform of o/p)/(laplace transform of i/p) at zero initial conditions.
- What is loop gain?
Ans: Loop gain is the product of all the branch gains in a loop. To find loop gain what we do is first find the loop whose gain is required to be found and then multiply all the transmittance of the branches present in the loop.
- What is Mason Gain formula?
Ans: Mason gain formula is required to find the transfer function from the signal flow graph. A complicated block diagram can be reduced to signal flow graph and from there we can find the transfer function using Mason gain formula.
Transfer function=(summation of product of all forward path gains and individual loop transmittance)/delta.
Delta=1-[sum of all individual loop transmittance]+[sum of loop transmittance product of two non touching loops in pairs]-[sum of product of triplets of non touching loops]+……..
- What is Damping Ratio?
Ans:It is the ratio of actual damping by critical damping and denoted by zeta.
Damping ratio=actual damping /critical damping.
- What is closed loop system?
Ans: Closed loop system is a type of control system in which apart from the forward path there is a closed loop feedback which helps to calibrate the input to achieve the desired value. It can have positive or negative feedback. Generally negative feedback is used.
- Under what condition system become unstable by routh hurwitz criteria?
Ans: Whenever there is a sign change in the first row of the routh Hurwitz the system becomes unstable also if a practical row becomes zero then also system becomes unstable.
- What is path gain?
Ans: The product of all the branch gains in a forward path gives us the path gain.
- Under what condition closed loop system become unstable and why?
Ans: When positive feedback is used in closed loop system it becomes unstable.
- What is signal flow graph?
Ans: Signal flow graph is the simplest representation of any block diagram of control system. It indicates the path and shows the details of the way the block diagram is connected.
- What do you mean by maximum overshoot?
Ans: The maximum positive deviation of the o/p with respect to the desired value is called maximum overshoot.