control system

1. CONTROL SYSTEMS
Presented by
P GODIESWARI
M K GAYATHRI
V GULSHAN
R HARINI

2. system
Number of element or components are
connected in a sequence to perform the specific
function
Control system
➢ Output quantity is control by varying the input
quantity
➢ A control system consisting of interconnected
components is designed to achieve a desired
purpose
TYPE OF CONTRL SYSTEM
➢ Open loop system
➢ Closed loop system

3. Open loop system
Output has no effect
upon input quantity
Not automatically
correct the variation
in its output
Output not feedback
to input for correction
•Input
•R(t)
•Plant
•Or system
•Output
•C(t)

4. Closed loop system
➢ Output has effect upon
input quantity
➢ Automatically correct the
variation in its
output
➢ Output feedback to input
for correction
➢ It is also called as
automatic control system

5. Advantage
▪ Simple
▪ Economical
▪ Easy to construct
▪ stable
open loop system

6. Disadvantage
▪ Inaccurate
▪ Unreliable
▪ Change in output due to external
disturbances are not corrected
automatically
Open loop system

7. Advantage
▪ Accurate even the presence of
nonlinearities
▪ sensitivity
▪ Stable
▪ Less affected by noise
Closed loop system

8. Disadvantage
▪ complex
▪ costlier
▪ Reduce the gain of system more care to
design a stable closed loop system
Closed loop system

9. APPLICATION
Temperature control system

10. Traffic control system

11. Numerical control system

12. SERVOMOTORS

13. SERVOMOTORS
▪ WHAT IS SERVO MOTOR ?
▪ It is a special type of motor.
▪ Automatically operated up to certain limit
for a given command.
▪ It uses error sensing feedback to correct
the performance.

14. TYPES OF SERVO MOTORS
AC SERVOMOTORS
DC SERVOMOTORS
AC SERVOMOTORS
❑ Induction motor with
low (X/R) ratio.
❑ Consists of two main parts
as follows,
STATOR
❑ Two windings displaced by 90 degree.
▪ Reference winding constant AC supply.
▪ Control winding control voltage from servo
amplifier.

15. ROTOR
✓ It is classified into two types as follows
SQUIRREL CAGE ROTOR
✓ Use of aluminium reduces weight.
✓ Low inertia.
✓ Air gap is small.
✓ High resistance.
DRAG CUP ROTOR
✓ Two air gaps.
✓ Used in low power applications.
✓ Made up of aluminium.

16. WORKING
▪ The voltage applied to stator creates RMF which
makes rotor shaft to rotate.
▪ Torque-Speed characteristics.
✓ Linear for low (X/R) ratio.
✓ Non-linear for high (X/R) ratio.
▪ Linear characteristics depends
on control voltage.
▪ It is operated in low speed range.

17. AC SERVO MOTOR FEATURES
o Small (X/R) ratio & high efficiency.
o Smooth, Less weight & low cost.
o Robust construction & noise free working.
APPLICATIONS OF AC SERVO MOTORS
o Recorders,Computers and Robotics.
DC SERVOMOTORS
o It is classified as ,
o Electromagnetic field motor.
o Permanent motor.

18. ELETROMAGNETIC FIELD MOTORS
FIELD CONTROLLED MOTORS:-
▪ Field winding control signal.
▪ Armature winding constant current.
FEATURES
▪ Large time constant.
▪ Open loop system.
▪ Preferred for smaller
rate motors.

19. ARMATURE CONTROLLED DC
SERVO MOTORS
▪ Armature winding control signal.
▪ Field winding constant current source.
FEATURES
▪ Small time constant.
▪ Closed loop system.
▪ Preferred for large
rate motors.

20. PERMANENT MAGNET MOTORS
▪ Field winding Permanent magnet.
▪ Armature winding voltage.
FEATURES
▪ No field supply is required.
▪ Highly efficient.
▪ Less affected by
temperature rise.
▪ Less heating.

21. SYNCHROS

22. Synchros
Synchros is a name for a family of
inductive devices which works on the
principle of a rotating transformer.
They can be used in following two ways
1. To control the angular position of load from
a remote place.
2. For automatic correction of changes due to
disturbance in the angular position of the
load.

23. Synchro Transmitter
❑ When the rotor is
excited by ac voltage,
the rotor current flows,
and a magnetic field is
produced.
❑ The rotor magnetic
field induces an emf in
the stator coils by
transformer action.

24. ❖ The input to the synchro transmitter is
the angular position of its rotor shaft.
❖ By measuring and identifying the set of
voltages at the stator terminal

25. Synchro control Transformer
➢The generated emf of
the synchro is applied as
input to the stator coils
of control transformer.
➢ This emf can be
measured used to drive
a motor so that the
position of the load is
corrected.

26. Synchro as Error
Detector
▪ The synchro error detector is formed by
interconnection of a synchro transmitter and
synchro control transformer.
▪ Initially the shafts of transmitter and control
transformer are assumed to be in aligned
position.

27. Synchro control transformer
▪ The null position of a
control transformer in
a servo system is that
position of its rotor
for which the output
voltage on the rotor
winding is zero

28. SIGNAL FLOW GRAPH

29. Signal Flow Graphs
▪ Alternative to block diagram;
▪ Consists only branches (systems), and nodes
(signals)

30. How to convert a B.D to SFG

31. Mason’s Rule

32. Mason’s Rule - explained

33. Mason’s Rule - explained

34. Mason’s Rule - explained

35. Properties of signal flow graph
▪ Applicable to linear systems only.
▪ Algebraic equations in the form of cause and
effect relationship.
▪ Node represents the variable or signal.
▪ Branch indicates functional dependence.

36. THANK YOU