1. Module 1

2. Module 1
 Need for process control – mathematical model
of first – order level, pressure and thermal
processes – higher order process – interacting
and non-interacting systems – continuous and
batch process – self-regulation – servo and
regulator operation.
 Basic control actions – characteristics of on-off,
proportional, single-speed floating, integral and
derivative control modes – P+I, P+D and P+I+D
control modes – pneumatic and electronic
controllers to realize various control actions.

3. Introduction
PROCESS: An operation or series of operations on fluid or solid
materials during which the materials are placed in a more useful
state.
The objective of a process is to convert certain raw
materials into desired products using available sources of energy
in the most economical way.
CONTROL: means methods to force parameters in the
environment to have specific values.

4. PROCESS may be controlled by measuring a variable
representing the desired state of the product and automatically
adjusting one of the other variables of the process. A desired
quantity is kept at set point irrespective of external influences.
AUTOMATIC PROCESS CONTROL
is the maintenance of a desired value of a quantity or
conditions by measuring the existing value, comparing it to the
desired value and employing the difference to initiate action for
reducing this difference. This requires a feedback control system
which does not require human aid.

5. Areas - Process Control
1. Processing industries such as petroleum, chemical, steel,
power and food for the control of assembly operations,
work flow, heat treating and similar variables.
2. Goods manufacturers such as automobile parts,
refrigerators and electronic equipments like television sets,
radio etc. for the control of assembly operations, work flow,
heat treating and similar variables.
3. Transportation systems such as railways, airplanes, free
missiles and ships.
4. Power machines such as machine tools, compressors and
pumps, prime movers, and electric power supply units for
the control of position, speed and power.

6. Need for Process Control
 Increase in productivity (increase in quantity or number of
products): helps to increase the efficiency of both man and
machine.
 Improvement in quality of products by meeting the product
specifications overcoming operational constraints.
 Improvement in the consistency of product dimensions,
performance and length of service.
 Economical improvement by way of savings in processing raw
materials, savings in energy, effective utilization of capital and
human labour etc.
 Minimize/ suppress the influence of external disturbances on the
process.
 Ensure the stability of the process.
 Optimize the performance of the process.
 Meet environmental regulations.

9. Batch & Continuous Processes
Batch Process: A process in which the materials or work
are stationary at one physical location
while being treated.
Eg:

10. Batch Process
Advantages
 A variety of different products can be made using the plant.
 Slow reactions can be carried out.
 Can use reactants in any state including solids.
Disadvantages
 Risk of contamination if more than one than one product
made in reaction vessel.
 Expensive down time while reactor is being filled and
emptied.
 Larger workforce required.
 Can be difficult to control highly exothermic reactions.

11. Batch & Continuous Processes
Continuous Process: A process in which the materials or work
flows more or less continuously through a
plant apparatus while being
manufactured or treated.
Eg: Almost all chemical plant processes

12. Continuous Process
Advantages
 More cost effective if large quantities of the chemical are
being made.
 No expensive ‘down time’ when plant is not being used.
 Automated process requires less labour.
Disadvantages
 High capital cost of setting up the plant
 Costs rise if plant not operated continuously.

13. FACTOR CONTINUOUS BATCH
Cost of factory equipment High Low
Rate of production High Low
Shut-down times Rare Often
Workforce Few people Many people
needed needed
Ease of automation Relatively Relatively
easy difficult

14. Self Regulating Systems
 Some systems have the capability that is designed to
produce continuous balance.

16. Refer: Krishnaswamy/
Stephanopoulos
CSTR – Self Regulation

17. General Closed Loop System

18. Equation for Feedback

19. Servo & Regulator Operation
SERVO OPERATION
 Set point only changes ; disturbance does not
change
d(s) = 0
REGULATOR OPERATION
 Disturbance only changes ; set point does not
change
y SP(s) = 0

20. Process Characteristics
 Process Equation
 Process Load
 Transient
 Process Lag
 Self Regulation

21. Control System Parameters
 Error
 Variable Range
 Control Parameter Range
 Control Lag
 Dead Time
 Cycling
 Controller Modes
 Control Actions (Direct & Indirect)

22. CONTROLLER MODES
Discontinuous Control Modes
 2 position (ON/OFF control) mode
 Multi position mode
 Floating control mode
Continuous Control Modes
 Proportional Control
 Integral Control
 Derivative Control
Composite Control Modes
 PI
 PD
 PID

23. DISCONTINUOUS CONTROLLER MODES
1. Two-Position Mode (ON-OFF controller)

24. 1. Two-Position Mode (ON-OFF controller)

25. Electrical Two Position Controller

26. Pneumatic Two Position Controller

27. Two Position Controllers
APPLICATIONS
 Adapted to LARGE SCALE SYSTEMS with relatively
SLOW PROCESS rates.
Eg: AC in a Hall
Disadvantage: Oscillation

28. 2. Multi position Mode

29. 2. Multi position Mode
 Requires more complicated
Final Control element

30. 3. Floating
Control
Mode
(Single speed)
dp/dt = ±KF

31. 4. Multiple Speed Floating Control

32. Applications
 Well suited to self regulation processes with a very
small lag or dead time.

33. Continuous Controller Modes
Proportional Control Mode
 Also known as correspondence control, droop control
and modulating control.
 Control action is proportional to Error.
Kp = Proportional Gain(Proportional Sensitivity)
 Proportional Band is the range of error to cover the 0%
to 100% controller output.
PB = 100/Kp

34. Proportional Control Mode
p = Kpep +p0
p = Controller Out put (%)
ep = Error (%)
p0 = Controller output with no error (%)

35. Proportional Control Mode

36. Proportional Control Mode
OFFSET : Whenever a change in load occurs, the proportional
control mode produces a permanent residual error.
 This can be minimized
by a larger Kp
Application : used in
processes where large load
change are unlikely or with
moderate to small process
lag times.

37. Integral Control (Reset Action) Mode
 the value of manipulated variable is changed at a rate
proportional to the deviation.
 If deviation is doubled over a previous value, the final
control element is moved twice as fast; when CV at SP
the FCE remains stationary.
Controller output,
p0 = Controller O/P at t=0

38. Integral Control (Reset Action) Mode

39. Integral Control (Reset Action) Mode
 If the error is zero, the output stays fixed at a value to
what it was when the error went to zero.
 If the error is not zero, the output will begin to increase
or decrease at a rate of KI percent/ second for every
one percent error.
 Transfer Function of Integral Control is:
 Integral Windup

40. Integral Control (Reset Action) Mode
** Offset eliminated

41. Derivative Control Mode
 Controller output depends on rate of change of error.
 Also known as Anticipatory Control, Rate response or
lead component.
 The controller anticipates what the error will be in the
immediate future and applies action which is
proportional to current rate of change of error.

42. Derivative Control Mode

43. Derivative Control Mode
 Drawback: for a noisy response with almost zero error it
will compute large derivatives and thus large control
action, which is not needed.
 Not used alone.
 For zero or constant error, no control action.
 Transfer Function of Derivative mode:

44. COMPOSITE CONTROL MODE
PI Control
PD Control
PID Control

45. Proportional – Integral Control (PI)
pt(0) = Integral term value at t=0 (initial value)
One-to-one correspondence of the proportional
mode is available and the integral mode
eliminates the inherent offset.

46. Proportional – Integral Control (PI)

47. Proportional – Integral Control (PI)
Used in systems with frequent or large load
changes.
Disadvantage
o Because of the integration time, however, the process
must have relatively slow changes in load to prevent
oscillations induced by the integral overshoot.
o During start up of a batch process, the integral action
causes a considerable overshoot of the error and
output before settling to the operating point.

48. Proportional – Derivative Control (PD)
Disadvantage:
o It cannot eliminate offset of proportional control
Advantage:
 It can handle fast process load changes as long as the
load change offset error is acceptable.

49. Proportional – Derivative Control (PD)

50. Proportional – Integral - Derivative Control (PID)
(three mode controller)

51. Proportional – Integral - Derivative Control
(PID)

52. ELECTRONIC CONTROLLERS
TWO POSITION CONTROLLER

53. ELECTRONIC CONTROLLERS
FLOATING TYPE CONTROLLER

54. ELECTRONIC CONTROLLERS
PROPORTIONAL MODE CONTROLLER

55. ELECTRONIC CONTROLLERS
INTEGRAL MODE CONTROLLER

56. ELECTRONIC CONTROLLERS
DERIVATIVE MODE CONTROLLER

57. ELECTRONIC CONTROLLERS
PI MODE CONTROLLER

58. ELECTRONIC CONTROLLERS
PD MODE CONTROLLER

59. ELECTRONIC CONTROLLERS
PID MODE CONTROLLER

60. PNEUMATIC CONTROLLERS
PROPORTIONAL MODE CONTROLLER

61. PNEUMATIC CONTROLLERS
PI MODE CONTROLLER

62. PNEUMATIC CONTROLLERS
PD MODE CONTROLLER

63. PNEUMATIC CONTROLLERS
PID MODE CONTROLLER