Controllers are devices that maintain process variables at set points by receiving input data, comparing the data to programmed set points, and signaling corrective action if needed. Controllers perform mathematical functions to compare input data to set points and may perform complex calculations or simple addition/subtraction. Controllers receive input, perform calculations, and produce an output signal to regulate the process.

1. Submitted by
vivek mishra
1009020110

2. Most industrial processes require that certain variables such as flow,
temperature, level or pressure should remain at or near some reference value,
called SET POINT. The device that serves to maintain a process variable value
at the set point is called a CONTROLLER.
A Controller is a device that receives data from a measurement instrument,
compares that data to a programmed set point, and, if necessary, signals a
control element to take corrective action.
Controllers may perform complex mathematical functions to compare
Activities a set of data to setpoint or they may perform simple addition or
subtraction functions to make comparisons. Controllers always have an ability
to receive input, to perform a mathematical function with the input, and to
produce an output signal.

3.  Controllersterminology
 Types of controllers & differences
 problems

4.  Process controls
 Self-powered controls
 Pneumatic and electro-mechanical controls
 Electronic controls
 Direct digital control (DDC)

5.  Sensor
 Measures quantity of
interest
 Controller
 Interprets sensor data
 Controlled device
 Changes based on
controller

6. Direct Indirect
Closed Loop or Feedback Open Loop or Feedforward

7.  Process control is
a statistics and engineering discipline that
deals
with architectures, mechanisms and algorith
ms for maintaining the output of a
specific process within a desired range

8. CONTROL
VALVE
SET- + PID PROCESS
VARIABLE
_
POINT
r e CONTROLLER m c
e = r-b m=f(e) FCE
b
electrical Non-electrical
signal FEEDBACK
signal
TRANSDUCER
(Temp. , Pr. Etc.)
r = ref. Point / Set-point
b = feedback variable
e = error(actuating) signal
m= manipulated variable
c = controlled variable / Process variable
FCE= Final Control Element

9.  Set Point
 Desired sensor value
 Control Point
 Current sensor value
 Error or Offset
 Difference between control point and set point

10.  mainly three types
 Proportional
 PI
 PID

11. x A K (Tset point Tm easured)
x is controller output
A is controller output with no error
(often A=0)
K is proportional gain constant
e =is error (offset)

12.  Always have an offset
 But, require less tuning than other
controllers
 Very appropriate for things that change
slowly
 i.e. building internal temperature

13.  K/Ti is integral
gain
 If controller is
tuned properly,
offset is reduced to
zero

14.  Scheduling issues
 Require more tuning than for P
 But, no offset

15.  Improvement over PI because of faster
response and less deviation from offset
 Increases rate of error correction as errors get
larger

16. Proportional
(how much)
K d (Tset point Tmeasured)
x K (Tset point Tmeasured) (Tset point Tmeasured)d K Td
Ti d
Differential
Integral
howfast
(how long)
 For our example of heating

17.  PIDcontrol can be costly to implement and
support.
 It requires frequent valve- and damper-
position readjustment and this nearly
continuous repositioning shortens actuator
life, adds to maintenance costs, and makes
control stability a question.

18. Controller Response Overshoot Error
time
On-off Smallest Highest Large
Proportional Small Large Small
Integral Decreases Increases Zero
Derivative Increases Decreases Small
change

20. These controllers made the beginning in old generation
automatic process control. Today also these are
extensively used in industrial process controls due to
their inherent flame/explosion proof characteristics
as no electric currents are used/ generated.
Pneumatic Controllers come as Panel mounting type
and also field mounting type with weather proof
enclosures.
There are two basic components of pneumatic
controllers :
 Displacement sensing device (Flapper Nozzle system)
 Pneumatic Relays

21.  It's a displacer type pneumatic
detector which converts
displacement into a pressure
signal.
 The diameter of the orifice is
of the order of 0.25 mm & that
of nozzle is 0.625 mm.
 The nozzle diameter should be
larger than the orifice diameter

22.  It acts as the second
stage amplifier . It is
capable of handling a
large quantity of air
flow and is used to
increase the gain in
conjunction with a
flapper nozzle

23. ADVANTAGES OF PNEUMATIC CONTROLLER
 No fire hazard
DISADVANTAGES :
 Slow response
 Condensate in instrument air causes choking action of
the nozzle or relays.
 Not practicable to keep the actuator at a long
distance
 Leakage in tubing can cause problems

24.  Electroniccontroller use electric power to
actuate the final control element. These
types of controllers have a wide range of
applications in modern process industries.

26.  Digital control is a branch of control theory that
uses digital computers to act as system controllers.
Depending on the requirements, a digital control
system can take the form of a microcontroller to
an ASIC to a standard desktop computer. Since a
digital computer is a discrete system, the Laplace
transform is replaced with the Z-transform.

27.  Digital systems are more precise and more
extensible. They are usually able to work over much
longer distances as well. An example of extensibility
might be the ability to hook one up to the internet,
to extended event history recording, or for alerting
over pagers or cell phones.
Additionally, depending on the type of control
system, it may be less expensive to install and/or
maintain.