This document provides an introduction to a course on Process Instrumentation and Control. It defines process control as dealing with mechanisms, architectures, and algorithms for controlling processes. Examples of controlled processes include controlling temperature with steam addition and maintaining fluid levels in tanks. The objectives of control are to maintain operational conditions, transition between conditions, and define key terminology like manipulated and disturbance inputs, control and output variables, and common control structures like SISO, MIMO, and PID controllers.

1. ICE401: PROCESS INSTRUMENTATION
AND CONTROL
Class 1: Need for Process Control &
Process Terminology
Dr. S. Meenatchisundaram
Email: meenasundar@gmail.com
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Jan – May 2015

2. Introduction:
Process control is a mixture between the statistics and engineering
discipline that deals with the mechanism, architectures, and
algorithms for controlling a process. Some examples of controlled
processes are:
Controlling the temperature of a water stream by controlling the
amount of steam added to the shell of a heat exchanger.
Operating a jacketed reactor isothermally by controlling the
mixture of cold water and steam that flows through the jacket of a
jacketed reactor.
Maintaining a set ratio of reactants to be added to a reactor by
controlling their flow rates.
Controlling the height of fluid in a tank to ensure that it does not
overflow.
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Jan – May 2015

3. Process Control Background:
The traditional role of process control in industrial operations was
to contribute to safety, minimized environmental impact, and
optimize processes by maintaining process variable near the
desired values.
Generally, anything that requires continuous monitoring of an
operation involve the role of a process engineer.
In years past the monitoring of these processes was done at the
unit and were maintained locally by operator and engineers.
Today many chemical / process plants have gone to full
automation, which means that engineers and operators are helped
by DCS that communicates with the instruments in the field.
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Jan – May 2015

4. Benefits of Process Control:
The benefits of controlling or automating process are in a number
of distinct area in the operation of a unit or chemical plant.
Safety of workers and the community around a plant is probably
concern number one or should be for most engineers as they
begin to design their processes.
Chemical plants have a great potential to do severe damage if
something goes wrong and it is inherent the setup of process
control to set boundaries on specific unit so that they don’t injure
or kill workers or individuals in the community.
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Jan – May 2015

5. Objectives of Control:
1. Maintain the process at the operational conditions and set
points:
Many processes should work at steady state conditions or in a
state in which it satisfies all the benefits for a company such as
budget, yield, safety, and other quality objectives.
In many real-life situations, a process may not always remain
static under these conditions and therefore can cause substantial
losses to the process.
One of the ways a process can wander away from these
conditions is by the system becoming unstable, meaning process
variables oscillate from its physical boundaries over a limited time
span.
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Jan – May 2015

6. Objectives of Control:
An example of this would be a water tank in a heating and cooling
process without any drainage and is being constantly filled with
water.
The water level in the tank will continue to rise and eventually
overflow.
This uncontrolled system can be controlled simply by adding
control valves and level sensors in the tank that can tell the
engineer or technician the level of water in the tank.
Another way a process can stray away from steady state
conditions can be due to various changes in the environmental
conditions, such as composition of a feed, temperature conditions,
or flow rate.
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Jan – May 2015

7. Objectives of Control:
2. Transition the process from one operational condition to
another:
In real-life situations, engineers may change the process
operational conditions for a variety of different reasons, such as
customer specifications or environment specifications.
Although, transitioning a process from one operational condition to
another can be detrimental to a process, it also can be beneficial
depending on the company and consumer demands.
Examples of why a process may be moved from one operational
set point to another:
1. Economics, 2. Product specifications, 3. Operational
constraints, 4. Environmental regulations, 5. Consumer /
Customer specifications, 6. Environmental regulations, 7. Safety
precautions.
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Jan – May 2015

8. Definitions and Terminology:
In controlling a process there exist two types of classes of variables.
1. Input Variable – This variable shows the effect of the
surroundings on the process. It normally refers to those factors
that influence the process. An example of this would be the flow
rate of the steam through a heat exchanger that would change the
amount of energy put into the process. There are effects of the
surrounding that are controllable and some that are not. These are
broken down into two types of inputs.
a. Manipulated inputs: variable in the surroundings can be
controlled by an operator or by a control system in place.
b. Disturbances: inputs that can not be controlled by an operator
or control system. There exist both measurable and
immeasurable disturbances.
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Jan – May 2015

9. Definitions and Terminology:
2. Output variable- Also known as the control variable. These are
the variables that are process outputs that effect the surroundings.
An example of this would be the amount of CO2 gas that comes
out of a combustion reaction. These variables may or may not be
measured.
As we consider a controls problem. We are able to look at two
major control structures.
1. Single input-Single Output (SISO) - for one control (output)
variable there exist one manipulate (input) variable that is used to
affect the process.
2. Multiple input-multiple output (MIMO) - There are several
control (output) variable that are affected by several manipulated
(input) variables used in a given process.
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Jan – May 2015

10. Definitions and Terminology:
Cascade: A control system with 2 or more controllers, a "Master" and
"Slave" loop. The output of the "Master" controller is the setpoint
for the "Slave" controller.
Dead Time: The amount of time it takes for a process to start
changing after a disturbance in the system.
Derivative Control: The "D" part of a PID controller. With derivative
action the controller output is proportional to the rate of change of
the process variable or error.
Error: In process controls, error is defined as: Error = setpoint -
process variable.
Integral Control: The "I" part of a PID controller. With integral action
the controller output is proportional to the amount and duration of
the error signal.
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Jan – May 2015

11. Definitions and Terminology:
PID Controller: PID controllers are designed to eliminate the need
for continuous operator attention. They are used to automatically
adjust system variables to reduce error and hold a process
variable close to the setpoint.
Error is defined above as the difference between setpoint and
process variable.
Proportional Control: The "P" part of a PID controller. With
proportional action the controller output is proportional to the
amount of the error signal.
Setpoint: The setpoint is where you would like a controlled process
variable to be.
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Jan – May 2015