1. Process control is important for modern food processing industries to improve economics, ensure safety, reduce variation, waste, and maximize efficiency. 2. Accurate measurement of process parameters like temperature, pressure, and material levels is critical for control. Sensors can be penetrating, sampling, or nonpenetrating. 3. Control systems can be manual or automatic using control loops with sensors, controllers, and final control elements. The most common automatic controllers are on/off, proportional, proportional integral, and proportional integral derivative controllers.

1. Y.Bavaneethan.
Lecturer
Department of Food Technology
SLGTI. Sri Lanka.5/21/2019 Y.BAVANEETHAN. 1

2. Process control Hierarchy

3. Process control
• Process control is an integral part of modern food processing
industries;
process control is to improve the economics of the process
• Following objectives:
(1) Reduce variation in the product quality,
achieve more consistent production and maximise yield
(2) Ensure process and product safety
(3) Reduce manpower and enhance operator productivity
(4) Reduce waste
(5) Optimize energy efficiency.

4. • Processes are operated under either;
 steady state
- process conditions do not change
unsteady state conditions,
- process conditions depend on time
• Process control - requires control action in order to keep the
product within specifications.
• Many types of control actions and many different reasons for
controlling a process.
• Following two steps form the basis of any control action:
1. accurate measurement of process parameters.
2. manipulation of one or more process parameters using
control systems in order to alter or correct the process
behaviour.

5. Measurement of Process Parameters
Accurate measurement of the process parameters is absolutely
critical for controlling any process.
There are three main classes of sensors used for the
measurement of key processing parameters,
• temperature, pressure, mass, material level in containers,
flow rate, density, viscosity, moisture, fat content, protein
content, pH, size, colour, turbidity.
• Penetrating sensors: these sensors penetrate inside the
processing equipment and come into contact with the material
being processed.
• Sampling sensors: these sensors operate on samples which are
continuously withdrawn from the processing equipment.
• Nonpenetrating sensors: these sensors do not penetrate into the
processing equipment and, as a consequence, do not come into
contact with the materials being processed.

6. A well-designed control system has many benefits in the food industry:
• Energy savings – a well-controlled plant is energy efficient; poor
control is a major cause of excessive energy consumption.
• Consistent product quality – well-tuned control systems can
greatly reduce variation in food product quality to meet customer
specifications and reduce waste.
• Reduced manufacturing costs – good control systems can also
reduce manufacturing costs. They can diagnose faults at an early
stage in a process to ensure that product throughput and yield is
fully optimised.
• Better environmental performance – control systems can provide
early warning of loss of containment and excessive emissions.
• Safety improvement – control systems maintain safe conditions
and have built-in alarms to warn of deviations from the operational
plan

7. Control Systems
Control systems two main types:
• manual control
• automatic control.
Manual Control
In manual control, an operator periodically reads the process
parameter.
• when value changes from the set value manual process
required to control the operating process.
• control action necessary to drive the parameter towards the
set value.

9. Automatic Control
In automatic control, the process parameters measured by
various sensors and instrumentation may be controlled by using
control loops.
A typical control loop consists of three basic components:
• Sensor: the sensor senses or measures process parameters and
generates a measurement signal acceptable to the controller.
• Controller: the controller compares the measurement signal
with the set value and produces a control signal to counteract
any difference between the two signals.
• Final control element: the final control element receives the
control signal produced by the controller and adjusts or alters
the process by bringing the measured process property to
return to the set point,
- e.g. liquid flow can be controlled by changing the valve
setting or the pump speed.

10. Closed-loop Control System
Potato
Chips

11. An automatic control system can be classified into four main types:
• on/off (two position) controller
• proportional controller (P-controller)
• proportional integral controller (PI controller)
• proportional integral derivative controller (PID controller).
1. On/off (two position) controller
This is the simplest automatic controller for the final control
element.
• E.g => valve, is either completely open / at maximum, or
completely closed / at minimum.
There are no intermediate values or positions for the final control
element.
To protect the final control element, controllers are connected with
a dead band.
• The dead band is a zone bounded by an upper and a lower set
point.
• If measuring process parameter remains between these set
points,
no changes in the control system.

12.  On /Off controllers have three main advantages:
(1) low cost,
(2) Instant response and
(3) Ease of operation.
However, important of this controller is acceptable and
adjustable of upper and lower limit values for a specific
process.
The main disadvantages of this type of control action are:
(1) It is not suitable for controlling any process parameter likely
as large deviations from the set point.
(2) The quality of control is inferior to the continuous controller.

14. Process Control in Modern Food Processing
Control applications in food processing, three categories of
products:
(1) bulk commodity processing,
• E.g. grain milling, milk, edible oil, sugar and starch
production, where control is arguably most advanced,
(2) manufactured products,
• E.g. pasta, cheese, in-container and aseptically processed
products,
(3) products which have been subjected to processing methods,
• E.g. meat, fish, fruits and vegetables.
• Process control in food processing, that just attempting to control
single variables,
• e.g. level, temperature, flow, etc.,
- to systems which ensure smooth plant operation with timely
signalling of alarms.