Process controlBy the end of the presentation you should be able to answer the

following questions:

Using examples, explain the different methodsof process control systemsUsing an example, describe how PLC and PIDwork

Examples of where process control takes place:

• Oil refining

• Chemical processing

• Car manufacture

• Temperature control industries e.g. refrigeration plants such as meat factories

• Paper mills

• Food & beverage industries

Process control methods

1. Batch process control

2. Continuous process control

3. Discrete process control

Batch process control

• Used in processes where there are specific amounts of raw materials that are combined together and mixed for a certain amount of time.

• Examples: Food processing such as ready made meals or Beverage processing such as coca-cola

Food Batch process control example:

• Ingredients are measured into a large vessel and mixed together for a fixed time at a fixed temperature.

• The computer controls:– The amount of each ingredient is added – The length of time for each stage – The temperature for each stage

Continuous process control

• Used in processes that appear unending• For example, where a process is

continuous such as the refining process for petroleum

• Or, where is it necessary to maintain the same low temperature continually such as a refrigeration plant that processes meat

• Used to produce very large quantities of a product

Discrete process control

• Used to produce specific items

• Known as an On/Off or Start/Stop process

• For example, in car manufacturing, a robot arm has 1 job and so it will repeat the same job on many cars. (Starting and stopping with every new car)

TASK: What is an Open loop system? What is a Closed loop system?

Closed Loop System: A control systems that carries on workingcontinuously, they don’t just stop after onedecision has been made.Open Loop System: Only looks at its input signal in order todecide what to do. It takes no account at allof what is happening to its output.

What controls these processes?

• Process control is overseen by:

• A Programmable logic controller (PLC), this is a type of computer or microcomputer

Programmable logic controller (PLC)

• A type of computer/microcomputer used for a single purpose

• Accepts analogue and digital inputs

• Uses a set of logic statement to compare input data with pre-set values

• Used where the pre-set values are constant such as refrigeration plant

The system/program used on the PLC computer/microcomputer:

Proportional integral derivative (PID)• Used with closed loop systems• This is when a variable such as a temperature is being

continually monitored using a sensor that is connected to the PLC (which compares the input with the pre-defined values)

• The PID is responsible for calculating the difference between the input and the pre-set value

• This is then used by the PLC to proportionally change the output to reach the pre-defined values

• The PID will continuously monitor the difference

Questions

1. Describe the purpose of a programmable logic controller.

2. Where are PLCs used in industry? 3. What role does the PID play in the PLC?4. What are the advantages of PLCs? 5. How have PLCs impacted on the workforce?

6. Then read the EWT article on the OLC & make notes

7. Print out your spreadsheet slide about the function given last lesson

Task

• Watch the videos on the OLC>Control Systems> Process Control

• Discuss and decide what methods of process is being used.

Embedded web technology(EWT)

• Developed by NASA• So that experiments in space could be conducted by

NASA staff anywhere in the world• It integrates microprocessors, input sensors, output

actuators and software needed to control these• Example: There is an oven that can be controlled

remotely from anywhere in the world. The embedded software can be accessed over the web and then used to control the over temperature

• Example: surgeons can monitor astronauts hearts from earth using EWT

Read the NASA article on the OLC>Unit 2> Control