Level 5 – Further Programmable Logic Controllers (PLCs)

HND Unit 42:    Unit code H/615/1510


Programmable Logic Controllers (PLCs) were invented by the American Richard (‘Dick’) Morley in 1969, to be used in the manufacture of cars. Prior to that date production lines had been controlled by a mass of hard-wired relays. Using programmable devices in their place meant that changes in production could be implemented much faster without the need to rewire control circuits.

The aim of this unit is to further develop students’ skills in the use of PLCs and their specific applications within engineering and manufacturing. Among the topics included in this unit are: device interface methods, PLC signal processing and communications with other devices, PLC programming methodology and alternative programmable control devices.

On successful completion of this unit students will be able to research the design, selection and use of PLCs as part of a larger system, programme a PLC to solve an industrial process problem for a given application and illustrate the alternative strategies for using other available types of programmable control devices.

Learning Outcomes

By the end of this unit students will be able to:

  1. Discuss the selection of a specific PLC for a given industrial application.
  2. Evaluate how PLCs exchange information and process signals with other devices.
  3. Design a PLC programme to solve an industrial process problem for a given application.
  4. Analyse alternative strategies using other types of programmable control devices in industrial applications.


PLC selection:
Common PLC industrial applications
Different PLC types, features and manufacturers
External input and output devices and modules: analogue and digital
PLC operational characteristics: speed, current, voltages, memory
PLC signal processing and communications with other devices:
Communication links and standards Networked bus systems
Supervisory Control and Data Acquisition (SCADA) systems and Human Machine Interfaces (HMIs)
PLC programming methodology:
Fundamentals of logic–ladder and function block diagrams
Number systems: Binary, Hexadecimal, Octal, BCD System input and output allocation data
PLC functions: registers, Analogue to Digital (AtoD), performing calculations, high-speed counters and timers
Program test and debug software functions
PLC simulations and fault-finding
Alternative programmable control devices:  
Micro-controllers and Industrial computers
Programmable device interface methods:
Relays and solid state relays Opto couplers
Opto isolators
Motor driver interface integrated circuits