PLC Fundamentals for Maintenance Engineers

By the end of the PLC Fundamentals curriculum, learners will be able to:

• Identify and explain the function of common industrial control panel components, including push buttons, selector switches, relays, motors, indicator lights, and sensors.
• Demonstrate correct wiring and testing of both digital and analogue input and output devices to a Siemens PLC and HMI.
• Apply safe working practices by using isolation devices, emergency stops, and status indicators during system operation.
• Distinguish between digital and analogue signals, explain how PLCs process each type, and apply scaling to interpret sensor values.
• Monitor and interpret PLC and HMI feedback, including I/O activity, fault states, and process conditions, to support troubleshooting.
• Understand how PLC logic controls outputs, including sequencing, latching, and PWM motor speed control.
• Follow structured worksheets to build practical confidence in tracing signals, testing circuits, and verifying safe system operation.
• Describe how a PLC processes basic on/off inputs to control outputs, using push buttons and indicator LEDs.
• Explain sequencing and latching logic, and demonstrate how a PLC can manage multi-step processes with start/stop conditions.
• Interpret HMI displays to monitor live I/O states, process steps, and alarms, and explain their role in operator interaction.
• Demonstrate safe isolation using a dual-channel emergency stop and reset circuit, and explain its role in industrial safety.
• Recognise how system status indicators show healthy, fault, and stop states, and explain their use in diagnostics.
• Distinguish between normally open (NO) and normally closed (NC) inputs, interpret their states on the HMI, and explain why both are used in control circuits.
• Connect and test an inductive proximity sensor, and describe its application in detecting objects and ensuring safe operation.
• Use a potentiometer to generate a 0–10 V analogue signal, and explain how PLCs scale and process analogue inputs.
• Measure and interpret readings from a PT100 RTD with transmitter, and explain how analogue scaling converts raw values into real temperatures.
• Operate PLC-driven outputs such as LEDs, relays, and motors, and explain how digital logic activates actuators.
• Demonstrate how PWM control varies motor speed, and relate duty cycle percentage to motor performance.
• Explain and test the function of relays in isolating PLC outputs from loads, and describe their importance in industrial control circuits.