Understanding PLCs and Building Automation Systems

Introduction

• Commercial buildings and industrial facilities increasingly rely on automation for mechanical and electrical systems.
• Sponsored by Telecontrols (leading manufacturer in the automation industry since 1963).
  • Compatible with every PLC, HMI, and controller, reducing PLC programming time and saving valuable storage.
  • Contact: sales@telecontrols.com or LinkedIn.

What is a PLC?

• PLC: Programmable Logic Controller.
  • Small computer that carries out pre-programmed outputs based on inputs and specific rules.
  • Minimal to zero manual intervention required.

Historical Background

• Pre-PLC: Control via banks of relays.
  • Each relay controlled dedicated inputs/outputs based on physical wiring.
  • Complex and vast in size, making it hard to change operations or find faults.
• Post-PLC: Solid-state electronics and microchips replaced relay banks with software logic.
  • Input, rules application, and output commands.

Applications and Examples

• Widely used in airports for baggage handling.
• Combines with relays to directly deal with automation tasks and communicate with PLCs.

Input Modules

• Types: Digital (on/off) and Analog (ranges like 0-100%).
  • Examples: Bimetallic temperature strips, motion sensors, float switches, control knobs.
• Tasks:
  • Sense when a signal is received.
  • Convert signal voltage to the correct format for the CPU.
  • Isolate PLC from input voltage/current fluctuations.
  • Send corrected signal to CPU.

CPU (Central Processing Unit)

• Brain of the PLC.
  • Microprocessor: Executes work based on inputs and logic.
  • Memory chip: Stores program, output history, faults, alarms.
  • Other integrated circuits: Modbus, LAN connections for remote communication.

Output Modules

• Sends signals to controlled devices (lights, solenoid valves, motor starters, etc.).
• Additional components:
  • Battery for power failures.
  • User interface screen.
  • Time clock and calendar.
  • Power supply.

Basic PLC Operation

• Steps: Input scan → Program scan → Execute logic → Update outputs → Housekeeping.
• Scan time affects performance, varies by application (e.g., water tank vs. room temperature control).

Example Scenarios

• Simple Boiler Control: Bimetallic strip temperature sensor, PLC, and boiler.
  • PLC controls boiler based on time and occupancy.
• Advanced Control with PID Loop: Thermistor, PLC, and actuator valve.
  • Gradual valve opening to proportionally control room temperature.
• Complex Building Heating: With optimizer software and pump configurations.
  • PLC calculates optimal start times based on occupancy, room temp, and outside temp.

Advantages of PLCs

• Local storage of control software; operates independently of building management systems.
• Software connections replace extensive physical wiring.
• Smaller installation footprint.
• Easier reprogramming and fault finding.
• Easily expandable with additional input/output cards.

Conclusion

• Further learning: Links to related videos on variable frequency drives, motor starters, solenoid valves, duty and standby pumps.
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