Summary
Highlights
Commercial and industrial buildings heavily rely on automation for their mechanical and electrical systems, a trend that is continuously growing. This video will explore how these systems are controlled and what devices are used, with a special mention of Telecontrols, a leading manufacturer in automation since 1963.
A Programmable Logic Controller (PLC) is a small computer that executes pre-programmed outputs based on inputs and specific rules. These are used in commercial and industrial applications for system control with minimal or no manual intervention, ranging from simple on/off functions to sophisticated responses based on calculations and logic.
A PLC system consists of input modules (field sensors), a Central Processing Unit (CPU), and output modules (field output devices). Input modules detect signals (digital or analog) and convert them for the CPU. The CPU is the 'brain' storing the program and making decisions. Output modules provide signals to control devices like lights, valves, or motors. Other components include a battery, screen, time clock, and power supply.
The basic operation of a PLC involves an input scan (detecting input states), a program scan (determining actions), executing program logic, updating outputs, and performing housekeeping (diagnostics, communications). The 'scan time' varies based on the system's sensitivity and complexity of inputs.
A simple example illustrates a PLC controlling a boiler based on a bi-metallic strip temperature sensor. If the room is cold, the PLC activates the boiler. A key advantage of PLCs over simple relays is the ability to incorporate time functions, preventing the boiler from activating during unoccupied hours, and adding more complex logic such as motion sensors.
A more advanced example uses a thermistor and an actuator valve with a PID (Proportional Integral Derivative) control loop. Instead of simple on/off, the PID control modulates the valve's opening to precisely match heating demand, preventing overshoot and maintaining the desired room temperature efficiently.
A complex application involves a PLC with optimizer software for heating/cooling. This system learns building heat-up/cool-down rates and starts operations optimally before occupancy. It can also manage duty-standby pumps, monitor flow sensors for pump failures, and factor in external temperatures and schedules to ensure optimal conditions by a scheduled time.
The main advantages of PLCs include local storage of control software (ensuring operation even if a central system fails), software-based input/output connections (reducing physical wiring), smaller installation footprint, easier reprogramming, faster fault finding, ability to load programs onto multiple units, and expandability of inputs and outputs.
Before PLCs, control was managed by banks of relays, which were physically wired to control dedicated inputs and outputs. Changing operations required re-wiring, making them complex, vast, and difficult to troubleshoot. With the advent of solid-state electronics, these relay banks were replaced by software logic, making PLCs widely adopted.