Ultimate PLC Guide: How a Programmable Logic Controller Works

Picture this. You’re the owner of a beverage manufacturing facility. It’s business as usual when all of a sudden your operations come to an abrupt halt because the bottling conveyor system fails without a clear cause. Every minute of downtime is costing you serious money as the maintenance team struggles to find out what happened.

If you don’t have the proper processes in place to find and address issues with core systems, this scenario is bound to happen, resulting in hours or even days of downtime. In this fast-paced sector, a system failure isn’t just indicative of downtime — it can be a potentially business-ruining hit to your reputation, revenue and ongoing operations. 

Fortunately, programmable logic controller (PLC) systems exist to prevent this scenario. Through the automation of critical processes and continuous monitoring of equipment, PLCs detect potential problems before they turn into expensive breakdowns and downtime. Follow along for everything you need to know about how PLCs can save your business from disaster through the power of industrial automation and equipment monitoring.

What Is a Programmable Logic Controller (PLC)?

A programmable logic controller is a device used to control a computer system in an industrial setting. PLCs typically serve as the base of a predictive maintenance strategy, monitoring analog inputs, such as temperature or CO2 sensors, to make decisions about related outputs like equipment efficiency, production lines and manufacturing processes. PLCs often warn maintenance teams about potential asset issues before major breakdowns occur.

Industrial business owners need a PLC for a variety of reasons, including to: 

• Automate core production processes
• Maximize efficiency 
• Ensure consistently reliable business operations 

These devices reduce the number of manual errors while improving safety and productivity levels through full industrial control over machinery and by making live changes in operations.

Different Types of PLCs

There are two main types of programmable logic controllers: compact and modular.

What Is a Compact PLC?

A compact PLC, also known as a fixed PLC, is an all-in-one device that includes everything you need like the power supply processor (CPU) and input/output connections within a single unit. 

This type of PLC saves space and is easy to install, making it an excellent choice for simple and efficient automation of smaller applications with one integrated system.

What Is a Modular PLC?

Unlike a compact PLC, a modular type consists of separate components, with its power supply, processing, IO modules and extension units assembled on one or multiple racks.

A modular PLC is flexible and scalable, making it simple for users to optimize and grow the control system as required. This device handles convoluted automation tasks through the integration of various modules like inputs and outputs or other specialized functions. It is ideal for large, expanding applications.

Core Components in Both Types of PLCs

Regardless of whether you choose a compact or modular PLC for your applications, both device-types will have the following core components:

• Input devices: Signals from sensors, switches and additional devices providing critical data about the system’s current processing state.
• Output devices: Signals sent to control devices such as lights, valves or motors to direct actions following the PLCs programmed procedures.
• Central processing units (CPUs): For executing the control program, processing input data and generating output signals for proper management of automated systems.
• Communications: Empower data exchange between the PLC and external devices/systems, allowing for systemic coordination, monitoring and control within automated processes.
• Human machine interfaces (HMIs): Provide users with real-time data and commands for monitoring, controlling and interacting with the automated system. 

Industries That Use PLC Systems

Any business in the industrial sector can benefit from using PLC systems to automate industrial processes. Here are popular industries that commonly use PLCs:

• Cement: PLCs regulate raw material handling, grinding processes and kilns to ensure consistent, cost-effective cement production.
• Glass: PLCs are used to control temperature, cut glass and shape processes for guaranteed precision and well-organized systems in glass production.
• HVAC: PLCs manage HVAC systems for controlled climate management and efficient use of energy.
• Oil and gas: PLCs control and monitor drilling, extracting and safety systems in real-time for smooth, continued operations and to ensure hazard-free conditions.
• Automotive: PLCs automate robotic welding, part installations and painting to enhance production speed and quality throughout the entire assembly line.
• Healthcare: PLCs manage critical infrastructure such as HVAC, diagnostic and sterilization equipment for reliability and precision across all healthcare facility systems.

Programmable Logic Controller Use-Case Example

Let’s take a look at a real-life PLC example to demonstrate the serious value this device can have for manufacturing businesses. Suppose you’re that beverage manufacturer from before that needs to automate its bottle filling process to improve efficiency and consistency while reducing labor costs and human error. 

PLC Setup Requirements

System setup involves the following:

• Conveyor system: Bottles are moved along a conveyor belt to the filling station.
• Filling stations: Several filling heads are positioned along the conveyor to fill the bottles with the beverage.
• Sensors: Sensors detect the presence of bottles at each filling station, the fill level and any potential issues like jammed bottles.
• Actuators: Valves and pumps are controlled to manage the flow of the beverage.

PLC Application Example

Once it is setup, here is how the PLC will work in this industrial application:

• Control logic programming: The PLC is programmed with the control logic for the entire filling process. It manages the operation and timers of the conveyor belt, the filling stations and the sensors. For example, when a bottle reaches the filling station, the PLC signals the filling head to activate and fill the bottle.
• Sensors integration: The PLC reads the inputs from sensors to ensure each bottle is correctly positioned and filled to the desired level.
• Actuator control: Based on the sensor inputs, the PLC controls the actuators to open or close valves and start or stop pumps. It adjusts the filling rates and ensures that each bottle receives the correct amount of beverage.
• Data logging and monitoring: The PLC can be configured to log data related to the filling process, such as the number of bottles filled, the volume dispensed and any errors encountered. This data can be used for quality control, troubleshooting and performance analysis.
• User interface: An HMI connected to the PLC allows operators to have supervisory control and visualization over the PLC work.

Benefits of Using a PLC

Clearly, a PLC can ensure continued operational efficiency. Here are the main benefits of integrating a PLC device into your core business systems:

• Consistency: Execute and repeat precise tasks consistently for stable, efficient production processes.
• Increased efficiency and productivity: Automate your most complex tasks to speed up operations while boosting organization-wide productivity and reducing manual intervention.
• Reliability: PLCs are highly reliable without the need for frequent downtime to keep operations functioning within even the most demanding industrial settings.
• Data collection: PLCs collect real-time data across business systems to monitor and analyze information to make more informed decisions. 

How to Maintain a PLC

Like any equipment, proper care is needed to keep your PLCs functioning properly. Take these steps to properly maintain your PLC:

1. Dust off any debris: Regularly sweep around the PLC to clear off dust and debris that could potentially cause overheating or negatively impact continued operations.
2. Change filters: Regularly replace air filters as needed to ensure appropriate ventilation and to prevent the buildup of dust with the PLC device.
3. Check modules for worn-out parts: Continuously monitor PLC modules for any signs of wear. Replace any faulty or damaged components to prevent system failures.
4. Backup data: Back up the PLC program and configuration data to ensure critical information isn’t lost if a system failure occurs. A CMMS like Coast can integrate the data into helpful maintenance reports for simplified tracking and the ongoing storage of PLC data.  
5. Monitor area surrounding the PLC: Ensure the devices’ surroundings are free of excessive moisture, heat and obstructions to maintain the recommended operating conditions and keep the PLC safe.

How Does a CMMS Help Maintain a PLC?

Like any equipment in your facility, a computerized maintenance management system (CMMS) like Coast makes it easy to schedule maintenance on programmable logic controllers with simplified digital work orders. 

The CMMS will alert maintenance technicians about their assigned work orders within the mobile app. From there, they will be able to record data within the app to make information accessible to organizational leaders who need analytics dashboards for informed decision-making.

By having a routine maintenance strategy in place, it will extend the lifespan of the PLC as well as the equipment that the PLCs are monitoring to maximize efficiency and reduce downtimes.