What Is a Programmable Logic Controller (PLC)?
Answered September 16 2020
In this day and age, we’ve known computers to be high-tech devices capable of immensely complex computing power. Computers commonly refer to some of our most prized personal possessions, such as laptops, desktops, and handheld gadgets. However, for their most basic purpose, computers are fundamentally machines that operate using a precisely logical process. For industrial applications, computers more commonly come in the form of what are known as programmable logic controllers.
What Is a PLC?
A programmable logic controller, PLC for short, is the brain of a modern-day facility that depends on various machines and equipment. PLCs are small computers designed for heavy-duty industrial applications. Their rugged design allows them to thrive even in the harsh conditions of industrial operations. While relatively simple, PLCs are capable of applying programmable logical rules to automate processes and functions of plant equipment.
Before PLCs, relays were the only available way to control machines. Relays would energize and de-energize, in turn switching a component on or off. While this was a viable solution for one, two, or a few pieces of equipment, relay systems did not scale well with the size of operations. Control systems were a nightmare to design, maintain, and troubleshoot, as the number of components increased. PLCs revolutionized the way machines were controlled by offering computer-like capabilities while being competitively priced compared to the relay alternative at the time.
PLCs can generally fall into one of two general types:
1. Compact PLC
A compact PLC has a fixed number of input and output capabilities set by the manufacturer. These are generally appropriate for small-scale applications.
2. Modular PLC
A modular PLC, as the name implies, consists of individual modules or units that can more easily expand as needed. It offers additional flexibility in terms of capacity, which makes it advantageous for larger-scale operations.
How does a Programmable Logic Controller work?
A PLC takes in data through input modules, processes the information it gathers, and finally transmits its calculated outputs. Depending on the requirements of the plant, as well as the availability of inputs, PLCs can check for specific conditions to trigger corresponding actions.
The following are some key features of PLCs that allow them to perform the required tasks effectively.
A Programmable Logic Controller needs to gather information before it can even start processing any data. There are two main sources of inputs: those that come from equipment readings and those that are human-facilitated. Input modules connect the PLC with devices on equipment such as sensors, level detectors, and other measuring instruments. These input modules can also connect with human-facilitated inputs such as button pushes, switches, and dials.
After processing data, a PLC needs to translate its results to corresponding external actions for the linked equipment. Output modules connect the PLC to output devices such as relays, lights, valves, and other components.
Central Processing Units
Central processing units, or CPUs, act as the brain of a PLC. They read and interpret the input data to produce results and commands that come out of the output modules as signals.
In modern control systems, PLCs are components of a larger network of devices. Aside from the connections internal to the PLC itself, external connections to other components allow data to be more readily transmittable. For such applications, communication protocols must be in place to ensure that PLCs can send data to other systems.
In most cases, operators and facility staff require the information that is being processed by the PLCs. Human-machine interfaces (HMIs) should be in place to translate information within the processing units to an understandable form. HMIs can take the form of a display panel or simple status indicators.
These features of a PLC typically interact and operate in cycles. The user defines the required tasks through the programmable logic of the PLC. A typical step-by-step process may resemble the following:
- The PLC checks the status of the input modules and any connected devices.
- The CPU takes in the inputs then executes the logic defined by the user through the program.
- The output modules of the PLC send the signal to perform physical actions to the attached devices. Typical output commands would be to switch on or off, increase or decrease speed, and the like.
- The PLC runs an overall check to report the operating conditions of the attached devices. At this point, the PLC executes communication protocols to send out data to another system or some HMI.
- The PLC either ends or restarts the process as defined by the program.
What Is the Difference Between a PLC and SCADA?
SCADA stands for Supervisory Control and Data Acquisition. SCADA is generally a software system used to monitor various aspects of a plant facility and its components. It also allows the user to enter configured commands that translate to equipment actions. In simpler terms, SCADA acts as an overall control system that allows manipulation of both software and hardware elements.
In contrast, PLCs are generally hardware systems that directly link to power up machines, motors, and other equipment. With modified communication features, PLCs are also used to gather data from the equipment they control.
Together, PLC and SCADA systems allow users more control and flexibility over the whole facility. Imagine each machine to be controlled by a PLC, with potentially multiple PLCs across the facility. Further, you can suppose that all PLCs consolidate into a comprehensive view through SCADA. Not only does the user have full visibility of operations, but also total virtual control over the plant. With proper data communication in place, SCADA and PLC systems are constructive tools to implement a predictive approach in maintenance.
PLCs are some of the most adaptable products that have been in use for the past couple of decades across various industries. Apart from their practical and affordable design, PLCs are easily able to integrate with more recent innovations in technology such as SCADA.
Latest Maintenance Articles
- What Are Ideal Preventive Maintenance Schedules for Manufacturing Equipment?Root Cause Analysis Techniques and FundamentalsHow to Use eBay to Save Money and Time on ProcurementThe Ultimate Guide to Programmable Logic Controllers (PLCs)How to Respond to an FDA Warning LetterWhat Is Maintenance Process Mapping?
Fleet Management and GPS
Oil & Gas
Asset Management Questions & Answers
The Ultimate Guide to Programmable Logic Controllers (PLCs)
A programmable logic controller (PLC) works to control a computer system in an industrial organization. Here's everything you wanted to know about them.
How to Create a PLC Maintenance Checklist
Establishing a regular PLC maintenance checklist can minimize or eliminate downtime by discovering potential issues before they cause problems.
What Are the Risks and Benefits of Using a PLC?
While PLCs have been around for a long time, there are still some significant PLC risks that must be considered before implementation.
What Are the Best Tips for PLC Maintenance?
Given that PLCs (programmable logic controllers) are integral to many industrial operations, it’s important to keep an eye on PLC maintenance.
How Are Companies Using PLCs?
A programmable logic controller (PLC) monitors a specified set of inputs on a piece of industrial equipment and then makes output-related decisions.
What Is the Return on Investment for Predictive Maintenance?
To get a better idea of what the ROI for predictive maintenance could be in your facility, let’s take a look at a few real-world examples.
Predictive maintenance in agriculture
We cover the ways you can use IIoT to optimize soil cultivation, crop growth, livestock raising, and their related processes.
Predictive Maintenance in the Food Industry
The high upfront costs of implementing new maintenance methodologies can be difficult, but predictive maintenance can actually help.
Pressure Sensors: Types, Use Cases, and Definition
A pressure sensor is a device that senses and measures pressure. Pressure in this case, is defined as the amount of force exerted over an area.
What’s The Difference Between Sensors and Actuators?
Whereas sensors monitor conditions of equipment, actuators drive events within equipment. They ensure systems are functioning effectively.
6 Types of Temperature Sensors Defined and Use Cases
Temperature sensors are devices on machinery that track ambient temperatures, assess readings, and measure the impact of heat conditions
IoT Manufacturing: How IoT in Manufacturing Will Benefit Future Workplaces
IoT holds an especially significant place in manufacturing, with value estimates reaching up to $3.7 trillion in factories alone by 2025.
The 6 Sensors for Predictive Maintenance That Optimize Repair Timelines
Today, predictive maintenance relies on sensors in three major areas: early fault detection, failure detection, and CMMS integration.
How Does a Voltage Sensor Work? Definition and Common Uses
Voltage sensors are wireless tools that can be attached to any number of assets, machinery or equipment for monitoring purposes.
Industrial IoT Sensors: What Are They and Which Businesses Use Them
Industrial IoT sensors are widely used in different industries to monitor equipment, assets, systems, and overall performance.
IoT use Cases (Internet of Things) for Commercial and Industrial Business
Internet of Things technology is becoming increasingly prevalent throughout homes and businesses alike in numerous applications.
What Is a Vibration Sensor: How to Measure Vibration to Minimize Failures
Vibration sensors can be used to give maintenance teams insight into conditions within assets that might lead to equipment failure.
Failure Prediction Machine Learning: Using Machine Learning to Find Failures Before They Occur
Failure prediction machine learning is the application of artificial intelligence within the maintenance arena. This allows you to monitor your assets.
How do sensors and actuators work together?
When working in tandem within a given system, actuators receive signals from sensors and perform some kind of task based on that input.
What industries can use IIoT sensors?
Any industry that uses or maintains equipment can make use of IIoT sensors. A few of them include agriculture, manufacturing, and retail.
How are sensors used in predictive maintenance?
Predictive maintenance (PdM) typically uses data from sensors that monitor various conditions on equipment. Algorithms analyze data to predict maintenance.
What are the up and coming IIoT projects in the near future?
The most exciting IIoT projects on the horizon are for maintenance and training tasks and improving energy management with AR.
What do I need to get started for a predictive maintenance (PdM) program?
We talk a lot about planning in implementing maintenance strategies, and predictive maintenance (PdM) programs are no different.
How can my facility use acoustic analysis?
Acoustic analysis has fewer applications than PdM-tool vibration analysis, but what it lacks in breadth of application it makes up for in effectiveness.
What are some industry use cases for vibration analysis?
Amongst the tools in the predictive maintenance (PdM) toolkit, vibration analysis sees tons of use because of its extremely wide variety of applications.
What are the best IIoT projects to start with?
The best Industrial IIoT projects to start with are small ones that meet a specific business need. Once successful, you can increase the size and scope.
How much does deploying IIoT at my business cost?
Industry experts say that deploying an Industrial Internet of Things (IIoT) will cost a minimum of $50,000 or roughly 10 percent of your information technology budget over three years.
What are the benefits of IIoT?
Early implementers of the Industrial Internet of Things (IIoT) have reported better protection of assets, and raised levels of reliability and performance.
What are barriers to IIoT adoption?
The top five barriers to IIoT adoption are cybersecurity issues, a lack of standardization, an installed legacy system, high upfront investment, and a lack of skilled workers
What is prescriptive maintenance and how does it differ from predictive maintenance?
Prescriptive maintenance, is a maintenance concept that analyzes an equipment’s condition to create specialized recommendations to reduce operational risks.
What’s the easiest way to start a predictive maintenance program?
Start with your most critical piece of equipment, track information related to failures, and set up alerts to generate work orders to prevent breakdowns.
What are the biggest problems IIoT could solve for maintenance departments?
Each of these challenges can be alleviated through proper application of IIoT technology, so let’s run through each one starting from helping managing cost.
Will Industrial Internet of Things (IIoT) replace SCADA?
If it does happen, it will probably take a long while, mainly because it would involve uprooting one well-established system in favor of installing another.
What is machine learning and how does machine learning work with predictive maintenance?
Machine learning allows for more intelligent ways of processing data to predict when an asset will require maintenance.
What is the difference between Industry 3.0 and Industry 4.0?
In terms of the words themselves, Industry 4.0 refers to the fourth industrial revolution. The term was coined in 2011 to represent the role that cyber-physical systems (CPS), cloud computing, and IIoT (industrial internet of things) will have on manufacturing processes.
How do I incorporate predictive maintenance without sensors?
Almost by definition, predictive maintenance uses sensors, but the core principle of PdM doesn’t necessarily depend on them.
What are common use cases for using a mileage sensor in predictive maintenance?
If your business maintains a fleet of vehicles, you’ll want to use mileage sensors to trigger regular inspections, fluid changes, and replacements.
What are common use cases for using a voltage sensor in predictive maintenance?
One use case is power failure detection which can create significant downtime losses, and immediate notification can help minimize larger problems.
How do I select assets for predictive maintenance?
Choosing assets for predictive maintenance is a matter of priority, especially starting out. A few of the factors you’ll want to look at include:
What are the most common types of IIoT sensors available?
Dozens of sensors are already available to monitor, track, and report on critical aspects of your operations with more under development each day.
What are common use cases for using a vibration sensor in predictive maintenance?
Vibration often signals a potential problem within production facilities that can result in future breakdowns or shorter equipment lifespans.
What are common use cases for using a pressure sensor in predictive maintenance?
Pressure sensors alert maintenance teams when the pressure in a certain tank or piece of equipment falls outside of a specified level,
What is the difference between IoT and IIoT?
Given the specific demands of industrial settings, IIoT needs to be more robust and flexible than most IoT devices. Characteristics that set them include:
What are common use cases for using a temperature sensor in predictive maintenance?
Most equipment don’t fare too well when temperatures get too high or too low, so even using a simple thermometer can be useful for detecting issues.
How do you improve operations with IoT and predictive maintenance?
The problem with PM is it’s based on the assumption that equipment failures occur on a schedule. The reality is that only 18% of assets fail based on age.
What’s the association between IoT and predictive maintenance?
Using interconnected technology allows us to network cameras and sensors easily with existing computer systems, creating automatic maintenance events.
What are some failure prediction models in predictive maintenance?
With predictive maintenance (PdM), it's understanding an asset's most probable failure modes and monitoring those conditions.
How do you apply continuous improvement to maintenance?
If you’re not focused on continuous improvement each and every day, it won’t be long before you’ll be wasting a significant amount of time and money.
What is the difference between predictive and preventive maintenance?
Although predictive maintenance is similar to preventive maintenance, this activity requires particular preset conditions.
What is level of repair analysis (LORA)?
Without getting too technical, level of repair analysis, or LORA, is a process used to determine when and where an asset should be repaired.