Programmable Logic Controller: What Is a PLC and How Does It Work?

Interconnectivity has become an increasingly critical component of the modern-day manufacturing facility. As manufacturers continue to invest in smart devices such as Industrial IoT, network-connected machinery, and similar digital tools, they must establish a way to communicate with their equipment and automate processes with minimal human intervention.

In a more traditional manufacturing setting, individual machines and control systems are connected to each other directly. However, this kind of setup can be more complex and more challenging to manage.

Modern manufacturers get around this hurdle by installing and utilizing programmable logic controllers (PLC). Instead of physically wiring each machine or piece of equipment directly to relevant control systems, manufacturers connect equipment to PLCs, making for a more integrated production process control.

In this post, we’ll discuss how programmable logic controllers are used in manufacturing facilities, what benefits they provide, and how Tulip can be used as a PLC to automate process control across machines and digital tools in your operations.

A programmable logic controller is a small computer programmed to carry out specific actions or outputs based on the inputs it receives along with a set of specific rules.

PLCs are used in a wide range of commercial and industrial settings including airports, office buildings, railways, and manufacturing facilities. In this post, we’ll review the implications of PLCs in the context of manufacturing specifically.

Connecting your equipment and systems using a PLC differs from the more traditional approach that entails using relay logic systems. While electrical relays work to control industrial processes similar to a PLC, they also pose significant drawbacks when it comes to both configurability and maintenance.

Because electrical banks are made up of a system of physical wiring, should the operation of the system ever need to be changed, the physical connections would need to be completely rewired.

Additionally, should a failure in the system take place, it would require the responsible personnel to patrol the entire system to identify the cause of the prevailing problem. Depending on the complexity of the system, this can take a significant amount of time and resources. Here’s an example of an electrical relay room for reference.

With the introduction of solid-state electronics and microchips, the command logic used by electrical relays is replaced with software logic, making PLCs significantly easier to configure and maintain.

Additionally, PLCs are built to withstand the harsher conditions often found in industrial settings making them great for manufacturing facilities.

A PLC’s job is simple to describe: run logic over and over again without missing a beat. To do that, it uses a handful of modules that each handle a specific task. Together they run in what’s called the scan cycle, a loop where the PLC reads what’s happening in the field, executes the program, updates the outputs, then starts right back at the top.

This loop doesn’t stop. On most systems it takes just a few milliseconds, which is why a PLC can react so quickly when a switch flips or a sensor changes state.

CPU and Memory
The CPU is the decision-maker. It’s where your program actually runs, and it also manages communication with the rest of the system. Inside, you’ll usually find:

• The scan cycle engine (read → execute → write)

• Storage for both the control program and the operating software

• Built-in diagnostics so you know when something’s off

• A clock for scheduling or time-based logic

Memory is split up. One part is for your program, the other is for live data things like timers, counters, and variable values that shift every scan.

Inputs and Outputs (I/O)
The I/O modules are the PLC’s link to the plant floor.

• Inputs bring in signals from sensors, limit switches, or pressure transmitters

• Outputs drive actuators, motor starters, valves, and whatever else needs a command

You’ll see two main signal types:

• Digital — simple on/off (a push button, a relay)

• Analog — variable ranges (temperature, level, speed)

Most systems are built to be expanded. If you need more I/O, you slide in another module.

Power Supply
It doesn’t get talked about much, but the power supply is critical. It converts incoming AC to the DC voltages the PLC needs. Some units include backup batteries or redundancy so you don’t lose state data during a blip in power.

Communication
Very few PLCs sit in isolation these days. They need to talk to Human Machine Interface (HMI), SCADA, other PLCs, or higher-level systems. Common industrial protocols are Ethernet/IP, Modbus, and Profinet. These aren’t just for control - they also give you diagnostics, logging, and in many plants, remote access. Some newer systems even come with wireless or cloud integration baked in.

Put it all together and you’ve got a system that’s both modular and dependable. Whether you’re running a single press or an entire production line, the underlying architecture stays the same: read the field, process the logic, update the outputs, and repeat that is fast enough to keep up with the real world.

With the proliferation of more machinery across a manufacturing facility, businesses have resorted to finding new ways to automate processes and streamline production. The increased automation led to the adoption of using programmable language controllers to connect and control the various machines, devices, sensors, etc. Some of the benefits that PLCs provide manufacturers include:

Easier programming: As discussed, relay systems require manufacturers to deal with complicated logic sequences, making the entire ordeal more challenging. PLCs, on the other hand, can be programmed in basic programming languages to control various industrial applications.

More flexibility: If manufacturers need to adjust their production processes, they can easily do so using a PLC. This is because the logic program can be easily edited via the connected computer, differing significantly from having to unwire and rewire an entire relay circuit. This allows for easier troubleshooting and maintenance over time.

Improved reliability: The fewer wiring requirements in PLC-centric automation present fewer chances for unreliable physical connections. As such, manufacturing processes can go on more reliably.

Fast response time: Modern manufacturers need instant responses to in-factory events. PLCs control machinery in real-time, enabling them to respond to inputs immediately.

For instance, if a machine’s temperature starts to shoot up, the PLC can shut down the machine almost instantaneously to prevent a more catastrophic event.

Physically robust: PLCs are built to be rugged, making them resistant to potentially extreme factory conditions like heat, dust, and debris.

When turning to programmable logic controllers for production automation, manufacturers need to consider some key factors before procuring a PLC.

These include:

• System compatibility: Manufacturers should know if their PLC of choice is compatible with their current manufacturing systems. In addition, the PLC should also be compatible with the factory’s power outlet voltage.

• Processing speed: The PLC’s CPU should possess enough processing speed to handle the various processes and functions in a given facility.

• The number of ports: It’s smart to ensure that the PLC has enough input and output ports to cover factory requirements.

• Analog I/O capability: Some PLCs can only handle simple on/off processes – discrete functions. However, some manufacturing operations have analog processes, requiring a programmable logic controller that can handle continuous variables.

• Durability: Many manufacturers position PLCs in the vicinity of the equipment of interest. Therefore, it’s important to ensure it can handle industrial environmental factors like high temperatures.

Manufacturing today isn’t as static as it used to be. Changeovers are faster, product mixes shift, and systems need to talk to each other. That’s why more teams are questioning whether traditional PLCs are always the right fit.

This is where Soft PLCs come into play. A Soft PLC does what a hardware PLC does, runs logic, controls machines but it lives in software. Instead of racks of modules, the logic runs on an industrial PC or an edge device. Because it’s software-based, updates are easier, scaling is quicker, and integration with cloud systems is built in from the start.

Tulips programmable logic controllers
With Tulip’s no-code logic builder, you can design production logic without touching ladder diagrams or Structured Text. The logic lives inside Tulip apps and can be triggered by operator actions, sensor data, or direct machine inputs. You set the rules through a drag-and-drop editor that is simple enough that engineers, supervisors, or process owners can use it without waiting on a PLC programmer. And since Tulip is designed for the shop floor, it doesn’t sit in a silo. It connects directly to machines, MES, ERP, and IoT devices out of the box.

In recent months, Tulip launched Edge IO, a wifi-enabled, easy-to-implement, low-cost edge device for collecting operational data. Our Edge IO device integrates data from various machines, sensors, and PLCs, with industrial I/O ports as well as USB connectivity.

Using Edge IO, workers can change PLC programs from Tulip apps, and our Edge IO device can be transformed into a PLC without incremental hardware cost.

You can see how Tulip is used in this context with the demonstration below :

Soft PLCs aren’t a one-size-fits-all replacement. There will always be cases where a traditional PLC is the right tool. But for many manufacturers, moving logic into software makes operations more adaptable and less tied to rigid, hardware-centric systems.

PLCs aren’t going away. They’re still the backbone of automation, and the market shows steady growth that is global Programmable Logic Controller (PLC) market was valued at $13.9 billion in 2024 and is expected to reach $22.15 billion by 2032.

What’s changing is how people use them. Plants today are more connected, and that’s pushing control systems to evolve.

A few trends stand out:

• IoT tie-ins. More sensors, more gateways, more data. PLCs are being used less like isolated boxes and more as part of a bigger connected system.

• Edge and cloud. Data and even some control logic are moving off the PLC and into edge devices or the cloud. It makes scaling easier and gives management real-time visibility across sites.

• AI creeping in. Some platforms are starting to use AI to catch anomalies, predict failures, or even optimize logic on the fly. Still early, but it’s happening.

• Soft PLCs and open setups. Teams are tired of lock-in. There’s growing interest in software-based control that’s vendor-agnostic and easier to adapt, especially in high-mix production.

The big picture: PLCs are still reliable workhorses, but the definition of “control” is shifting. It’s no longer just about keeping machines up. It’s about adaptability, data, and speed.

If you’re interested in learning how Tulip can help automate your industrial automation processes, reach out to a member of our team today!