When deciding whether to use a PLC (Programmable Logic Controller) or an IPC (Industrial Personal Computer), there is no one right answer. It would be easy to deflect an answer with a statement like ‘horses for courses’ or ‘it’s up to you’. However, each device has strengths and weaknesses, and as you gain familiarity with these, it becomes more obvious what to use when.
PLCs are specialised computers designed specifically for industrial applications. They are typically durable and are built to withstand harsh environments, high temperatures and vibration. They are designed never to stop and rarely require the ‘IT fix’ of rebooting. Being small, they are space efficient and can even be mounted on a DIN rail.
PLCs can be programmed in Function Block Diagram (FBD), Sequential Function Chart (SFC) or Structured Text (ST). The most common language used to instruct a PLC is ladder logic – where each rung of the ladder represents a logical operation, and contacts and coils represent inputs and outputs. Based on relay logic, ladder logic is easy for electricians and technicians to understand. It is ideal for real-time control and monitoring of industrial processes such as manufacturing, assembly lines, and machine control. These days, programming software is very user-friendly and easy to use. Most have a graphical user interface to drag and drop the ladder logic symbols to create the program and come with built-in debugging tools and simulators that allow the user to test the program without requiring an actual PLC.
On the other hand, Industrial PCs, known as IPCs, are more like small, regular computers that are designed to be used in industrial settings. They are typically more powerful than PLCs and can handle more complex calculations and data processing. Also, IPCs can run a wider range of software, such as Windows and Linux, as well as custom programs and applications. Some IPCs may require additional hardware or software to collect and process machine data, especially analogue data whereas PLCs natively manage this.
On the upside, IPCs can be used as HMIs (when coupled with a monitor) to display real-time data and process information for operators. In some instances, this can reduce the need for a separate hardware HMI. Furthermore, an IPC can also be used for data collection, storage, and analysis – something not easily done with a PLC.
Below is a brief outline of the benefits of each unit over the other.
Benefits of a PLC over an IPC
- Reliability: Designed specifically for industrial control systems, PLCs are built to withstand harsh environments, vibration, and temperature fluctuations. They have a longer lifespan and are more reliable than IPCs.
- Compactness: Smaller and more compact than IPCs, making them easier to install and maintain in tight spaces.
- Cost-effectiveness: PLCs are generally more cost-effective than IPCs, especially for simple control systems.
- Real-time performance: Designed for real-time control, a PLC can process inputs and outputs faster than IPCs, making them more suitable for high-speed processes.
- Industrial-grade: PLCs have industrial-grade hardware suited to a harsh environment and can withstand high temperatures, vibration, humidity and dust.
- Ease of use: PLCs are designed to be user-friendly and easy to program, even for those with limited programming experience. This makes it easier to troubleshoot and maintain the control system.
Benefits of an IPC over a PLC
- Flexibility: IPCs offer a wider range of programming options and more customisation.
- Processing power: IPCs have more powerful processors and memory than PLCs, making them better suited for running complex software and handling large amounts of data.
- Connectivity: IPCs have a broader range of connectivity options, including Ethernet, USB, and serial ports, making for easier integration with other devices and systems.
- Visualisation: with a more advanced graphical user interface (GUI) and processing power, an IPC can display data in real-time, making it easier to monitor and control processes.
- Scalability: IPCs are more scalable than PLCs because they can be expanded and upgraded as needs change.
- Support: IPCs run a broader range of software and hardware support than PLCs, thus offering a broader network to help maintain and troubleshoot
In summary, if you need a highly reliable controller for a specific industrial process and you don’t need the flexibility and power of a general-purpose computer, a PLC is probably the better choice. However, if you need a more powerful, flexible, and expandable solution, an IPC would be a better option.
The best solution is usually a combination of both devices. For example, SCADA systems are often installed on an IPC and talk to the PLC that digitises and controls real-world signals.
