PLC vs. PAC: what’s the difference?

Programmable Logic Controllers (PLCs) and Programmable Automation Controllers (PACs) are industrial computers constructed and adapted for manufacturing environments. These computers are the brains of a manufacturing operation as they control automation equipment with high reliability.

PLCs and PACs are very similar to each other as they both perform the same essential functions, and with modern technology, their differences are becoming more blurred. All automated systems are built with a PLC or PAC to control each individual machine or station. Additionally, the computers can also be programmed to control a grouping of machines or stations.

So if PLCs and PACs perform the same function, what makes them different?

The most notable difference between PLCs and PACs is their programming interface. PACs are more intricate, using C or C++. PLCs on the other hand, are programmed using Ladder Logic. These programming differences create distinctions in the architecture and capability between the two computers.

PACs have an open architecture and incorporate modular design. This helps multiple devices, networks and systems communicate and operate with each other. PACs are used to communicate, monitor and control equipment across multiple networks and devices. This is possible because they utilize standard protocols and network technologies such as Ethernet, OLE for Process Control (OPC) and Structured Query Language (SQL).

By utilizing modular design, PACs simplify system expansion processes. Adding or removing components is easier to execute. PACs have the ability to monitor and control thousands of input / output (I/O) points in addition to offering tag-based programming. With tag-based programming, a single tag-name database is used for development and these tags can be assigned to a variety of functions before being tied to a specific I/O.

PLCs have simple program execution scans along with limited memory and discrete I/O. Modern PLCs are capable of high-speed I/O, sequencing and proportional-integral derivative control in addition to digital and analog I/O. Many PLCs have built in networks enabling the communication between multiple PLCs, the distribution of I/Os and communication between Human Machine Interfaces (HMI) and Supervisory Control and Data Acquisition (SCADA) systems. PLCs are particularly useful for simpler processes and smaller automation projects without the need for rapid scalability.

PACs provide more flexibility in programming, larger memory capacity and better scalability for future expansion. They are particularly useful for systems with a high percentage of analog I/O. They are often used in systems with extensive network interface requirements and in systems with direct user interaction requirements.

What does it all mean?

Based on their differences, it appears PACs are the logical choice for any automated system, but that is simply not the case. It all comes down to what is needed currently and in the future. There is no need to use a sledge hammer to simply drive a nail for hanging a photo frame. Similarly, there is no need to invest in a high-powered PAC to run machinery that requires simple programming. It all comes down to the complexities of the operation.

PLCs are ideal for both simple and high speed machine control. PLCs are a more cost-efficient option for standard automation control. Many automation projects will perform to the best of their abilities with a capable PLC. It’s the unique, large scale automation projects with intricate complexities that require a PAC. That’s why PACs are great for complex automation system architectures composed of several PC-based software applications.

PLCs and PACs both control machines in an automated process. Final determination may come down to the process’ complexities and scalability for the future. There are some instances where one is a better option than the other. Arnold Machine can recommend and program either option for your automated system.

Working with an automation expert can help find areas in your manufacturing process to save time and costs. Download our guide for helpful hints, tips and tools to find these savings throughout your operation.

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