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What is the PAC (Programmable Automation Controller)?


PACs are programmable automation controllers. They are digital computers that hold and execute embedded programs. These are seen in many different types of electromechanical processes and usually control the machinery in factories.

This name is very similar to PLC (programmable logic controllers), which we are very accustomed to in automation. PACs are relatively new to the market and PLCs have been around since the 1960s. The arrival of these new controllers begs the question: “How are they different?”

There is no clearly defined line that differentiates the PLC and PAC. PACs are viewed as a cross between a PLC and a PC because it offers many of the advantages of both. PLCs usually use ladder logic and control discrete machinery or processes. The PAC is better suited for more complex automation solutions dealing with advanced process control, motion control, visualization, and much more. Also, the PAC uses exception based logic instead of ladder.

Advantages of the PAC 

  • Extensive analog control capabilities
  • Architecture is more open
  • PACs have lower upkeep and running cost than PC-based control
  • PACs tend to be smaller in size and more durable
  • More connectivity options
  • Runs in a scheduled cyclic mode

Having a more modular design and a more open architecture allows for the PAC to operate with HMIs, other PACs/PLCs, and different networks/systems with ease. These designs in addition to the connectivity options allow them to talk with other networks through Ethernet, fieldbus, and other forms of communication. The modular design allows for addition and removal of these communication ports. Also, this design allows for control of and data acquisition from thousands of I/O points.

PLCs vs. PACs

One of the main differences for the PLC and the PAC is the mode in which it scans. Usually, the PLC runs continuously. Once a scan completes, a new scan begins.  This works well for small applications but will begin to slow down once programs become larger. The PAC has a real-time operating system that allows it to run in a scheduled cyclic mode. It gives different programs different priorities and allows for more critical programs to run faster. This will keep the program from being slowed significantly by bulky code.

What controller is right for my process?

A lot of a PAC’s functionality is seen and available for the higher level PLCs. Does this make them PACs? It doesn’t matter what name you give your controller. The primary concern is if it meets the requirements that you need. A lot of the PLCs can be upgraded to the functionality of the PACs by buying additional hardware. The main question should be: “What is more appropriate for your industrial need?”

Price and application should be taken under consideration. The experienced technical and support staff at ACD can help!

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