Strengthen your Programmable Logic Controller


You’ve reached the ceiling of functionality with your programmable logic controller (PLC) and now want to add onboard processing, custom electronics, vision, or motion to your system without redesigning the entire thing. A programmable automation controller (PAC) can help, but you may be asking yourself, what is it, what are the advantages, and how do I get started?

What Is a Programmable Automation Controller?

A PAC combines the functionality of a PLC and a PC and is geared towards more complex automation systems.The Automation Research Corporation coined the term PAC when PLCs were reaching their limits and a new group of controllers was being created.  


4 Advantages of Adding a PAC to a PLC System 

A PAC natively supports advanced functionality like vision, high-performance analog measurements, human machine interfaces (HMI's), or FPGA technology. 


1. Improving your control application

It has been said that you can control only that which you can measure. As control applications become more and more sophisticated, you need to turn to higher-speed and higher-quality measurements. Unfortunately over the years, because of cost considerations and broad-based market needs, the PLC has become more and more tailored to general control applications with limited analog I/O and subkilohertz loop rates. Most automation engineers know the following axioms: 

  • Your outputs are only as good as your inputs. 
  • The faster you close the loop, the more precise and efficient your control. However, because of the generalized functionality of PLCs, getting high-speed, high-quality measurements, such as dynamic signal analysis, high-precision voltage, and current measurements, is often challenging without using specialized PLC hardware. CompactRIO PAC's (PACs) address these challenges by incorporating a flexible, high-performance real-time system, a highly flexible and reliable user-programmable FPGA, and high-accuracy modular C Series I/O. 


2. FPGAs a programmable chips with the reliability and performance of custom hardware

PLCs are a mainstay for industrial process control and automation applications. They are low-cost, reliable, easy to use, and have been proven with years of successful operation. Their discrete analog and digital I/O features and ability to close control loops in the hundreds-of-hertz range meet many application needs. Unfortunately, not all applications easily fit into these constraints. Many new approaches to machine building have necessitated higher performance controllers with innovative architectures. CompactRIO is a PAC that combines the real-time computing power of a computer with the reliability and flexibility of an FPGA. The FPGA portion of the heterogeneous architecture provides three core benefits over traditional control systems: high-performance parallel processing, custom hardware flexibility, and hardware logic reliability.


3.Integrating machine vision with existing systems

NI Vision products integrate easily with PLCs, PACs, and HMIs and work with a variety of cameras and imaging standards on the market, so you can choose the sensor type, resolution, and bandwidth that meets your application needs. Visit for more details.


4.Taking advantage of new technology for web and industrial connectivity

NI LabVIEW graphical programming and CompactRIO PACs optimize PLC automation and add specialty functionality, such as high-speed analog measurements, advanced analysis, and machine vision. To integrate NI PACs with existing PLCs, you can wire basic digital and analog I/O between the two systems. This method is often used because it is simple, effective, and readily available on every platform. The PAC acts as an intelligent device that carries out complex tasks and then passes the results back to the PLC’s control loop using I/O values.

Another connection method involves OLE for Process Control (OPC) technology, a standard used to access industrial devices with Windows-based software. In this manner, a PC uses the OPC client/server architecture to communicate with several different types of PLCs and PACs. This method uses industrial communications that give the controllers, sensors, and actuators the ability to communicate on the same bus without being directly wired to one another. NI offers hardware and software solutions for Modbus, PROFIBUS, EtherNet/IP, EtherCAT, FOUNDATION Fieldbus, CANopen, DeviceNet, and more, which means LabVIEW and NI PACs can easily communicate with these networks. You can integrate other specialized protocols by applying gateways as needed.


How to Get Started With Adding a PAC to Your PLC System

A PAC, like CompactRIO or an industrial PC, can be connected to an existing PLC system using analog or digital I/O or industrial communication protocols like PROFINET, Modbus TCP/IP, or OPC UA.

Analog or Digital I/O—Connect a digital or analog line from the PLC to an analog or digital module in the PAC or CompactRIO. You can use a digital or analog signal as a trigger or flag to communicate between the devices. CompactRIO, or the PAC, can do the complex tasks like vision processing and then pass the test results to the PLC to act on. 

Industrial Communication Protocols —With these industry-standard industrial communication protocols, CompactRIO can become part of the PLC system. Protocols like PROFINET, Modbus TCP/IP, and OPC UA allow for CompactRIO to be identified on the protocol network by the master PLC. To get started, you need to obtain a protocol-specific C Series module or software toolkit, which provides the interface to the protocol network. For further help understanding the different industrial communication protocols and the supported NI interface, check out Industrial Communications With CompactRIO


Presenting the NI PAC or CompactRIO Platform

The ability to communicate through industrial communication protocols, natively support the addition of vision and motion components, do high-speed processing and control, and add custom electronics with a user-programmable FPGA make CompactRIO a smart way to start preparing your PLC system for the next step. 

To learn more about CompactRIO, visit Simplify System Design With CompactRIO: The Ultimate Multipurpose Controller