By Steve Meyer || Programmable automation controllers (PACs) are (by design) a superset of PLCs. Everything that a PLC can do, a PAC can do. Some control tasks done by PACs are possible to do with a PLC but require expensive add-on modules. Conversely, the reliability and ruggedness so common in the physical builds of PLCs is also common in PACs. This gives PACs high operating temperatures, resistance to shock and vibration, and in some cases the elimination of rotation memory. These are typical hardware features that don’t usually incur extra cost. But taking it a step further where needed are recent improvements in the packaging domain to include explosion-proof controller ratings — which can be a great advantage in volatile environments.

Most PACs can execute IEC-61131 ladder instructions — the same as any PLC. Speed and functionality are comparable in terms of the executable I/O functions, but there are many enhancements available through PAC designs that may be beneficial in specific applications.

Programmable automation controllers and connectivity

PACs are generally sold by companies with mature I/O offerings, but the fact that PACs support Ethernet means there’s more I/O independence than ever for system designers. Design engineers can choose the I/O product that best suits a given application — or one that’s compatible with an existing installed base of products.

Integration of a PAC into data-reporting schemes is usually easy thanks to built-in communications options in the basic hardware. There’s also support for modems and wireless-network layers — for built-in remote communications to data systems outside the plant environment. There are also protocols to facilitate interfaces with data systems such as Oracle and SAP — so tools abound for using PACs in data-centric applications.

Video interfaces are more common (and growing) in discrete part manufacturing. More PACs than ever work with smart videos to verify dimensional accuracy — which in turn boosts product quality. Common video subsystems can interface directly to PACs. In the past, video-to-PLC interfaces required a great deal of extra programming.

Motion control integration into discrete part-manufacturing operations often works well on PLCs if the motion consists mostly of independent single axes. Here, a smart-axis controller built into the motor drive electronics can operate with digital handshakes to the PLC. Runs, stop inputs, and busy signals from the motor control can often suffice.

However, applications that need more coordination or speedier movements don’t run well off PLCs. That’s because PLCs limit system performance — and that can jeopardize whole automation projects.

In contrast, PACs use of high-density memory and solid state disks — so can process much more data on the fly. Should there be a machine problem, PACS can access extensive documentation or serve it under software control to facilitate repairs. That improves machine availability and productivity. In fact, these features can sometimes integrate into HMIs when there is sufficient memory. However, PACs integrate such function directly into application programming.

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