How to rank controllers
With the growing number of controller choices available to automation engineers, separating the chaff to find the best device for a particular application can be difficult.
Whether debating an industrial PC (IPC), programmable logic controller (PLC), or programmable automation controller (PAC), each of these devices performs essentially the same function-equipping machines with control and automation functions. However, one should always heed the "good, better, best" scale when ranking them.
Meeting the requirements
So how does one differentiate between the above choices and come to the correct decision to meet the requirements of a particular application? If designing a project from scratch, it is best to begin with this question: Will the application remain the same and never need an upgrade over the entire life of the machine? If so, then a low-cost PLC or PAC may be an option.
Realistically, most companies will need to improve, upgrade, and make changes to their applications to suit changing plant requirements not just "at some point," but repeatedly over the course of a machine's lifecycle. It is the IPC that represents the advanced, powerful, and forward-compatible choice. PC-based control platforms are the flexible alternatives for integrators who demand not just a manageable migration path, but also higher levels of power and precision from their control system. This flexibility and "upgradeability" comes from the way in which machine control is implemented with an IPC.
Functions previously handled by dedicated hardware are created in automation software as function blocks or other forms of code. These function blocks and code can be easily moved, changed, upgraded, or altered to meet the evolving needs of the enterprise. Replacing or upgrading hardware units is just as simple of a process, as the program can simply be downloaded onto the new machine controller or changed by swapping compact flash cards, bringing the machine back up after modification or service in a matter of minutes. Further expandability for machine control is assured via peripheral component interconnect express (PCIe), PCI slots, and multiple hard disk drive (HDD) slots with motherboards that are enabled with redundant array of independent disks (RAID). All of this gives controls engineers the ability to have one powerful IPC run a machine in a centralized control architecture.
Numerous computationally intensive tasks can be handled by one powerful hardware controller without overburdening the CPU by assigning specific major control functions and tasks to specific cores. In a quad-core system, for example, a machine builder can assign the PLC projects to CORE 0, motion control system to run on CORE 1, the human-machine interface (HMI) software on CORE 2, and a vision system on CORE 3. In addition, programming software efficiently distributes functions across processor cores if the user does not do so independently.
Software, as important as hardware
Enhancing this performance, flexibility, and openness, is the usual suite of standard PC- and Ethernet-based connections on all PC-based controllers, optimized for industrial use. An added benefit of these devices is that any remote access, set-up, and connection to the IPC through a secure, encrypted Internet connection require no special features, programming, or hardware. It is also a fact that the IPC brings with it a wealth of connectivity tools that is much more difficult and expensive to implement with a PLC or PAC. Using protocols such as OPC-UA, manufacturers, machine builders, and integrators can immediately create cloud-based databases and implement a robust "big data" management system-all standard with PC-based control platform. No managed hardware or dedicated "black box" equipment is required to make this happen.
These features deliver a direct positive impact on production by dramatically reducing the need for scheduled downtime as well as the frequency of unplanned downtime. Better still, PC-based controls have much more flexibility in form factor. With advanced chip designs in use, it is now possible to have a 24-core control platform, and very soon a 36-core version will represent the top end in PC-based control performance.
Hardware PLCs and PACs perform useful functions and can "get the job done," though they are narrow and difficult to change or upgrade. By moving to a PC-based platform, controls engineers gain access to all the benefits and features available from a PLC or PAC and add to this greater flexibility to cost-effectively change and upgrade functionality as plant demands necessitate.
- Reid Beilke is a product specialist at Beckhoff Automation. Edited by Eric R. Eissler, editor-in-chief, Oil & Gas Engineering, email@example.com.
- Numerous computationally intensive tasks can be handled by one powerful hardware controller without overburdening the CPU.
- PC-based controls have much more flexibility in form factor.
Will the application remain the same and never need an upgrade over the entire life of the machine?
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