当涉及控制器时，制造商和工业公司往往倾向于留下一致的东西。毕竟，通过正确的维护，可编程逻辑控制器（PLC）可以不间断地运行，忠实地控制流程，并且在不需要更换的情况下执行其他重要功能。
But all equipment does reach the end of its lifecycle eventually. And sometimes, a company might want to add new features to enhance system control. In that case, the company will start looking at PLCs and asking system integrator partners what their upgrade path should be and whether they should add new technologies to the mix.
通常，选择很简单。如果工厂一直在使用特定的PLC家族，则迁移到工业PC上的基于软件的控制器可能很少有点。“您需要考虑支持，备件和所有权成本，”自动化工程经理Mark Brado表示JNE Consulting。“你不想卖掉它们比他们所需要更精细的东西。”
Frank Burger, senior automation specialist atAvanceon.那concurs. “Most of our customers have an installed base and it's important to them to manage their spare parts inventory. They also need to manage the training needs for their technicians who have to maintain this stuff long term,” says Burger.
由于这些原因，制造商倾向于寻找控制技术，尽管它们可能并不完美，可靠地完成工作。尽管行业依赖于验证和真实，但在需要升级之前暂停和审查控制器选项支付。
Allen-Bradley Micro820 programmable logic controllers.任何其他名称的PLC
Half a century ago, PLCs were developed as a solution to the limitations of electrical relay logic systems. They allowed engineers to develop, modify, and expand the functionality of control systems through software, rather than hardware, changes. This meant no more rooms full of wiring. Now, in the 21st century, PLCs continue to be prized for their steadfast process control reliability.
多年来，PLC制造商如Rockwell那Siemens， 和Mitsubishi Electricadded capabilities to PLC functionality, including integrated servo and drive control, network communications, advanced process control, and configurable and event-based I/O scanning. As such sophisticated functionality began appearing, the industry differentiated these advanced controllers from less complex PLCs, coining the term “programmable automation controllers” (PACs). Since the introduction of the PAC term in the 1990s, manufacturers have used it to distinguish their advanced controllers from their simpler PLCs, although the boundaries have blurred and the terms are often used interchangeably. PLCs and PACs serve the same approximate purpose, but PLCs are typically specified for basic discrete control, and PACs are used when complex features or infrastructures are required.
大多数经典PLC使用基于内存的编程形式，其中地址紧紧地耦合到物理内存结构，Nate Kay表示，高级项目工程师说Martin CSI。“Whereas with PACs, you don't have to worry about that. [PACs] are intelligent enough to let you focus on writing in the programming language, and they handle memory management in the background,” says Kay. PACs also allow tag-based programming, which increases flexibility and scalability by allowing tags to be assigned to functions before tying to specific I/O or memory addresses.
Kay说，经典的PLC仍然有他们的位置，因为它们具有成本效益，简单，并且可以多年跑步。对于从非控制背景的人来说，它们也可以更轻松地维护和排除故障。“PACS经常非常适合控制更大的过程，并集成安全，运动，分布式I / O和网络通信等事物，”他说。使用PLCS，您通常必须添加硬件模块来执行这些类型的任务。
Today when you see the term PAC, it’s usually referring to the higher-end product within a common product line, says Burger. Because the PACs and PLCs from a supplier often use the same hardware, just with different software capabilities, most people tend to call them PLCs.
Siemens Simatic S7-300 programmable logic controller.工业PCS
做车间控制在一个坚固的电脑an industrial computer is not a new concept. The Allen-Bradley SoftLogix line, which ran on the Windows 7 and Windows Server 2008 operating systems was a prominent example. Software-based PLCs feature the same programming environment and firmware as a physical PLC, says Burger. “A soft PLC is programmed and run the same way as a PLC, it's just hosted on a computer instead of on its native hardware,” he says. But PCs can run multiple applications and are generally not dedicated controllers. As a result, some suppliers have discontinued their sales of such products. For example, Allen-Bradley has sunsetted active support for SoftLogix.
另一个问题需要注意的智慧h industrial PCs (IPCs) are the updates and patches required, as with any PC. Burger says IPCs are not necessarily a technology “you expect to run trouble-free for 10 years without a power cycle. Which is exactly what you do expect from a PLC or PAC. We're replacing older PLC solutions that were installed upwards of 30 years ago, and it's still the original hardware. You don’t have that in a PC environment.”
安德鲁·阿布拉姆森，客户成功总监Grantek，有类似的角度。“在大多数情况下，我们看到工业PC随时随地从厂房移除，并将这些功能迁移到集中虚拟环境，与工厂地板上的薄客户端组合，”亚伯东说。
The virtualized environment could be either an on-premises data center or in the cloud. The drivers for these Physical-To-Virtual (P2V) migrations come from IT and include future-proofing, reducing the hardware footprint, better backup/redundancy, lower mean time to repair (MTTR), enhanced security, and a centralized management location, adds Abramson.
IPCs are most definitely used on the factory floor, but these days usually as an operator interface with a thin client. “The PLC is making all these decisions kind of in a vacuum without a human. But in reality, there is a person there and he wants to be able to start and stop the system and make, for example, vanilla instead of chocolate,” says Burger. The operators need to be able to observe what the process is doing at any given point in time. They need a window into the process be able to make changes. The role of the industrial computer then is as an HMI to provide that window into the process. Typically, you have a PLC, working in tandem with an HMI on an industrial computer to give that full functionality.
另一方面，根据Kay的说法，IPCS与控制器有一些优势。“您可以在IPC上运行数据库，协议转换器和配方管理器;您甚至可以在与自动化控制器中使用的同一工业PC上运行SCADA和MES软件。“
But this comes with the tradeoffs inherent to the PC platform mentioned above. “The Windows and Linux operating systems are not optimized for high performance in deterministic industrial applications,” Kay says.
汉堡指出，基于IPC的控制在专业的R＆D型环境中最适合，其中要求预先明确并进行大幅变化。“那里，你需要一个能够在一段时间内做出疯狂不同的事情的平台，”他说。在这种情况下，系统可能会相当快速地提供服务，[基于]完成概念验证所需的时间，例如一年左右。例如，如果您想在C ++中开发一个程序，或者，例如，您将无法在大多数PLC或PAC上做到这一点，“他补充道。
IPCs are also used in cases where there may not be an existing server or network infrastructure to support a thin client architecture. They’re also used where processing power is immediately needed, such as machine vision, adds Abramson.
The bottom line is that control systems are not one-size-fits-all. A modest traditional PLC may ably meet the requirements for a small packaging machine, whereas a PAC with advanced functionality may be required for complete packaging line control.
“每个系统都是唯一的，当指定控制解决方案时，我们始终首先考虑用户和功能要求，”亚伯东说。If you’re facing an upgrade, enlist the help of a trusted system integrator partner to weigh the costs and benefits of the different architectures including initial capital investment, ongoing maintenance costs, technical sophistication of the client, and the risks or functionality inherent to those technologies.
