Virtualization of servers and PCs have come a long way in just a few years. It’s use in Operational Technology (OT)-based applications continues to grow.
In a Control Engineering article, Industrial virtualization heads to the plant floor, Emerson’s Vibhoosh Gupta discusses the use and application of virtualization for programmable logic controllers (PLCs), programmable automation controllers (PACs), and edge computers.
While many think of large servers hosting virtualized PC instances and thinking this approach could not work for the real-time speed requirements of PLCs and PACs, Vibhoosh explains how this is not only possible, but practical.
There are two types of virtualization, Type 1 and Type 2, depending on where the hypervisor is located. A hypervisor is the combination of hardware, firmware, and software running on the host machine and managing guest VMs.
Type 2 virtualization, which may be called “hosted,” is used for desktop and server PCs, with the hypervisor running on top of a traditional host OS already operating on the hardware. This creates virtual “sandboxes” where multiple OSs can run simultaneously, but it adds latency due to the underlying OS.
Type 1 virtualization, sometimes called “native,” utilizes a hypervisor running directly on the bare metal hardware without an underlying OS. The hypervisor partitions the hardware itself to each OS. This results in very low latency and jitter, which is ideal for real-time deterministic or time-sensitive applications. Type 1 offers greater performance than Type 2 because it has direct access to the hardware without delays due to a host OS system.
He describes how to think of PLCs and PACs as an inner loop and edge computing as an outer loop like a cascaded loop with the inner loop doing flow control and the outer loop suggesting the optimal flow rate.
Therefore, the inner loop is mission critical and must always carry on operations without fail, even if the outer loop experiences a problem. On the other hand, the outer loop is valuable, but not essential, to basic system operation.
With the PLC or PAC running real-time control on the inner loop, the outer loop running a Linux virtual machine (VM) can be:
…carefully integrated in a cooperative manner. This VM can do anything a dedicated PC could, but at a lower cost, and packaged in a more compact form factor, with no need to integrate a PC to the controller.
He highlights many applications which can provide value in this outer loop, edge VM including machine learning & analytics, communications with cloud-based apps, communications with MQTT, OPC-UA, or other, optimization calculations, and serving local display or web pages.
Read the article for more on how these real-time and edge VMs work to enable more valuable and actionable information. Also make sure to see Vibhoosh’s 4-part series on OPC-UA in the PLC, PAC Systems & Industrial Computing Forum in the Emerson Exchange 365 community.
Visit the Programmable Automation Control Systems (PLC/PAC) section on Emerson.com for more on these real-time, edge computing and other solutions to analyze and optimize your operations, to maximize productivity and minimize downtime.
