Deploying HMI functionality in near-edge devices for IIoT connectivity
Many manufacturers have created well-developed core-functionality for control and monitoring which is embedded in their special-purpose controllers, smart valves, meters and other near-edge devices. These intelligent devices typically connect to a programmable logic controller (PLC) or other centralized controller to pass data back and forth, and the controller often connects to a PC-based human machine interface (HMI). The HMI is the gateway to higher level computing platforms such as SCADA systems, corporate databases, ERP systems and the industrial Internet of Things (IIoT) as it possesses the required Ethernet ports, protocol support, data storage and data handling functionality.
These near-edge devices have intelligence embedded, and this is often the manufacturers’ core intellectual property. For example, a temperature controller reads temperature, executes PID loops and monitors alarm set points (Figure 1). It would typically connect to a centralized controller or an HMI via a serial port and a simple protocol such as Modbus, or via Ethernet.
Figure 1. Near-edge devices, such as this temperature controller, typically have sufficient onboard computing resources to host an embedded HMI. (Source: AutomationDirect)
Another example of a near-edge device is a power meter, which senses energy use via current and power transformers and translates this data into power information, which could then be sent to a centralized controller or HMI.
As the intelligence of near-edge devices increases, a centralized controller and HMI may not be needed for connecting to higher level computing systems and the IIoT in all cases. These near-edge devices are already handling the required real-time control and monitoring functions in their embedded platform operating system such as Linux or VxWorks.
What many of these devices don’t have is a way to get information directly to higher level computing platforms and the IIoT, bypassing the centralized controller and HMI. To implement this advanced connectivity, data collection and related functions can often be embedded directly in the near-edge device (Figure 2).
Figure 2. Adding an embedded HMI to a near-edge hardware device enables connectivity to a wide variety of other computing platforms, often via the Internet. (Source: InduSoft)
Advantages of Embedding the HMI
The advantages of this approach depend on the application. In some instances, the near-edge device could use its embedded HMI to replace the PC-based HMI for the entire machine. In other applications, the near-edge device could perform dual connectivity functions, connecting to a centralized controller to exchange real-time control information, and connecting to higher level computing platforms directly to exchange data needed for analysis but not real-time control.
In either instance, the main advantage is the built-in software drivers in the embedded HMI. Near-edge device manufacturers no longer have to create and maintain a software driver for each of the hundreds of centralized controllers, PC-based HMIs and higher level computing platforms on the market—but can simply load embedded HMI software onto their devices. Near-edge device manufacturers also don’t need to write code to create graphics for local display on their devices, as the embedded HMI can perform this function through simple configuration steps.
The result in much faster and cheaper development time for near-edge device manufacturers as custom coding is replacing by software configuration, with the compiled configuration downloaded to the device.
How to Embed HMI Functionality in Near-Edge Devices
Near-edge devices have the ability to do more than just perform their embedded control and monitoring functions. With the right software embedded, these devices can provide data collection, data storage, connectivity to higher level computing platforms, and local or remote operator interface—creating an onboard, embedded HMI. Unlike a PC-based HMI or an HMI hosted on a dedicated platform, each of which has their own integral display, operator interaction with this embedded HMI can occur in two ways:
- Through an integral display, providing the near-edge device has one
- Through the higher level computing platform(s) to which the near-edge device is connected
In most all cases, the near-edge device will retain the capability to pass data back and forth to the centralized controller. But with an embedded HMI, it can also send data directly to higher level computing platforms and the IIoT, traditionally a PC-based HMI task.
As the amount of available computing resources in near-edge devices grows due to advances in processor power and memory chips, the main issue for adding this embedded HMI capability to near-edge devices is software development. Custom coding can certainly add the required capabilities, but this is only feasible for devices with very high annual unit sales as software development, testing and maintenance costs are substantial.
Another issue with custom coding is the requirement to write drivers to communicate with the wide variety of centralized controllers and HMIs on the market, as well as the different types of higher level computing systems. A third issue is maintaining all of these software drivers through every firmware revision of the controllers, HMIs and upper-level computing systems to which they are connected. Most near-edge device manufacturers respond to this issue by only supporting a few communication protocols through their serial port and Ethernet port. This simplifies their coding and maintenance requirements, but constrains the use of their products.