Figure 1. By combining a graphical HMI and a tough PLC into a single device, the IDEC FT2J PLC+HMI delivers space savings and installation simplicity. (Image: IDEC Corporation)

Automatically controlling equipment, and providing users with visualization of the operation, are two distinct but closely related functions. Specialized microcontrollers or commercial off-the-shelf (COTS) programmable logic controllers (PLCs) are workhorses for implementing control, while a variety of dedicated or PC-based human-machine interface (HMI) options are available.

However, implementing and integrating multiple electronic devices consumes design effort, and can be difficult when the target equipment has limited installation space. In many cases, uniting PLC control and HMI visualization roles into a single combined PLC and HMI (PLC+HMI) device can be the best approach for streamlining the effort and logistics required for complete equipment automation.

When hardwired automation first yielded to digital control, it became clear that hardening the electronic devices to survive challenging environments, and creating deterministic operating systems, would both be paramount for ensuring acceptable performance. And when physical pushbuttons and lights transitioned into far more capable graphical HMIs, developers and end users alike benefitted from the expanded potential.

Although PLCs and HMIs fulfill important and independent automation roles, they must interact closely to deliver a complete solution. Recognizing this close relationship, some manufacturers brought combined PLC+HMI devices to market, targeting applications with smaller input/output (I/O) counts and physical space constraints. However, many examples were based primarily on a PLC or an HMI, a compromise limiting designers with respect to some of the control, visualization, and performance features available with separate components.

Today, new PLC+HMI solutions are available to address these and other issues. As the size of monitored and automated manufacturing, test, and other equipment continues to shrink, designers are turning to updated PLC+HMI devices to develop comprehensive systems.

An all-in-on PLC+HMI device, especially when consolidated into a single door-mount unit, provides the best way to minimize space requirements and installation effort (Figure 1).

PLCs demand rapid real-time I/O scanning and logic solving, while HMIs need processing optimized for graphical displays. Older PLC+HMI designs sometimes attempted to use a single central processing unit (CPU) to perform these unique tasks, but modern versions provide a far better experience by using two CPUs, each optimized for its role, with both designed to natively communicate with each other.

The PLC portion can include a full instruction set, PID analog loop control, and a variety of on-board I/O, including the most common signal types, along with high-speed inputs and RTD temperature inputs. Expansion I/O modules support larger applications and I/O combinations.

Figure 2. Smartphone-like PCAP touchscreen technology, hardened for industrial use, provides the IDEC FT2J PLC+HMI with user-friendly operation and environmental resistance. (Image: IDEC Corporation)

HMI displays and older membrane and infrared touchscreens have historically been a potential weak point, exposed to environmental and user conditions that could cause improper operation, or even damage. Modern HMIs have now overcome this challenge by using projected capacitive touch panel (PCAP) technology, similar to the touchscreens on smartphones and tablets (Figure 2).

PCAP offers a glass surface resistant to false signals from dirt and water droplets. Users can use the display while wearing thin gloves, and the technology provides clear and bright images that maximize the display area while minimizing the device thickness, so space-saving shallow mounting depths are possible.

Users should confirm that any PLC+HMI solution uses a convenient single programming/configuration development environment, simplified with a drag-and-drop interface, built-in libraries, and no-cost product updates. Connectivity via Ethernet, RS232C/422/485 serial, and USB-A (supporting speakers, Wi-Fi, and Bluetooth) — along with support for popular industrial and IT communication protocols — ensures maximum usability. Trend charts, data logs, alarm logs, and other advanced objects are other key features to look for in the HMI.

Careful designers are right to question if a PLC+HMI represents a compromise. However, the most modern architectures and devices provide top performance in a space-optimized form factor, making them ideal for automating test equipment, OEM machines, and many other control and visualization applications.

This article was written by Linda Htay, Automation Product Marketing Manager, IDEC Corporation (Sunnyvale, CA). For more information, visit here .