HMI design comes to the industrial arena

By Heiko Luckhaupt, Category Marketing Manager, Automation & Control, RS Components




Progress in human machine interface (HMI) design has been the hallmark of developments in the consumer electronics market in the last ten years. Today, people expect all of the products that they use to look good, and to be easy to operate.

This trend is about substance as well as style. Building a smartphone HMI is obviously a complex and substantial piece of engineering. But just as much skill and expertise should go into the design of an apparently simple product such as a wireless router/modem. Here, just three or four LEDs and two push-buttons need to provide enough information for self-installation by a non-expert user, and enable remote trouble-shooting by a telephone helpdesk in the event of problems.

Many of the principles that have been learned in the consumer arena are now being applied in HMI design for industrial automation and control panels. Most striking is the increased use of graphic touchscreens to build panels that substitute for traditional “pilot” devices such as indicators, displays and switches. Many logic controller and PLC ranges also now include graphical user interfaces that have more in common with desktop PCs than with the simple buttons and meters of the past.

However, it remains true to say that modern HMI design is about more than just touch screens. By combining more traditional solutions with the new understanding of interface design, panel builders can reap the best of all worlds in terms of robustness, ease of integration, price and backward compatibility.

A distributor such as RS can offer every type of component required to make the most of this new-found flexibility – and the technical support required for panel builders to make informed, creative and reliable choices about the right solution both in building new installations and in maintaining and upgrading existing equipment.

Pushbuttons and indicators remain in the front line when it comes to monitoring and control functions: although often seen as ‘traditional’ solutions, such products have by no means been immune to technological progress.

Modern products are quick and easy to install, often without tools and with only one “pair of hands” doing the work. A range of functions, including selector switches and secure key-operated switches, are available in mounting diameters from 16mm to 30 mm. The move to LED-based illumination has increased the range of colours available to the designer, as well as cutting the energy required to produce a clear, user-friendly display. And products are now available with even greater levels of robustness and environmental sealing, for long lifetime and use under almost any conditions.

The Harmony ZB4/XB4 range from Schneider Electric exemplifies many of these trends. Designed to conform with industry standard 22mm hole fixing requirements, the Harmony ZB4/XB4 features spring return push buttons; illuminated push buttons; mushroom head emergency stop buttons with snap-action locking; LED, incandescent and neon pilot lights; selector and key selector switches.

Built to IP66 and IP69K ingress protection and complying with international EN/IEC, UL, CSA, CCC and NEMA standards, among others, these robust devices combine low-load electrical contact with high power performance. Ease and speed of installation is a key feature with a single anti-rotation locking screw that allows easy one-handed removal and mounting.

ABB also provides a comprehensive range of pilot devices, which combine with a broad portfolio of low-voltage products such as contactors, soft starts, DOL and Y/D starters, electronic relays, breakers and switches.

The company offers Modular and Compact device families: the former features a wide range of operators that can be combined with high flexibility, with a proprietary snap-on design for simple and fast assembly. The Compact Range features an all-in-one construction and rugged design for added simplicity and ease of installation.

The entire Compact Range and selected devices from the Modular Range are approved to IP67 and IP69K. This means that the products can withstand periodic submersion, as well as spray down at high pressure and temperature, as required in industries such as cement and food & beverage.

In addition to its standard and high protection range of Titan pushbuttons and indicators, Eaton offers the RMQ16 family, for applications where space is limited. The various panel elements can be mounted flush on all four sides, without any gaps. Compared with conventional 22mm ranges, using RMQ16 devices with their 18mm x 18mm front dimension, can achieve three times the information density.

The family includes two sizes of front element: 25 x 25mm and 18 x 18mm, both of which use the same standard mounting aperture of 16.2mm. Control circuit devices can be supplied with LEDs instead of filament bulbs, effectively eliminating bulb changes, because the LED service life is longer than the machine life.

For security and access control applications, Eaton also offers a fingerprint recognition module that eliminates problems caused by lost keys, misplaced ID cards or forgotten PINs. The M22-ESA requires just a standard 22.5mm diameter fitting aperture and is simple to fit using a patented Moeller tool. The system saves up to 100 different fingerprints.

The Schneider Harmony XB5R device provides an interesting variation on the push-button theme, using energy harvesting techniques to provide a wireless remote switch. The wireless connection works at a distance of up to 40m indoors, offering total flexibility of the command location and allowing the operator to move freely around the machine.

Wire-free operation not only reduces time and cost during installation, it also eliminates the risk of cable damage and of screw-terminal issues in-use. With no cable entry point, there is also less possibility of dust penetration. And energy-harvesting technology means that there is no need to replace and dispose of batteries during the life of the switch.

Finally in the push-button switch / indicator arena, Siemens’ SIRIUS 3SB3 pushbuttons and indicator lights are available both in plastic and metal, and can be easily assembled by one person using only a screwdriver.

The devices interface with control systems either via Siemens’ AS-Interface or conventional industrial controls.
For special ambient conditions such as oil resistance, the company offers both polyamide and metal versions.

Control panels often need to incorporate monitoring of quantities such as temperature, flow, pressure or speed. These not only need to be clear for the operator to read, they must also allow user interaction.

Today’s panel-mount temperature and process controllers support a range of functions, from simple on/off control to full PID. Manufacturers cater for almost any input type, including voltage, current, thermocouples and resistance devices. Devices commonly include alarm functions that can alert operators when parameters move out of tolerance.

The PA 400 process control monitor from Baumer, for example, provides a typical full feature set. Compatible with all process signals within the ranges ±10V DC or ±20mA, the device has a familiar 14mm red LED display, provides sensor fault and scale overrun alerts, and can be programmed using three keys on its front panel. In addition it provides a 24V DC / 25mA sensor output, and is available in a version with two alarm thresholds and relay output.

The need to flag alarm conditions, along with the increased robustness and flexibility of LCD display technology, has allowed increasing use of colour change techniques in alphanumeric displays, to provide operators with clearer visual messages.

Omron’s E5C-type temperature controllers, H5CX digital timers and H7CX digital counters use such a system, with a two- or three-change colour display (red, amber and green) which can be used to give a clear visual indication when set-points are reached or limits are exceeded.

Alternatively, the multi-colour capability can be used to differentiate between displays of different types of quantity – for instance counters and timers. All of these facilities are aimed at making life easier for the end user, and are designed to be easy to configure by the panel builder or installer.

While there is no doubt that traditional panel components have evolved greatly over recent years, it remains true to say that the fastest changes in the market have been driven by the incorporation of graphics-type displays.

For control of PLC-type systems, Mitsubishi offers the E Range of HMI panels that can interconnect with systems based on PLCs from Rockwell, Siemens, Omron, Eaton, Telemecanique and Mitsubishi.

These devices feature backlit LCD graphics touchscreens, and are configured using Windows programming tools. Driven by an Intel XScale RISC processor running Windows CE, they can interface with other systems via RS232, RS422/485, Ethernet or USB. A comprehensive driver library allows the status of an entire system to be monitored from a single point, enabling remote data collection and program up/download for maintenance.

Many of the major automation manufacturers also now provide support for integrating logic controller and HMI functionality into a single unit. For example, for cost-sensitive space-constrained applications, automation distributors such as RS can configure a system in which a Bosch Rexroth IndraLogic PLC system is built into a Windows CE-based touch-screen HMI system.

This approach retains IEC 61131-3 compatibility and the advantages of a PLC-type control implementation, with the familiarity and user-friendly interface of a Windows device.

Eaton has an interesting approach to this market, with its MFD-Titan system. This provides a front-panel multi-function display, compatible with standard 22.5mm mounting systems that can be coupled directly to a rear-of-panel logic controller module. By adding a clip-on digital or analogue I/O module, a complete panel-mounted controller can be built up.

A number of suppliers also provide flexible, configurable systems that aim to emulate the features of a traditional control panel via a touch screen. The PanelPilot from Lascar Electronics, for example, combines a 16-bit colour TFT display, programmable via a USB interface.

Panel Pilot allows users to choose a display type from a selection of analogue, digital and bar graph styles; the display colors colours; any text labels and scaling if required. Once all display choices have been made using a simple point-and-click application, the panel builder can save the configuration and download it to the display.

As control systems become ever more complex, the challenges for their human operators increase. Fortunately, this growth in complexity has been paralleled by a corresponding improvement in the understanding of how people interact with machines. Panel builders and control system engineers can use this new insight, along with technological progress, to produce a new generation of industrial systems that beat the complexity.