Machine builders and original equipment manufacturers needing to incorporate controls in their designs had limited options until the introduction of 'smart relays'. Jon Severn looks at recent developments in smart relays and accessories.
All but the simplest of powered equipment needs to be controlled in some way. Even lighting, which can be controlled adequately with a simple switch, can benefit from additional controls, as then the lighting can be made to stay on for defined periods, switch on and off at predetermined times, or switch on when one or more sensors are triggered. Traditionally such a control system would have been assembled using relays and timers, but 'smart relays' are a simple, low-cost alternative that offer an additional advantage in that they can be reprogrammed to modify the existing functions or to enable the smart relay to be reused on a completely different application.
In fact smart relays have more in common with programmable logic controllers (PLCs) than conventional relays, yet the term 'smart relay' is used to differentiate them and emphasise the lower price compared with even the smallest of conventional PLCs. They are programmed either by means of pushbuttons and a small screen on the front panel or, alternatively, via a computer. Smart relays were first introduced over a decade ago; very soon there were numerous different models available from suppliers of automation products, and it quickly became apparent that some were rebranded versions of others.
Today there remains a wide choice of smart relays, still with many products being rebranded versions of others. A search of the internet can help to identify which of these are identical and which have minor differences. However, given the step-change in technology that smart relays represented when they were first introduced, there seems to have been relatively little development since then.
Perhaps the most important movement in this area has come from Rockwell Automation, with the launch in February 2011 of the Allen-Bradley Micro800 family of smart relays. Featuring plug-in modules, intuitive software and exceptional versatility, these devices are said to enable engineers to specify a controller that fulfils the exact needs of their application (Fig.1).
Steve Pethick, director of components and safety business, EMEA, at Rockwell Automation, states: "Machine builders need economical, convenient control solutions they can customise to suit specific application needs. With this new line, we are delivering the functionality and flexibility of a micro PLC for the price of a smart relay. The greatest value of the new Micro800 family is the simplicity and convenience it offers users - namely, that it provides 'just enough control'; users will only pay for what they need."
An example of this approach can be seen on the front face of the Micro810, the smallest product in the family. A removable screen - which also doubles as a program storage and transfer medium - is an option as opposed to a standard feature (Fig.2). Customers can therefore opt for a lower-cost unit without a screen and program the unit via other means, or purchase multiple screenless units and one screen that can be moved from controller to controller as required for either programming or maintenance. This option, Rockwell Automation believes, is not available anywhere else at this price point.
Pethick continues: "By offering multiple plug-in modules, developed by us and our Encompass Partners - all of which are common across the line - we can help machine builders 'change the personality' of the base unit controller in order to address a multitude of different bespoke scenarios and machine sizes. Indeed, to borrow a well-worn phrase, we can now say 'there is a plug-in for that'." A clever design feature is that the plug-in modules house their own terminals, so installing additional modules does not consume valuable input/output (I/O) terminals on the base unit. Furthermore, the modules mount on the front of the base unit, not the side, so the controller footprint remains unchanged (apart from the expansion I/O modules for the Micro850, which mount on the side).
For programming the Micro800 family, Rockwell Automation has created Connected Components Workbench, a free component-class programming and configuration environment that combines all primary application development needs into a single package. Through this software and 'building block'-style application packages, customers get an estimated 80 per cent of their required infrastructure, with the remaining 20 per cent being application-specific. As might be expected today, the Connected Components Workbench follows established IEC-61131 standards, supporting ladder diagram, function block diagram and structured text programming. It also enables machine builders to configure other devices in the system, including Powerflex drives and Panelview Component human-machine interface (HMI) products. The software comes in two versions: Standard, which can be downloaded for free; and Developer, which benefits from additional functions, an offline controller simulation and advanced debugging capabilities.
As the smallest of the Micro800 family, the Micro810 programmable logic controller features embedded smart relay function blocks that can be configured via a USB port or the optional removable 1.5-inch LCD and keypad. The function blocks include Delay OFF/ON Timer, Time of Day, Time of Week and Time of Year. Outputs are rated at 8A to eliminate the need for external relays, and DC models allow four inputs to accept 0-10V analogue signals. Slightly larger versions of the Micro810 have more memory and digital I/O capability and either one or two slots for adding analogue I/O, a temperature sensor, a serial port and other plug-in modules.
For customers needing more complex functionality, the Micro830 manages up to three axes of motion. It can also accept a maximum of five plug-in modules and it benefits from enhanced communication options.
The Micro 850, the largest unit in the range, will be available at a later date and will offer embedded Ethernet/IP communications for interfacing to PCs, Panelview Component HMIs, Kinetix drives and Powerflex drives. This controller will have the same form factor as the larger models of Micro830, but will also be able to support up to four expansion I/O modules.
Of the existing smart relays on the market, one of the most sophisticated is the Zelio Logic family manufactured by Schneider Electric. These units, previously marketed under Schneider's Telemecanique brand, are available in numerous different variants, with relatively large displays and memories, which gives them a distinctive advantage in some applications. Customers also have a wide choice of accessories and add-on modules, which is one of the benefits of a product line that has evolved over a relatively long period. However, one of the shortcomings of this product line has been that the Zelio Soft programming software was not compatible with WindowsVista or Windows7. This changed in December 2010 when Zelio Soft 2 V4.4 was released, which is compatible with these newer operating systems and also WindowsXP, which is still commonly encountered in industry, even though Microsoft is withdrawing support for this superseded operating system.
As mentioned earlier, there are many suppliers of smart relays in addition to those mentioned above. In some cases the units are referred to as micro PLCs or nano PLCs, and there are also compact board-based PLCs and 'on-chip' PLCs that can be embedded within products. Over the last decade smart relays have evolved, and new add-ons and accessories have been introduced (see panel on page 22), but the Micro800 from Rockwell Automation is possibly the most exciting development. However, we will have to wait and see if this is the first of many new product launches from automation suppliers all keen to maintain their share of this very competitive market.
User interfaces for smart relays
Smart relays have created new opportunities for machine builders and OEMs, but there has also been a desire for similarly low-cost, user-friendly devices for user interaction and to enable system status to be monitored. The Logo! TD text display panel from Siemens is described as an affordable HMI that enables users to monitor the process and trace faults in the event of a problem arising (Fig.3). The display element is a backlit LCD of 128 x 64 pixels for four lines of 12 characters per line, though a text ticker feature enables a message of up to 24 characters to be scrolled across the screen. With a built-in horizontal and vertical bar graph feature, any numeric value in the Logo! Controller may be displayed, such as tank level, flow rate, speed, counts and elapsed time. In addition to the display, the IP65 Logo! TD includes six buttons for screen navigation and data entry, together with four user-configurable function buttons.
Another display has recently been introduced by Crouzet. The MTP05 touch panel, for use with the company's Millenium 3 smart relays, has a 3.5-inch screen that is said to offer excellent visibility even when using small characters; this is due to high-intensity LED backlighting that delivers superior brightness and high contrast. With its 2 MB of memory, the MTP05 can store up to 180 screens, and an intuitive symbol library is said to simplify screen creation. Directly compatible with the Millenium 3 SLin/SLout blocks, the MTP05 can control the Millenium 3 and vice versa. Fitted with an onboard battery, the touch panel offers an additional benefit in that it can securely store backup data from the Millenium 3, as well as clock data, the internal MTP05 data and the alarm history in the event of power failure. The MTP05 also archives data on an SD (secure digital) card. If required, the front panel can be protected P65