Object-oriented HMI system

One of the most common classes of software packages used in automation projects is the human-machine interface or HMI. These packages provide users with the ability to monitor and supervise a control system through a configurable platform. This avoids the need for fixed control panels with dedicated control function interface devices, which present a significant expense in initial device ...

01/01/2000


One of the most common classes of software packages used in automation projects is the human-machine interface or HMI. These packages provide users with the ability to monitor and supervise a control system through a configurable platform. This avoids the need for fixed control panels with dedicated control function interface devices, which present a significant expense in initial device purchase, wiring, and maintenance.

When implementing a project where a new HMI is to be installed, users have three basic categories of systems from which to choose. These include dedicated hardware/software solutions, vendor-specific software solutions, or generic Microsoft Windows-based packages.

Lookout from National Instruments (Austin, Tex.) is a generic, Windows-based HMI system that runs in either the Windows 3.1, 98, or NT environments. It supports many common control networks and has built-in drivers for many of these communication networks. In addition, it allows multiple networks to be active at the same time, even to the point of sharing a communications port. This latter point is important if communication is required using multiple protocols over radio or other limited availability modes.

To implement graphics configuration, Lookout has a large library of standard static- and dynamic-display objects that can be selected by point-and-click. The dynamic-display objects are easy to define by pop-up windows that also aid in editing the objects. A major advantage of this system is once a control object such as a tank level is defined, it can be used in multiple contexts (numeric display, trend, bar display, etc.). Because the system revolves around control objects, database maintenance is greatly simplified.

While the package has a "Snap to Grid" function that aids in object alignment, graphic configuration would be simpler if a zoom function were available. Another problem that can arise during configuration is that Lookout does not support selection of a set of objects for group relocation; the user can only select one object or all objects.

In run mode there is no scrolling within a graphic control window. The software allows multiple panels (windows) to be opened simultaneoulsy but does not support resizing. Thus the objects in a reduced window remain full size forcing the cutoff of portions of the display. As no scroll function exists, the operator must go back to full window size to see these portions of the display. This aids in viewing alarm windows but limits the usability of the multiple window feature."

Because networking and DDE (Dynamic Data Exchange) are important to the application, Lookout supports several standard networks since it runs under Microsoft Windows. Built-in DDE support allows Lookout to share input and output values with other Windows-based packages.

This review is based upon the evaluation package for Lookout for Win32, Version 3.8 (Build 10). Current release for this package is 4.0. A full-function evaluation copy for the current release is available on the developer's web site.

For more information on Lookout, visit www.controleng.com/freeinfo .


Author Information

Contributing Editor, Tracy J. Coates P.E. is a consulting engineer at PCE Engineering, Johnson City, Tenn.




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