Integrated control and HMI system

Within the control system world, the definition of what platforms and tools are "typically" used in various applications is continually changing. Software applications that operate on standard PC hardware now exist in areas once reserved for dedicated hardware/software solutions. The PC is now used for more than data acquisition and operator interface functions.

04/01/2000


Within the control system world, the definition of what platforms and tools are "typically" used in various applications is continually changing. Software applications that operate on standard PC hardware now exist in areas once reserved for dedicated hardware/software solutions. The PC is now used for more than data acquisition and operator interface functions.

One major growth area is in using PCs in PLC logic control applications, where software allows the PC to emulate a PLC in terms of configuration. These "soft logic" methods can be programmed in traditional ladder logic of a PLC, but do not require the dedicated processor for execution, running instead on the PC.

Migration of the PC into more direct control applications is occurring as Microsoft Windows operating systems (95, 98, NT, and CE) become more accepted for use in control functions. Basically, the use of PCs in logic control applications is increasing, and as a result more soft logic packages are being offered.

CTC Parker Automation (Milford, O.) has released a combined software product called MachineShop that includes its MachineLogic soft logic and the Interact HMI package. This combined package allows integration of the PLC (MachineLogic) and HMI (Interact) functions under a common structure.

MachineLogic supports system configuration in any of the five IEC 61131-3 languages, including Instruction List, Structured List, Function Block Diagram, Ladder Diagram, and Sequential Function Chart. This gives users the ability to select the language that best fits their application, as well as their comfort level with these different formats.

The PLC function side of this product supports two I/O networks, Profibus and DeviceNet. These established networks give this soft logic a range of options for process interface. However, only one of these networks can be active at a time. There is no option to have them active simultaneously.

An important "extra" I/O type included in MachineShop is "Dummy I/O," which is defined as any other I/O type in the I/OConfiguration. This I/O type allows the developer to execute the program under the runtime system without being connected to a physical I/O system. This is very useful for testing and debugging purposes, as many installations do not have a development station complete with an I/O subsystem. An additional capability of this system is that the Interact HMI portion remains fully functional with the PLC in this mode.

The Interact portion of MachineShop supports more than 40 communication drivers, covering a wide range of PLC manufacturers and the different network and direct communication protocols associated with those systems. Unlike Machine-Logic, the Interact package allows more than one communication driver to be active at one time. This allows Interact to provide the interface to the MachineLogic soft logic and other traditional hardware PLCs in the same application.

Interact's graphics editor provides a good amount of flexibility, including the ability to import "dxf" type files from CAD packages. Once objects are created, linking to PLC attributes, including the details of animation, is straightforward. However, as a matter of personal preference, I do not like that the editor cannot zoom in on an area for detailed work.

In the runtime, environment Interact is easy to use and operates with PCs or a dedicated hardware platform from CTC. While this enables placement of the HMI in areas unsuitable for a PC, it brings the weakness in PC applications of requiring it to run under DOS. DOS operation prevents the user from opening other Windows applications while Interact is active. This review is based on MachineShop version 1.01 from CTI Parker Automation.

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


Author Information

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




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