Distributed Control Standard Connects Industry Regardless of Bus
May 01 2007
Page 2 of 3
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Implementing IEC 61499 In creating an automation system, one would traditionally start by looking at individual control applications and then determine how to have these interact with each other. The advent of IEC 61499 created the structure for, among other things, a supervisory application layer that connects isolated control systems. One example of this supervisory industrial networking and control software is the ISaGRAF 5 control software environment. These programming, networking, and control environments allow the designer to define the local behavior of the control devices as well as global diagrams using the IEC 61499 environment.
A library of drop-in functional blocks regulates the behaviors of the cooperating devices. Custom-made function blocks also can be dropped into the diagram to regulate the behaviors. Each 61499 function block is made of two parts (see Figure 1). The top part holds the ECC (Execution Control Chart). The IEC 61499 standard specifies that this part should be programmed using a state machine. Under ISaGRAF 5, it is programmed using an SFC (Sequential Function Chart), which happens to be an ideal state machine.
The bottom part defines the actual control function. It can be programmed using any of the IEC 61131 languages: SFC, FBD (Function Block Diagram), LD (Ladder Diagram), ST (Structured text), and IL (Instruction List). Each IEC 61499 function block is assigned to a specific resource. These resources will eventually be assigned to a given device (called configuration under IEC 61131) and one device can hold more than one resource. Therefore, an IEC 61499 diagram can span multiple resources, which may also mean spanning multiple devices. IEC 61499 helps the automation engineer to tackle a range of control challenges, from simple control challenges to very complex ones. ISaGRAF, for example, gives the engineer the opportunity to have different views over the control application and refers to these views as the Hardware view, the Resource view and the Link architecture, as illustrated in Figures 2, 3, and 4, respectively.
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