Moving off the box will cause the cursor to change to what is shown in fig. 9.The first block, a summing junction, was chosen to be simple in nature to illustrate the steps in creation without unnecessary complication.
Future articles will not be as in depth with creation mechanics and spend more effort on the functionality. Modicon Concept 2.6 Series Of ArticlesThe culmination of these series of articles will be a functional turbine speed control. The programming package for this series is Modicon Concept v2.6s. This summing junction will also include two additional inputs for feedback values. These blocks will be combined to create a speed controller for a turbine. This step allows the programmer to define inputs and outputs of the function block. The function block is only accessed through the input and output pins. The inner workings of the block are hidden from the rest of the PLC program. The second input variable PrcVar represents the measured value of the quantity that we are trying to control. This function block uses the REAL data type for all inputs and outputs. There are many types available and it is possible to create compound data types made of more than one type. I will defer a discussion of these until a later article where their purpose will be made clear. This variable will represents the difference between Setpt and PrcVar speed or the system error. Click on the OK button at the bottom of the viable dialog box to close the box. Right click on the top item in the drill down named Project and the New section dialog box will appear. One could also select on of the other types of coding as well but we are programming in FDB in this article. To create a section within a group click on the group icon just left of the group name. Our function block is simple and only requires a single section. Using the icon on the tool bar, one can create a network of function blocks that resemble electronic drawings. With this blank sheet we will need to place some arithmetic predefined function blocks to process inputs and assign an output. Moving off the box will cause the cursor to change to what is shown in fig.
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