LabVIEW Graphical Programming, Fourth Edition
Written in a highly accessible and readable style, this book illustrates basic LabVIEW programming techniques as well as advanced programming concepts.
TABLE OF CONTENTS LabVIEW Graphical Programming, Fourth Edition
Sequential Control
Every process has some need for sequential control in the form of interlocking or time-ordered events. We usually include manual inputs in this area virtual switches and buttons that open valves, start motors, and the like. This is the great bastion of PLCs, but you can do an admirable job in LabVIEW without too much work. We've already discussed methods by which you read, write, and distribute data. The examples that follow fit between the input and output handlers.
Interlocking with Logic and Tables
G's boolean logic functions make ordinary interlocking simple (Figure 18.31). Boolean conditions can be derived from a variety of sources such as front panel switches, digital inputs, or comparison functions acting on analog signals. Ladder logic, as shown in Figure 18.31, is the most common language for PLC programming. It comes from the days of electromechanical switching and remains a useful documentation technique for logical systems.
Figure 18.31: Simple interlock logic, comparing a ladder logic network with its LabVIEW equivalent.
One way to add versatility to your logical operations is to use a boolean table, as shown in Figure 18.32. A table is a two-dimensional array where the columns are the mode or step number and the elements in each row represent some state of the system, such as a permissive interlock. The Mode control selects the column through the use of a 2D Index Array function. The output of the Index Array function is a ID array of booleans a column...
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