Abstract
In this study thirteen different functions (VIs) are designed and tested .These include, single input single output, single input two outputs, latch outputs, timer, counter, logic function, less, greater and equal functions, XOR function, compound function and shift register. At the end of the study, for illustration purposes, the 7-day tea maker, electro-pneumatic drive system and their simulation were developed and tested. Results of experiment show complete coincidence between the PLC-based control and Virtual PLC-based program results.
Highlights
Today, traditional PLCs are still in use at most plants, but windows-based PCs using the LabVIEW software (Abuzalata et al, 2010; Alia et al, 2011) are increasingly becoming the preferred control mechanism for new installations
One may add that the inherent proprietary design of PLCs has limited data access for a number of reasons, such as the limited amount of memory, the nature of programming language (Relay Ladder Logic) and the data access, where data inside the PLC is stored in a data table and accessed by data table location
The second one is that if the ladder logic and the host computer program both write to a PLC register, we have an obvious conflict
Summary
Traditional PLCs are still in use at most plants, but windows-based PCs using the LabVIEW software (Abuzalata et al, 2010; Alia et al, 2011) are increasingly becoming the preferred control mechanism for new installations. An important feature of PLCs is that a standard PLC executes only a single program at a time, while an industrial computer is capable of executing several programs or tasks simultaneously in any order. Another two important PLC drawbacks may be noted : The first one is that PLC register access is performed at a surprisingly low level on most PLCs Morris (1982) and Travis and Kring (2006). Valve V1 is opened and water fills the kettle K until the float switch FS operates. Inputs: They are signals/information from sensors, which inform the PLC (LabVIEW program) what happens to the system being controlled. 7- Shift register 8- Equal comparison function 9- Less function 10- Greater or equal function 11- XOR function 12- Add function
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