OPC vs. Modbus?
OPC - Open Platform Communications
After reading about modern PLC remote control, the best solution available today is using OPC protocol. This allows the programmer to directly interact with the PLC tags and have seamless access to modern data types. LabVIEW also has made a stream lined method of pulling OPC tags into code; they act like global variables so low level VI tool kits are not needed to poll the PLC directly. I was very excited to use this protocol until I saw the price. National Instruments (NI), the developer of LabVIEW makes the user purchase the "LabVIEW Datalogging and Supervisory Control Module." This data module is coming in at $1,382, yikes! As a hobbyist this price is insane, so unfortunately this killed my dreams of using OPC.
Modbus - TCP/IP
Modbus TCP/IP is a well established protocol that communicates over local area network. Yet again LabVIEW offers a very sleek version of Modbus in the "LabVIEW Datalogging and Supervisory Control Module." However this still leaves us stuck with the hefty price tag. The good thing is NI offers a "free to download" library through of Modbus TCP/IP in VI Package Manager.
⇛ The best "free" choice will be to build a system around the Modbus TCP/IP API for LabVIEW.
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Rocket Test Stand Controller Project
This blog will cover the development of my hybrid LabVIEW & PLC rocket engine controller.