Object Oriented Programming in LabVIEW for Acquisition and Control Systems at the Aerodynamics Laboratory of the National Research Council of Canada

LabVIEW has become a popular environment to develop data acquisition and control systems in aerospace simulation facilities such as those found at the aerodynamics laboratory of the National Research Council of Canada. These programs are usually developed as structured programs but with time evolve into ad hoc programs. object oriented programming (OOP) is a well established technique that has many advantages over these traditional approaches but applying OOP in LabVIEW-graphical object oriented programming (GOOP) -presents some unique challenges. However, the advantages make the effort worthwhile. The aerodynamics laboratory is undertaking a redesign and rebuild of its data acquisition and control systems in all its facilities. The new systems are required to have greater commonality, portability, flexibility, reliability, expandability and maintainability designed and built in from the start. One key to these improvements is modularity. Another is a common set of standards, policies and approach applied throughout the Laboratory. Envisioned is a system made up of subsystems with common interfaces and running common code where possible. The system should be able to be reconfigured and expanded by rearranging and adding subsystems. To some, all these requirements nicely match the properties of GOOP. A complete design in unified modeling language (UML) was done for such systems and applied to the acquisition and control system for the 0.9 m times 0.9 m pilot wind tunnel, the 5m vertical wind tunnel and to the icing spray system for the 3 m times 6 m open-circuit propulsion and icing wind tunnel to demonstrate the validity of the approach. However, the LabVIEW environment continues to evolve. LabVIEW 8.2 now incorporates GOOP as a native environment. While the new implementation offers many advantages and added functionality such as inheritance and an improved class structure, it breaks continuity with GOOP of the past thus some rethinking and redesign are required to keep up with the changes.

Introduction

In aerospace simulation facilities it is common practice to prepare a data acquisition and control software specific to the current experiment under way. This software is often a revision of a more general program that is edited for current requirements or may be a custom program written specifically for that test depending on test specifications and complexity. The softwares are written in a variety of languages such as FORTRAN, C/C++ or even custom languages and more recently environments such as LabVIEW and MATLAB. They are often written as a data flow process controlling and triggering subsystems sequentially. LabVIEW is conducive to this tradition and makes revisions easier and faster.