Methods of assessing the time efficiency in the virtual measurement systems
Highlights
► Comparative analysis of the time measurement functions. ► Analysis of the software behavior under General Purpose Operating System and Real-Time Operating System. ► Proposal of the time analysis methodology for various systems (personal and industrial computers).
Introduction
A constant development of the computer-based measurement systems brings new challenges and problems. This imposes novel methods of system's development and analysis. Every instrument used in the professional applications is characterized according to the accuracy and speed of the data acquisition and processing [1]. In the virtual instrumentation (VI) the former depend on the data acquisition (DAQ) hardware and are usually a constant parameter (although some signal processing operations are performed to artificially increase it [2]). As the data processing operations are performed in the computer system, their speed depends on the capabilities of the hardware, operating system and the measurement application. Main categories of the computer equipment used in measurements include personal and industrial computers (for example, using PXI bus). The software part is controlled by general purpose and Real-Time operating systems (respectively, GPOS and RTOS) that run the designed measurement software. It is usually developed by the system's designer using integrated programming environments, such as LabVIEW, Lab Windows/CVI or Agilent VEE. To ensure the efficiency of the VI performing identical tasks to its traditional counterparts, a detailed time analysis must be performed. The VI relies on the internal and external clock to deliver synchronization inside the system. Depending on hardware and software configurations, multiple time measurement methods are applied, varying in accuracy and programming structures used to determine the instrument efficiency. The paper presents the study of the time measurement methods in software-based measurement systems. Their characteristics and possible applications are compared to determine conditions of the proper VI time efficiency assessment. In Section 2 problems of the measurement application execution are presented. Section 3 introduces software structures used for the time analysis of such an instrument. In Section 4 experiments using the presented functions are described. Tests for various software analysis methods on different computer platforms are included. Conclusions and hints for the designers of the VIs are in Section 5.
Section snippets
Problems of the measurement software execution
Virtual instruments present many advantages over traditional devices [3]. These include reconfigurability and wide range of the communication techniques facilitating the assembly of large-scale distributed measurement systems (DMS). Their main disadvantage is the high dependency between the software execution time, the processor speed and the operating system stability. These problems are crucial for industrial tasks (monitoring or diagnostics) [4]. Instruments designed and run under the GPOS,
Software support for the time analysis
All contemporary programming languages offer functions for the time measurement. As programs created using them are aimed mostly at GPOS, these functions have resolution of 1 ms. Integrated programming environments, such as Lab Windows/CVI or LabVIEW, are used to create industrial applications, including software for RTOS. Therefore they have two groups of functions, depending on their target of operation The main difference between them is in the accuracy and resolution. These parameters are
Experiments
The experiments related to the time measurement methods were divided into two main parts. The first one was aimed at determining the characteristics of the time measurements under GPOS, using the built-in functions Tick Count (ms) and Tick Count. The Timestamp functions are inaccessible in the traditional VI design. The second part is related to the RTOS work regime, where both simpler and more sophisticated functions of the time measurement were compared.
To perform the examinations, LabVIEW
Conclusions
The conducted experiments show the following characteristics of the time measurement mechanisms present in the modern integrated programming environment:
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Due to limitations of GPOS, attempts to measure duration of operations with the resolution greater than 1 ms are not reliable and should not be used in the software development process.
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Efficient software development requires considering the “worst case” scenarios [12] and assuming the longest possible durations of the analyzed functions. They
Prof. Wieslaw Winiecki is with the Faculty of Electronics and Information Technology, Warsaw University of Technology. He is the Head of the Computer-Aided Measurement Laboratory in the Institute of Radioelectronics. He is the author or co-author of 4 books and 170 papers. His research areas include: measurement systems, virtual instruments, modern communication and software technologies in distributed measurement and control systems. Prof. Winiecki is a member of the Metrology and
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Prof. Wieslaw Winiecki is with the Faculty of Electronics and Information Technology, Warsaw University of Technology. He is the Head of the Computer-Aided Measurement Laboratory in the Institute of Radioelectronics. He is the author or co-author of 4 books and 170 papers. His research areas include: measurement systems, virtual instruments, modern communication and software technologies in distributed measurement and control systems. Prof. Winiecki is a member of the Metrology and Instrumentation Committee, Polish Academy of Sciences; and is the President of the Polish Society for Measurement, Automatic Control and Robotics (POLSPAR), and a member of IEEE.
Piotr Bilski, PhD, was born in 1977 in olsztyn, Poland. He graduated from Warsaw University of Technology, Institute of Radioelectronics, obtaining his MSc degree in 2001 (with honors) and PhD degree in 2006 (with honors). Currently he is an Assistant Professor in the Institute of Radioelectronics, Warsaw University of Technology and Department of Applied Informatics, Warsaw University of Life Sciences. He also holds the position of Vice-Dean in Charge of Students there. His main scientific interests are diagnostics of analog systems, design and analysis of virtual instrumentation, application of artificial intelligence and machine learning methods to the environmental sciences.