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Session 2559

PC-Based Instrumentation System Error Calculator1

Fouad Mrad, Etienne Khayat, Kenneth Kelly American University of Beirut / National Instruments

ABSTRACT

While PC instrumentation equipment blocks catalogues are over-documented with technical specifications, it is impractical to document possible integrated system specs due to the infinite choices users have. This Instrumentation System Error Calculator estimates the total measurement error in a multistage industrial data acquisition system. The instrumentation system consists of up to four stages that lead to sense the measurand (temperature, pressure etc.) into a reading in the PC. This model-based calculator assumes independent equipment blocks in the measurement experiment setup and calculates a worst case estimate of the total error that the system would give in a real life setup. It can also be used as a model-based off-line program to help engineers and technicians select just the right equipment with acceptable tolerances for industrial tasks. The calculator prompts the user about the type of measurement and the equipment blocks of interest. Also, it asks about the environmental parameters and the operating range of the experiment. By the end of running, the calculator responds with a graph showing the total system error over the whole-required range of operation. Testing the derived model-based calculator was done in the American University of Beirut. The test was conducted with real physical equipment and the results of the experimental setup were compared to those predicted by the calculator.

I. INTRODUCTION

Signal conditioning and data acquisition are often used nowadays to read measurements from different types of transducers like thermocouples, RTDs (Resistive Temperature Devices), thermistors, and strain gauges in a PC-based setup. In many practical situations, reading a measurement into the digital computer may be inaccurate. This is the result of many factors such as the working environment and the numerous equipment blocks used in the process. Although each device in the measurement system may have its own identified and documented error values, the integration of many devices to form the whole measurement system introduces additional errors. This Instrumentation System Error Calculator calculates the error induced in the cascading of a complete measurement system components integrating the transducer, the Terminal Block eXtension module (will be called the TBX), where applicable, the Signal Conditioning eXtension for Instrumentation module (will be called the SCXI), and the Data Acquisition card (will be called the DAQ).

1 Sponsored by National Instruments as part of a “Partnership In Education” project with the American University of Beirut.

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Kelly, K., & Khayat, E., & Mrad, F. T. (2000, June), System Error Calculator In Pc Based Measurements Paper presented at 2000 Annual Conference, St. Louis, Missouri. 10.18260/1-2--8734