Effect of data logging frequency on tracer gas measurement.

A data acquisition system which uses a computer provides a more useful analysis system. Since the processing speed of computer is continuously increasing, the information than it is possible using conventional data acquisition systems. However, the raw measurements also include the signal noise which may lead to difficulty when the signal is analyzed. This work assesses an algorithm for removing possible signal noise, usually with high-frequency, from the measurement of tracer gas concentration. The code, written by the authors, contains three main parts: fast-Fourier transformation (FFT), inverse fast-Fourier transformation (IFFT), and a digital filter. In this method, the raw data is transformed using FFT from time-domain into frequency-domain. The· digital filter, so called Notch filter, then selects the required signal without the high-frequency noise. Finally IFFT conducts inverse transformation from frequency-domain to time-domain with the frequency data selected by the filter and yields a smoothed time-domain signal back. Using this technique, the digital filtering algorithm provides the measurement data without the high frequency noise. It has been found that lHz of sampling rate is fast enough to monitor the variation of tracer gas concentration in model experiments.