Abstract
Study on the accuracy of the ultrasound velocity application for chemical process monitoring is presented. Cure degree of epoxy resins was monitored in order to establish the percentage of the final cure based on ultrasound velocity of longitudinal waves. Time of flight estimations by correlation processing were used to estimate the velocity. Sources of error in the velocity measurement and their influence in the sensitivity and accuracy of the results have been studied. In order to improve the accuracy and reliability of the measurements, the use of Spread Spectrum instead of conventional excitation signals have been evaluated. Experimental results indicate that random errors of propagation time estimation are lower than velocity fluctuation over the chemical process. Spread spectrum signals provide more reliable measurements. DOI: http://dx.doi.org/10.5755/j01.eee.21.4.12783
Highlights
Composite materials are one of the most used materials in the industry nowadays, due to their mechanical properties, combining strength and lightness and because of their reduced price and ease of manufacturing
We introduce the use of spread spectrum (SS) signals instead of conventional pulse or continuous wave (CW) signals
The results indicate that time of flight estimation errors are strongly influenced by the signal energy
Summary
Composite materials are one of the most used materials in the industry nowadays, due to their mechanical properties, combining strength and lightness and because of their reduced price and ease of manufacturing. Conventional signals do not offer both parameters: pulse signals have wide bandwidth but low SNR; long continuous wave (CW) tonebursts has high SNR but narrow bandwidth and suffer from abrupt errors in peak estimation, resulting in a low temporal resolution. The aim of this investigation was to assess the reliability of the monitoring process based on ultrasound velocity measurements of the chemical curing process. For this purpose, we introduce the use of spread spectrum (SS) signals instead of conventional pulse or CW signals. We analyse the different sources of error in the velocity measurements and their influence in the accuracy of the estimates
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