Photoacoustic Sensing System for Noninvasive and Real-Time Measurement of Paint's Viscosity in Flowing Conditions

Inline measurement of paint viscosity in the flowing conditions is extremely important for the paint manufacturing industry. This study proposes a noninvasive, cost-effective, inline method to measure paint's viscosity using frequency domain photoacoustic (PA) sensing. Through a PA signal, three different frequency and time domain features, namely, spectral amplitude ratio, acoustic attenuation, and acoustic wave velocity, are extracted. Due to the lower accuracy (<90%) of the aforementioned features, a novel statistical feature, i.e., the harmonic mean is derived from the existing features to enhance the accuracy of the measurement. To mitigate the experimental challenges, the viscosity model is trained from the PA data under static condition and tested for the paint under flowing condition. In the flowing conditions, the accuracy in the measurement is found to be less than 93%. Hence, a correction factor is introduced, which considers the Doppler shift in the PA wave velocity due to the paint flow. With this correction factor, the accuracy of the viscosity measurement is found to be greater than 95%. The developed viscosity model is validated through the fourfold cross-validation and the results are confirmed for their repeatability and tested with different paint samples.