ULTRASONIC VELOCITY IN USED CORN-OIL AS A MEASURE OF OIL QUALITY

A progressive series of 10 used corn oil samples each from 3 different suppliers were created by simulated frying in the laboratory and the shear viscosity, specific gravity, and ultrasonic velocity at 2.25, 5, 10, and 50 MHz were measured at 30 degrees C. Shear viscosity increas ed from 46 mPa-s for fresh oil to 82 mPa-s for used oil. Specific grav ity increased slightly from 0.915 to 0.923 and ultrasonic velocity at 2.25 MHz increased from 1444.8 to 1451.1 m/s. The source of supply of the oil, the frequency of the transducer, and the viscosity of the oil were all found to have an effect on the ultrasonic velocity (P < 0.00 01). Ultrasonic velocity was determined to be calibrated to the oil vi scosity and thus the quality of the frying oil, however, the precision of calibration was not sufficient to detect viscosity changes reporte d to result in product defects. A technique is described using digital signals to improve the precision of time measurement in ultrasonic ve locity measurements.