PORTABLE DEVICE (TONIMETRE) AND CARD BOARD DESIGNED FOR FAST ESTIMATION OF FRUIT FIRMNESS BY SONOMETRY

Two devices for non-destructive firmness measurement based on the acou stic impulse response method are described. They are able to digitaliz e the acoustic signal, to compute the resonance frequency with the gre atest amplitude using a Fast Fourier Transform (FFT) and to calculate the elasticity coefficient. These devices are: a) a card board for com patible computer applicable for precise and routine laboratory measure ments, and replacing a digital oscilloscope and an integrating sound m eter, b) a self-contained portable device, named ''Tonimetre'' which f acilitates measurement in situ (orchard, cold store), Measurement with the card board has a 25 ms duration and the results have the same pre cision as those of the reference method. The ''Tonimetre'' is able to digitalize the acoustic signal, to compute the resonance frequency wit h the greatest amplitude and to calculate the elasticity coefficient i n 4 s. The results obtained are adequate for fast control in orchard o r in routine analysis. The firmness determined with the Effegi penetro meter and the elasticity coefficient determined with the ''Tonimetre'' were closely related (S.D.=0.82; 975 apples). This result confirmed t hat the sonic methods are advantageous substitutes to the penetrometer test.