A portable firmness tester for melons was developed. It measures the t
ransmission velocity of an impulse waveform induced by an impact of a
plunger on a melon. The pistol-shaped tester has a light-touch impact
mechanism and two microphone sensors. Acoustic signals are transmitted
to a computer through a PC card-type A/D converter: The transmission
velocity calculated from the cross correlation of the two acoustic sig
nals showed a high level of correlation (R = 0.94) with apparent elast
icity measured from destructive tests. Measurements with the firmness
tester can be used to monitor physiological changes in ripening melons
.