A low-cost device for accurate and continuous measurements of fruit diameter

This work describes a fruit gauge based on a low-cost linear potentiometer interfaced to a data-logger, which allows continuous measurement of fruit diameter. The sensor is supported by a custom-built stainless steel frame designed to be easily applied to different size fruits. Highly significant linear relationships between tension (mV) and displacement (mm) have been found during sensor calibration. The average slope of this relationship, 5.4*10-3 with a standard deviation of 5*10-5, was used as conversion coefficient. Temperature stability was tested by submitting both the sensor and the whole gauge to a temperature range of 55 °C. The maximum deflection found was ±1mV. Measurements performed during the three developmental stages of peach (prunus persica (L), Batsch.) fruit showed high sensitivity of the gauge which allowed to clearly detect the diurnal patterns of fruit diameter changes and to precisely monitor minute variations in fruit growth rate during 24 h.