ABSTRACT

Penetrometers are instruments used in soil tillage and dynamics, site explorations, road and foundation construction and crop root growth and development research. They may have either a flat or a cone probe, depending on intended use. They may also be of the static, dynamic, proctor, pocket or digital type. A digital cone penetrometer that reads directly and displays values of soil resistance to penetration in digits via a LCD display has been designed and fabricated in this study. The instrument is made up of mechanical and electronic parts. The mechanical part consists of the handle, pressure chamber/pipe, spring, penetration shaft and a cone probe while the electronic part consists of a transmitter, transducer, receiver and display. Following the recommendations in ASAE Standards, the dimensions of the cone selected are: enclosed angle of 300, cone-base area of 323mm, and diameter of 20.27mm; mounted on a 15.88mm diameter shaft. The electronic part is made up of an infra-red displacement sensor/transducer which senses and converts changes in the displacement of the pressure shaft to digital value that indicates the measure of soil resistance to penetration or soil strength. Readings obtained on the LCD display during the field test ranged from 0.00 to 234 corresponding to pressure shaft displacements of 0.00cm to 16.00cm. The instrument was therefore found useful for measurement of soil resistance to penetration (cone index) usually required in soil strength analysis for tillage practices, agricultural machinery design and development and other related fields.