Real-time measurement of Creep in fruits and vegetables using LVDT (LinearVariable Differential Transformer)

In this study, a PC based Real-Time Data Acquisition System (DAS) using Lin ear Variable Differential Transformer (LVDT) has been developed for measure ment of Creep in viscoelastic materials like fruits and vegetables. The ini tial creep occurs in a short period of time and is elastic in nature. The l ong-term deformation x(t) is smaller than initial deformation and is time d ependent. The long deformation measurement extends to many days and weeks ( K. Peleg, 1985). The present practice of measuring creep is by physical mea ns using a mechanical fixture and a measuring device and involves equipment and human error. The most sophisticated Universal testing instrument is al so being used for measurement of creep in non-linear viscoelastic solids, b ut they are quite expensive and it is under utilized and blocks the use of instrument for other tests since the creep test runs for several days. In the real time DAS, the displacement is converted into electrical output (mV) by LVDT and which in turn sends to Analog to Digital converter (PCL-20 9) via signal conditioning board. The output of LVDT (mV) is obtained into the computer via RS-232 serial port and converted to displacement using loo k up table of the calibration data of LVDT Software program is written in C language for plotting of creep and relaxation curves instantaneously. The system precludes manual recording and prevents human error. The creep data is important for developing rheological models of non-linear viscoelastic s olids.