Design of a kind of Cross-Board Type Shear StrengthMeasuring Instrument for Paddy Soil

Abstract.

.In order to obtain the shear strength of paddy soil quickly, a kind of cross-board type shear strength measuring instrument for paddy soil was designed andmanufactured, which was based on the phrase difference principle. The measuring instrument consisted of motor, transmission case, signal gear, elastic shaft, force sensor, bracket, cross-board, measuring system, etc. The measuring instrument has three different size cross-boards, 60mmx30mmx2mm, 80mmx40mmx2mm and 100mmx50mmx2mm, and it can be used to measure soil shear strength in depth from 100mm to 200mm. While using the cross-board to shear the soil, itwould bear the resistance torque which caused by sheared damage of the soil, thus the elastic shaft would be twisted for it is connected to the cross-board. The twisting angle of the elastic shaft was measuredby the signal gear fixed on it and transplated to electrical signals by a sensor. Then theelectrical signals were analyzed by an amplifier circuit fixed in the sensor and output to Single Chip Microcomputer (SCM). The SCM deal with them and converted them to shear strength and torque, which would display on the LCD screen in real-time. Based on the static calibration method, weights were hanged at the edge of the standard diameter wheel with light string to obtain standard torque values, then which were compared with measured values to calibrate the measuring instrument dynamically. The results of calibrating tests showed that the value measured by instrument had a good liner relationship between the masses of loaded weights. However, there would be initial errors. Accordingly, when measuring by the instruments, different regression equations should be taken into account, and error compensation should be taken in the program of testing system. This study provides akind of simple and rapid equipment for the paddy soil shear strength-measuring instrument.