Automação do dispositivo concha de Casagrande para o ensaio de limite de liquidez do solo

Abstract

It was developed an electronic system to automate the Casagrande-device. The whole system must be functional and practical. The motor’s angular velocity must be kept constant at two turns per second, and the completed rotation’s number must be shown to the user. And, finally, it was necessary to develop a logic to the user to operate the system. An axis with specific coupling system was developed for this project. The DC motor used is controlled by a voltage control technique called Pulse With Modulation (PWM), with the aid of an H bridge. And, to optimize the answer time of the DC motor, a PI controller has been designed. In addition, the number of rotations of the DC motor is shown on a display, and considered as number of strokes, to facilitate the register. The system has two push-button keys: one of them turn on and turn off the DC motor, in a play/pause logic (one click to turn on DC motor and another click to turn off DC motor); and, the other push-button restarts the display that show the number of rotation to the user. The microprocessing of the entire system was done through the Arduino Nano platform. The coupling of the engine next to the system proved to be practical and efficient. The DC motor axis reached the expected angular velocity, with oscillations in the answer signal obtained around the setpoint. The buttons were treated and worked correctly. The automated device was compared with a manual device, by performing the soil liquidity limit test. The data obtained by the automated system were more dispersed than the data obtained by the manual system, however the trend line of both systems is very similar.