The subject of the final project is designing a revolution speed sensor, that capable to measure revolution speed of high speed drives up to 24000RPM. Moreover, it creates a 0-10V analog voltage signal proportional to the revolution speed for feedback. The aim of the design is to achieve as small dead-time as possible, so the control loop containing the sensor can operate faster.
The revolution speed is measured with an encoder disk attached to the motor shaft and a photo-interrupter, by an ATmega328 AVR microcontroller. In the first concept the microcontroller determined the revolution speed by measuring a single period of the signal, achieving the smallest dead-time possible. After the first tests, this method was discarded, because the jitter in the signal made the measurement inaccurate. In the final solution the microcontroller measures the time required for a variable number of incoming periods. This way the measurement is accurate, and the dead-time is kept low. The measured values are sent to a computer through USB-serial interface, where a LabVIEW program displays the data, and saves into a file if necessary. Moreover it is possible to set parameters on the microcontroller from the program, for example the prescaler of the encoder wheel, or the interval of serial data transmission.
After creating the revolution speed sensor, I have made measurements in the laboratory to verify the proper operation of the device, and find the solution for possible mistakes. During the measurements development options came up, with which more accurate operation, wider field of usage can be achieved.
I have completed the task, the sensor is capable of measuring the revolution speed of high speed drives, produces an analog feedback voltage, and displays the measured data on its own display and on the computer as well.
While fulfilling the development task, I have achieved several experiences in designing mixed signal electronics, noise filtering, writing complex program for microcontroller, machine to machine communication. The gained experiences will be useful in the future as well.