Out of Water Vel Sensor

21st January 2020

We are investigating the Gravity Digital Microwave Sensor as a cheap alternative for a velocity sensor to a custom-designed option. The sensor uses a 10.525 GHz microwave source and uses the phase difference between the outgoing and incoming waves due to doppler shift as a measure of velocity. Unfortunately, the sensor outputs a digital high/low signal when a threshold velocity is observed, which is not useful for our application. We require a continuous analog reading to be able to accurately measure the actual velocity of water. By backtracking through the circuitry of the sensor, we managed to probe the raw measured signal which measures the amplitude of the observed velocity. The amplitude of this signal correlates with velocity. We intend to find a calibration curve which will allow us to relate the amplitude of this signal to the observed velocity.

The data taken below is a measure of the voltage output of the raw sensor data over the number of measurements. The measurement frequency is set to 5kHz. While no velocity is observed, the signal floats at around 208 which corresponds to approximately 1V. When agitated, the sensor outputs readings between 0 and 1020, (0-5V). Due to the signal floating at 208, we intend to use the time-averaged absolute difference between the current reading and 208 as a measure of velocity amplitude. As the voltage output reading is bounded, there will likely be some uncertainty in the amplitude of very high velocities, but error should be negligible when compared with noise, particularly if the sensitivity of the sensor is toggled down.