Analog output from a differential travel-time current meter

Abstract

The Modular Acoustic Velocity Sensor, MAVS, measures flow components along four acoustic axes and digitizes acoustic travel-time differences that are then stored and transmitted digitally. This requires an interface to a PC or other digital data acquisition system. Analog outputs, however, free a multi-sensor data acquisition system from the timing requirements and serial input formatting requirements of an array of autonomous digital sensors. A digital to analog output circuit was added to an existing MAVS3 current meter to provide such an output for use in an array of nine MAVS3 sensors in a wave flume. While a sequence from analog to digital to analog seems awkward, it is in fact a very simple and effective means to provide asynchronous data to an existing data acquisition system. The introduction of bit noise in the conversion sequence is more than compensated for by the smoothing of the low pass filter on the analog output from the oversampled digital input. Measuring at 35 Hz with a 16 Hz low pass filter provides a signal that can be digitized without degradation and at a sampling schedule determined by the logger.