Development of a TDC-based Ultrasonic Gas Flow Sensor

The transition toward modern smart gas metering is being modelled by the Measuring Instruments Directive (MID). This thesis details the development of a TDCbased (Time-to-Digital Converter) ultrasonic gas flow sensor, starting from an indepth comparative analysis of current commercial state-of-the-art solutions. Central to this work is a custom hardware architecture featuring an optimized singlepath, V-shaped conduit with a 65° incidence angle. This specific geometry is designed to match a balance: maximizing Differential Time-of-Flight (DToF) sensitivity while avoiding lateral beam deviation and signal attenuation. By operating at a transducer frequency of 500 kHz, combined with a Split Burst excitation technique and a Programmable Gain Amplifier (PGA), the system achieves picosecond-level temporal resolution and robust immunity to Cycle Slip phenomena without heavy computational loads. To further optimize metrological stability, an adaptive filter was developed for signal processing that merges the zero-flow stability of a Kalman filter with the rapid step-response of an Improved Weighted Recursive Filter (IWRF). Experimental validation on a certified test bench demonstrates that the prototype is comparable with the current commercial standards. Thanks to mechanical and hardware precision, a simple two-parameter linear calibration was sufficient to confine the percentage error between -1.04% and +1.16%, safely within the strict Maximum Permissible Error (MPE) limits required by MID Class 1.5. Finally, the optimized hardware-firmware co-design achieves an ultra-low power consumption of approximately 20µA, confirming its suitability for battery-powered smart meters.