CHIRP EXCITATION OF ULTRASONIC PROBES AND ALGORITHM FOR FILTERING TRANSIT TIMES IN HIGH-RANGEABILITY GAS-FLOW METERING

The signal processing used in an ultrasonic high-rangeability gas flow meter using times-of-light, is presented. The How meter under discussion, uses a combination of continuous wave and chirp signals to measure at low flow velocities, below 20 m/s, and chirp signals alone, to measure high flow velocities, above 20 m/s. Because of the necessity of pulse compression technique in the signal waveform design, a discussion on the technique of pulse compression and choice of signal waveforms is given. Hereby, the advantages and disadvantages of amplitude weighing vis-a-vis frequency domain manipulations of the waveforms are also discussed. The adaptive signal processing based on pulse compression is the most important feature in achieving high-rangeability ultrasonic gas How metering. The paper aims at an insight building and practical presentation of pulse compression. Via matched filtering, some fundamental properties of pulse compression are discussed. To eliminate spurious times-of-flight, the usage of special filtering technique is presented, based on assessing the gradient of ascendingly ordered time series of times-of-flight measurements. A summary of user experience of high-rangeability gas flow meters in use on different offshore platforms and in refineries, is given. Long term tests that looked into the accuracy of the high-rangeability flow meter are also described.