| 摘要 |
<p>A method and apparatus for measurement of time required for an ultrasonic tone burst to traverse a medium from a transmitter to a receiver is disclosed. Two transducers separated by a distance through which a medium flows alternatively act as a transmitter and then a receiver of ultrasonic signals. After a signal has been emitted from the first ultrasonic transducer, the second transducer is electronically checked for receipt of the ultrasonic signal. That checking is done at certain time intervals, preferably 4 microseconds, over a selected period of time. Samples are taken over each time interval. For each sample time slot the presence and strength of an output signal is measured. An address in a memory is selected which corresponds to each sampling time slot. Each input sample is stored in memory at an address which corresponds to the time slot at which the input sample was taken. This procedure is repeated for several time intervals of the same length using subsequent ultrasonic signals from the transducer. On each subsequent transmission the input samples are combined to the input samples stored in the memory thereby producing a corresponding new process sample at each address. The process samples are periodically examined and preferably compared to a threshold level. Whenever one process sample reaches this threshold level, the time which corresponds to the time slot containing that new process sample is identified. The identified time is then taken as the time required for the signal to transverse the medium. This time can then be used to calculate various properties of the material which was traversed including the speed of sound and true gaseous flow independent of temperature, turbulence and density of the medium, distance, specific heat ratio of the medium being transversed, carbon dioxide concentration in the medium and temperature over a line path.</p> |
