| 摘要 |
<p>The speed of a flowing mediums is measured by determining the transit time of sound pulses transmitted alternately in opposite directions between first and second transmitterreceivers 23, 24 spaced apart in the direction of flow. A processing circuit 18, 19, 20 evaluates the speed of flow from the difference between the transit time in the two directions. The transit times in the two directions are measured by separate but identical first and second pulse circuits 11, 11'. Each pulse circuit includes a variable frequency generator 13 the frequency of which is so regulated by the transmitted pulse from the pulse generator 12 and the pulse E received from the associated transmitter-receiver that the reciprocal of its frequency is equal to the transit time in the associated direction. Delay circuitry 21 is able to delay the trigger pulse applied to the frequency generator 13 from the pulse generator 12 so as to take account of transit time errors in the apparatus.</p> |
