Timing arrangement for an air flow meter.
Airflow Developments Limited,
A timing arrangement for an air flow meter comprises a digital timer 60 for measuring the time interval between pairs of events, typically ultrasonic pulses transmitted and received by transducers across an air flow (figure 1) using a burst generator 52 and duplexer 54. Any set of measurements contains a plurality of time interval values, so means are provided for storing a count of the munber of occurrences of each time interval value. Each count of the number of occurrences of a particular time interval value is stored in a Random Access Memory (RAM) address 70, the address being chosen as immediately adjacent those addresses which store the counts of the number of occurrences of the immediately lower and the immediately higher time interval values. An average time interval is then derived using at least a proportion of the plurality of stored interval values. One option is to use counts of time interval values which are located within a chosen region of the time interval value found to have the greatest number of occurrences.
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