| 摘要 |
In order to obtain very close control of the flowrate of a fluid through a conduit against a predetermined desired flowrate, a pulse generator is employed to produce pulses at a frequency representing the desired flowrate, and a flowmeter issues similar pulses representing the actual flowrate. First and second difference pulse streams are digitally derived to represent the difference by which the actual flowrate either exceeds or falls short of the desired flowrate, and these difference pulse streams are applied, respectively, to count down and count up inputs to an up/down counter. The instantaneous count held within the up/down counter is translated to an analog signal by a digital-to-analog converter, and the analog signal is applied to the input of a two-wire transmitter. The two-wire transmitter drives a valve-actuating motor, such as a d-c torquemotor, to correct the valve position as necessary to obtain and maintain the desired flowrate.
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