Simple and reliable system for gas flow regulation and measurement

Sanders, William A.; Bogan, Denis J.; Hand, Clifford W.
December 1986
Review of Scientific Instruments;Dec1986, Vol. 57 Issue 12, p3059
Academic Journal
An automatic regulation and measurement system for the delivery of gases at flow rates from about 0.01 to 1 cm³ (STP)/s is described. Flow measurement is based on the familiar direct method of determining pressure drop per unit time in a calibrated volume. The regulation and measurement functions are accomplished by simple electronic circuits. Pressure drop from the primary gas supply to the delivery point occurs in two stages. In the first stage, gas is admitted to the calibrated volume by a solenoid valve that can be opened for times as short as 10[sup -3] s. In the second stage the gas flows through a needle valve to the delivery point. The pressure in the calibrated volume is measured by a transducer. The circuit reads the transducer output and regulates the pressure by controlling the frequency and duration of the solenoid valve opening. The fluctuations in delivered gas flow are typically ±0.5%, and could be made much smaller with modest effort. This system has several advantages over commercial "mass flow meters." The relative (as opposed to absolute) error is constant. A single measurement of the "calibrated" volume suffices to calibrate the system for all gases. The gas is not exposed to heated filaments or thermistors.


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