HIGH-SENSITIVITY GAS MICRO-FLOWMETER Russian patent published in 2016 - IPC G01F1/68 

FIELD: measuring equipment.

SUBSTANCE: invention relates to measurement equipment, namely to thermal micro-flowmeters for measuring gas flow rate within the range of (0÷5) mg/sec. Micro-flowmeter operates in the mode of alternating internal heat release power. In the proposed two-channel micro-flowmeter a measuring thermistor and a constant resistor are elements of the circuit of a resistive voltage divider. At constant voltage of the supply circuit U₀ = const when in consumption the thermistor resistance grows, that leads to reduced current in the circuit and, as the result, to redistribution of voltage drop on elements of the circuit: thermistor voltage U_tr(G/2) grows, and on the resistor U_R(G/2) falls so, that their sum is equal to the supply voltage: U_tr(G/2)+U_R(G/2)=U₀. Placing at the outlet channels of identical diaphragms with holes of a set value (diameters 1; 1.5; 3 mm) reduced available for measurement range of the gas flow and thereby lead to a significant increase in sensitivity by the flow rate - maximum one of 36.4 and 28.8 V/(mg·sec^-1) in N₂ and Ar respectively; medium-range one ~19 V/(mg·sec^-1) and the accuracy of measuring the gas flow rate. Herewith temperature independence of the micro-flowmeter is saved. Method of measuring gas flow rate consists in placing thermistors in gas flows with flow rate G/2. Introduction as a control one the thermo-stabilizing thermistor in the heat carrier thermal mode stabilization circuit at specified temperature levels T_u provides temperature independence of the flow meter irrespective of the gas flow rate. Output signal is generated as the difference of voltages drop on the measuring thermistor and the resistor: U(G)=U_tr(G/2)-U_R(G/2). Recorded voltages on elements of the circuit vary within the range of (25÷85) V. In absence of the flow rate voltages on the elements are equal and make half the supply voltage: U_tr(0)=U_R(0)=U₀/2. Flow meter comprises: housing 1; heat exchanger housing 2; gas distribution chamber 3; channel 4 with measuring thermistor 5; channel 6 with thermo-stabilizing thermistor 7; heating spiral 8 of the heat exchanger; additional spirals 9 and 10 on surfaces of the channels; power control unit 11 (PCU) of heat exchanger spiral 8 and of additional spirals 9, 10; R(T_o) - resistance of the resistor. In its values the proposed micro-flowmeter does not have any domestic and foreign analogues.

EFFECT: reduction of available measurement range of gas consumption, higher sensitivity by the flow rate and accuracy of measuring the gas flow rate.

1 cl, 1 dwg