GB1212071A - Mass flowmeter - Google Patents

Abstract

1,212,071. Measuring mass flow rate electrically: venturi apparatus. TECHNOLOGY Inc. Feb. 13, 1968, No. 7078/68. Headings GIN and G1R. The mass flow rate of a fluid through a conduit is determined by a thermistor in the flow path fed with a constant current, so that its temperature is raised by the heating current and lowered by the fluid flow, the resultant temperature, as determined by its resistance, being indicative of the mass rate of flow of the fluid. The circuitry incorporates electrical means for automatic compensation for variations in ambient temperature of the fluid, and mechanical means for ensuring laminar flow of the fluid. As shown (Fig. 1), a thermistor 31, located in the flow path of a fluid through a conduit 16, is fed with a constant current from a source 22. The ambient temperature of the fluid is sensed by a second thermistor 60. The voltage across thermistor 31, as modified by the voltage across the compensating thermistor network, is measured on leads 62, 64 and is indicative of the mass flow of fluid through the conduit. The adjusting procedure to obtain full compensation for the ambient temperature of the fluid is described. To remove irregularities in the flow pattern of the fluid through the conduit, a foraminated screen is placed across the inlet, and the internal crosssectional shape is suitably tapered (Figs. 6-15, not shown). The foraminated screen may comprise a body of porous metal or foam metal to reduce any temperature difference between the fluid and the conduit. In one embodiment Fig. 14, the fluid enters conduit 180 at 182, passes over a conical shield 184 and through a series of holes 190 in the flange 188, and follows the arrows through a foraminated body 198 to outlet 183 passing temperature sensing elements 212, 214.