JPS5710414A - Thermal type flow meter - Google Patents

Abstract

PURPOSE:To provide a thermal type flow meter which has a wide measuring range, by a method wherein a branch pipe, having branches in a plural number of stages, is mounted at a first branch pipe which branches from a main conduit, and bridge circuits, consisting of heaters, rolled around the outer circumference of each branch pipe, and resistances, are installed. CONSTITUTION:A first branch pipe 13 is mounted at a main conduit 12 equipped with a throttle mechanism 14, and a second branch pipe 15 as well as a throttle mechanism 16 is installed at the first branch pipe 13. Bridge circuits, consisting of resistance wires R3 and R4, combined with a heater, rolled around the outer circumference of the branch pipe, and resistance wires R1 and R2, are mounted at each branch pipe, and the outputs are connected to an operational unit 21 via amplifiers 19 and 20. A branch ratio of the main conduit 12 to the branch pipe 13 and of the first branch pipe 13 to the second branch pipe 15 are selected so that a quantity of flow, flowing through each branch pipe at a time of a maximum quantity of flow in the main conduit 12, covers the linear range of the bridge circuit 17. This permits the measurement of a wide range of a quantity of flow in a manner to measure the output of the bridge circuit 17 at a time of a large quantity of flow while the output of the bridge circuit 18 is measured at a time of a small quantity of flow.