Patent ID: 8640731

Claim:
A flow rate controlling device comprising: a flow rate adjusting valve capable of adjusting a flow rate of a fuel gas, disposed in a supply duct for the fuel gas; a thermal mass flow rate sensor measuring a mass flow rate of a fuel gas, disposed in the supply duct and outputting an output that corresponds to a temperature distribution of the fuel gas, which varies depending on a heat dissipating rate of the fuel gas and a volumetric flow rate, in a vicinity of the thermal mass flow rate sensor; a first calculating portion calculating, a calorific flow rate of the fuel gas, defined as the product of the volumetric flow rate of the fuel gas and the calorific value per unit volume of the fuel gas, based on the output, is calculated from the temperature distribution of the fuel gas in the vicinity of the thermal mass flow rate sensor, from the thermal mass flow rate sensor, a proportional relationship between an inverse of the heat dissipating rate of the fluid gas and a density of the fuel gas, and a proportional relationship between the calorific value per unit volume of the fuel gas and the density of the fuel gas; and a controlling portion controlling a degree of opening of the flow rate controlling valve based on a difference between a control target value for controlling the calorific flow rate and a calorific flow rate calculated by the calculating portion, wherein the first calculating portion includes a map that is produced through calculating, in advance, a single relationship between the output of the thermal mass flow sensor and the calorific mass flow of the fuel gas, the fuel gas is a hydrocarbon combustible gas, and the single relationship applies to a plurality of compositions of the fuel gas.