Patent ID: 6973827

Claim:
A method of measuring a flow rate of a fluid in a fluid flow channel, comprising the steps of: obtaining a flow rate value obtained by measuring a flow rate of the fluid by indirectly-heated constant-temperature controlling flow rate measuring as a measurement with respect to a high flow rate region larger than a boundary flow rate region predetermined concerning a value of the flow rate; obtaining a flow rate value obtained by two-constant-point temperature difference detecting flow rate measuring as a measurement with respect to a low flow rate region smaller than the boundary flow rate region; obtaining a flow rate value obtained by the indirectly-heated constant-temperature controlling flow rate measuring or a flow rate value obtained by the two-constant-point temperature difference detecting flow rate measuring as a measurement with respect to the boundary flow rate region; and using a measuring section for the indirectly-heated constant-temperature controlling flow rate measuring as a heat source which heats the fluid in the fluid flow channel in the two-constant-point temperature difference detecting flow rate measuring.