Patent ID: 6983214

Claim:
A method of measuring a flow rate of fluid by: moving the fluid within a fluid flow path, measuring an electrical output corresponding to the flow rate of the fluid within the flow path by utilizing an electrical circuit having a thermal type flow sensor disposed in the fluid flow path and by measuring heat absorption of the fluid with the thermal type flow sensor, measuring a temperature of the fluid, converting a value of the electrical output to a value of the flow-rate by utilizing a plurality of predetermined calibration curves T 1 to T k (k is an integer greater than 1): indicating a relationship between the electrical output of the electrical circuit and the flow rate of the fluid at a plurality of discrete temperature values t 1 to t k respectively, each of the calibration curves having discrete flow rate values in response to discrete electrical output values E AR1 to E ARj (j is an integer greater than 1), and achieving a corrected flow rate value F t corresponding to the temperature at the time of measurement on the basis of a value of the measured temperature and the calibration curves by interpolation calculation, wherein the interpolation calculation is carried out on the basis of a value of the measured electrical output and a measured temperature value t by using the calibration curves T n , T n+1 (n is an integer smaller than k−1) satisfying t n ≦t <t n+1 to achieve flow rate values F ab , F AB , which correspond to the measured electrical output value E h by using the following equations (1), (2): F ab =( F a −F b )·( E h −E ARm )/( E ARm+1 −E ARm ) +F b (1) F AB =( F A −F B )·( E h −E ARm )/( E ARm+1 −E ARm ) +F B (2) wherein m is an integer smaller than j−1, electrical output values E ARm ,E ARm+1 satisfy E ARm ≦E h ≦E ARm+1 , and F b , F a are flow rate values on the calibration curve T n for the electrical output values E ARm , E ARm+1 respectively, and F B , F A are flow rate values on the calibration curve T n+1 for the electrical output values E ARm , E ARm+1 respectively, and to achieve the corrected flow rate value F t corresponding to the measured electrical output value E h for the measured temperature value t by using the following equation (3): F t=( F ab −F AB )·( t−t n+1 )/( t n −t n+1 ) +F AB (3).