Patent ID: 6272919
Filing Date: 2001-08-14
Classification: G01F

Abstract:
Method for determining a flow rate value of gas inside a channel in which there is arranged a first sensor which is connected to processing means for driving the first sensor, comprising:alternately driving the first sensor to heat it and to let it cool down;measuring a current cooling rate value (Mx) of the first sensor during its cooling down;during a calibration stage, supplying the gas or a different gas at different flow rates to the channel, measuring for each of said flow rates of the gas or the different gas a pair of flow rate value (.phi.j) and a cooling rate value (Mj) of the first sensor and preparing a calibration table containing such pairs of values (.phi.j, Mj);after calibration applying the calibration table in determining a current flow rate value (.phi.y) dependent on the current cooling rate value (Mx) of the first sensor and on the calibration table;deriving an auxiliary flow of the gas from the channel towards a chamber, the auxiliary flow being a magnitude of basically zero with respect to a main flow inside the channel to keep the gas inside the chamber basically at stand still, while a second sensor of the same type as the first sensor being arranged inside the chamber and connected to and to be driven by the processing means;alternatively driven the second sensor to heat it and to let it cool down;measuring a cooling rate value (Zx) of the second sensor during its cooling down;compensating the current cooling rate value (Mx) of the first sensor to provide a compensated cooling rate value (My) on the basis of cooling rate values (Ma, Za) of both sensors obtained recently for the gas prior to the measuring of the current cooling rate value (Mx) and cooling rate values (Mg, Zg) of both sensors obtained previously at stand still of the gas inside the channel and the chamber, and in which the flow rate value (.phi.y) of the gas inside the channel is determined from the compensated cooling rate value (My) by means of the calibration table.